Ch.6 - Thermochemistry See all chapters
All Chapters
Ch.1 - Intro to General Chemistry
Ch.2 - Atoms & Elements
Ch.3 - Chemical Reactions
BONUS: Lab Techniques and Procedures
BONUS: Mathematical Operations and Functions
Ch.4 - Chemical Quantities & Aqueous Reactions
Ch.5 - Gases
Ch.6 - Thermochemistry
Ch.7 - Quantum Mechanics
Ch.8 - Periodic Properties of the Elements
Ch.9 - Bonding & Molecular Structure
Ch.10 - Molecular Shapes & Valence Bond Theory
Ch.11 - Liquids, Solids & Intermolecular Forces
Ch.12 - Solutions
Ch.13 - Chemical Kinetics
Ch.14 - Chemical Equilibrium
Ch.15 - Acid and Base Equilibrium
Ch.16 - Aqueous Equilibrium
Ch. 17 - Chemical Thermodynamics
Ch.18 - Electrochemistry
Ch.19 - Nuclear Chemistry
Ch.20 - Organic Chemistry
Ch.22 - Chemistry of the Nonmetals
Ch.23 - Transition Metals and Coordination Compounds

Enthalpy of Formation

See all sections
Sections
Internal Energy
Calorimetry
Hess's Law
Enthalpy of Formation
End of Chapter 6 Problems
Additional Practice
Units of Energy
Endothermic & Exothermic Reactions
Additional Guides
Enthalpy

In a formation equation one mole of product is formed from the standard or elemental forms of each element. 

Formation Equation

Concept #1: Understanding a Formation Equation

Concept #2: Understanding Heats of Formation

Enthalpy of a Reaction

The enthalpy value associated with an element or compound can be used to find the enthalpy of a reaction. 

Example #1: The oxidation of ammonia is given by the following reaction:

4 NH3 (g) +  5 O2 (g) →  4 NO (g)  + 6 H2O (g)

Calculate the Horxn if the Hof value for NH3 , NO and H2O are -45.9 kJ/mol, 90.3 kJ/mol and -241.8 kJ/mol respectively.

The enthalpy of a reaction can be determined if we are given the enthalpy of formation value for each compound. 

Practice: Ibuprofen is used as an anti-inflammatory agent used to deal with pain and bring down fevers. If it has a molecular formula of C13H18O2 determine the balanced chemical equation that would give you directly the enthalpy of formation for ibuprofen.


Example #2: Use the following bond strength values (kJ/mol):

C–H  412          C–O  360          C=O  743           

C–C  348          H–H  436          C=C  611

C≡C  837         C≡O  1072        O–H  464

O=O 498

Calculate the enthalpy of the reaction shown in the formula below: 

When given bond energies then calculating the enthalpy of the reaction requires a different equation. 

Additional Problems
Use the information provided to determine ΔH°rxn for the following reaction: CH4(g) + 3 Cl2(g) → CHCl3(l) + 3 HCl(g             ΔH°f (kJ/mol) CH4(g)        -75 CHCl3(l)    -134 HCl(g)         -92 A) -151 kJ B) -335 kJ C) +662 kJ D) +117 kJ E) -217 kJ
Choose the thermochemical equation that illustrates ΔH°f for Li 2SO4. A) 2 Li+(aq) + SO42- (aq) → Li2SO4(aq) B) 2 Li(s) + 1/8 S8(s, rhombic) + 2 O2(g) → Li2SO4(s) C) Li2SO4(aq) → 2 Li +(aq) + SO42-(aq) D) 8 Li2SO4(s) → 16 Li(s) + S 8(s, rhombic) + 16 O2(g) E) 16 Li(s) + S8(s, rhombic) + 16 O2(g) → 8 Li2SO4(s)
Given the data in the table below, what is ΔH°rxn ? 4NH3(g) + 5O2(g) → 4NO(g) + 6H2O(l) A) -1172 kJ B) -150 kJ C) - 1540 kJ D) -1892 kJ
Determine the answer for the question below.
Which of O2 (g), O2 (ℓ), H2 (g), H2 (ℓ), H2O (g), H2O (ℓ) have a heat of formation equal to zero? 1. O2(g), O2(ℓ), H2(g), H2(ℓ) 2. O2(g), H2(g) 3. O2(g), O2(ℓ), H2(g), H2(ℓ), H2O(g), H2O(ℓ) 4. All of them, but only at absolute zero 5. O2(g), H2(g), H2O(g)
Predict the value of ΔHo f is greater than, less than or equal to zero for the following elements at 25oC. a) Cl2 (s)                                                                        b) Hg (g) 
Predict the value of ΔHo f is greater than, less than or equal to zero for the following elements at 25oC. a) Pb (g)     b) S8 (s, rhombic)
2C2H2  +  5 O2  →  4CO2  +  2H2O  Use the given standard enthalpies of formation to calculate ∆H for this reaction C2H­2 = 227.4 CO2 = -393.5 H2O = -241.8 1256.2 kJ      b. -1256.2 kJ       c. -2512.4 kJ        d. 2512.4 kJ
If the combustion of liquid octane, C 8H18, has a heat of reaction that is equal to –10.94 kJ, calculate the standard heat of formation of CO2. 
Which of the following equations represents a reaction that provides the enthalpy of formation of NaClO3? A. NaClO(s) + O2(g) → NaClO3(s) B. NaClO2(s) + 1/2 O2(g) → NaClO3(s) C. NaClO2(s) + O(g) → NaClO3(s) D. Na(s) + Cl(g) + 3/2 O2(g) → NaClO3(s) E. Na(s) + 1/2 Cl2(g) + 3/2 O2(g) → NaClO3(s)
Urea, CO(NH2)2(s), is an important molecule. Our bodies convert the nitrogen from metabolizing proteins in urea which is less toxic than ammonia and can be stored in the kidneys until released. (Fish, on the other hand, release ammonia directly into water through their gills.) Urea was the first “biological” compound to be synthesized entirely from inorganic compounds. Before then, biological processes were thought to require a “vital force” that only existed in living systems.  Industrial synthesis of urea generally follows the Bosch–Meiser process. A balanced chemical equation for the overall reaction is given below. 2NH3(l) + CO2(g) → (NH2)2CO(s) + H2O(l)  Determine ΔH°rxn for the above reaction.          Is this reaction endothermic or exothermic?
For which one of the following reactions is ΔH°rxn equal to the heat of formation of the product? A) 12C (g) + 11H2 (g) + 11O (g) → C6H22O11 (g) B) N2 (g) + 3H2 (g) → 2NH3 (g) C) P (g) + 4H (g) + Br (g) → PH4Br (l) D) 1/2 N2 (g) + O2 (g) → NO2 (g) E) 6C (s) + 6H (g) → C6H6 (l)    
Use the standard enthalpies of formation in the table to calculate Δ H° for this reaction. 2 CrO42- (aq) + 2 H+ (aq) → Cr2O72- (aq) + H2O (l) a) +272.1 kJ b) +13.7 kJ c) -13.7 kJ d) -272.1 kJ
What is the value of ΔH° for this reaction? 3 H2 (g) + O3 (g) → 3 H2O (l) a) -15 kJ b) -558 kJ c) -722 kJ d) -994 kJ
Calculate the enthalpy of combustion of ethylene, C 2H4, at 25°C and one atmosphere pressure. C2H4(g) + 3 O2(g) → 2 CO2(g) + 2 H2O(l) a) -1411 kJ b) 1254 kJ c) -732 kJ d) -627 kJ
Use the given heats of formation to calculate the enthalpy change for this reaction. B2O3 (s) + 3 COCl2 (g) → 2 BCl3 (g) + 3 CO2 (g) a) 694.3 kJ b) 354.9 kJ c) -58.9 kJ d) -3917.3 kJ
Using the given thermochemical data, what is ΔH° for this reaction? 2 CH3OH (l) + O2 (g) → HC2H3O2 (l) + 2 H2O (l) a) 583 kJ b) 535 kJ c) -583 kJ d) -535 kJ
What is the enthalpy change for this reaction? Hg (l) + 2 Ag+ (aq) → Hg2+ (aq) + 2 Ag (s) a) +65.5 kJ b) +40.1 kJ c) -40.1 kJ d) -65.5 kJ
When 10.00 g of phosphorus is burned in O2(g) to form P4O10(s), enough heat is generated to raise the temperature of 2950 g of water from 18.0 °C to 38.0 °C. Calculate the enthalpy of formation of P4O10(s) under these conditions. 
The value of ΔH° for the following reaction is -3351 kJ: 2Al (s) + 3O2 (g) → 2Al2O3 (s) The value of ΔHf° for Al2O3 (s) is __________ kJ.   a) -3351 b) -1676 c) +3351 d) -16.43 e) -32.86
Calculate ΔH°rxn for the following reaction and indicate whether it is exothermic or endothermic. 2H2 O2 (l) →2H2 O(l) + O2 (g) Given that ΔH°f[H2 O(l)] = -285.8 kJ/mol and ΔH°f[H2 O2 (l)] = -187.6 kJ/mol. ______________________________
The value of ∆H0 for which of the following reactions is referred to as the standard molar enthalpy of formation of carbon monoxide? 1. C(g) + 12 O2(g) → CO(g) 2. C(graphite) + 1/2 O2(g) → CO(g)  3. C(graphite) + O(g) → CO(g) 4. C(g) + O(g) → CO(g)
Find the standard heat of formation (ΔH f) for butanol, C4H10O(l) given the following combustion reaction and information below: 2C4H10O (l) + 12O2 (g) → 8CO2 (g) + 10H2O (l)     ΔH = -2676 kJ H2O (l)  ΔH f = -285.8 kJ/mol CO2 (g) ΔHf = -393.5 kJ/mol a. + 832.5 kJ b. - 998.4 kJ c. - 1665 kJ d. - 1483 kJ e. - 378.9 kJ  
What is the standard enthalpy of reaction ΔH orxn for the following reaction using the standard enthalpies of formation provided ? SiCl4(l) + 2H2(g) + O2(g) → SiO2 (s) + 4HCl(g)              ΔHorxn = ? ΔH°f(SiCl4) = -640.1 kJ/mol   ΔH°f(HCl) = -92.3 kJ/mol ΔH°f(SiO2) = -910.9 kJ/mol
Determine the enthalpy of reaction for 4 NH3(g) + 7 O2(g) → 4 NO2(g) + 6 H2O(l) 1. −1397.6 kJ/mol rxn  2. +2034.4 kJ/mol rxn 3. −1899 kJ/mol rxn 4. −298.7 kJ/mol rxn 5. −1766 kJ/mol rxn
In the standard enthalpy of formation, ΔH°f , for nitrogen(IV) oxide, NO2, is the enthalpy change for which reaction?  (A) N(g) + 2O(g) → NO2(g) (B) 1/2N2(g) + O2(g) → NO2(g) (C) 1/2N2O4(g) → NO2(g) (D) NO(g) + 1/2O2(g) → NO2(g)
Given the following:
Which of the following has a non-zero ΔHf°?   a. O2 (l) b. C (graphite) c. N2 (g) d. F2 (g) e. Cl2 (g)
The explosive nitroglycerin (C3H5N3O9) decomposes rapidly upon ignition or sudden impact according to the following balanced equation: 4C3H5N3O9(l) → 12CO2(g) + 10H2O(g) + 6N2(g) + O2(g)    ΔH∘rxn =  −5678 kJ Calculate the standard enthalpy of formation (ΔH∘f) for nitroglycerin. A) −365.5 kJ B) −1462 kJ C) 1462 kJ D) −5678 kJ E) −5408.2 kJ
The combustion of ammonia is represented by this equation: 4NH3(g) + 5O2(g) → 4NO(g) + 6H2O(g)       ΔH°rxn = -904.8 kJ What is the enthalpy of formation of NH 3(g)?
Consider 0.0110 moles of HCl consumed in the chemical reaction at standard temperature and pressure: 2 HCl (aq) + Mg (s) → MgCl2 (aq) + H2 (g) ΔHf° (HCl) = −167.2 kJ;  ΔH f° (MgCl2) = −801.2 kJ   Identify the statements below as either true or false.   Magnesium is undergoing oxidation. Mg has the most protons of any atom in the reaction. The reaction will form 0.123 L of H 2 gas. The reaction will also consume 0.134 g of Mg. The ΔH of the reaction cannot be calculated. The energy change from the reaction, q rxn = −2.57 kJ.
Calculate ΔH for the following reaction using the given enthalpies of formation. 2NO(g) + 5O2(g) → 2NO2(g) ΔHfNO(g) = 90.25 kJ mol-1 ΔHfNO2(g) = 33.18 kj mol-1 a. +57.07 kJ b. -57.07 kJ c. +114.14 kJ d. -114.14 kJ e. +66.36 kJ
Calculate ΔH for the reaction C4H4(g) + 2H2(g) → C4H8(g), using the following information: ΔHcombustion for C4H4(g)= -2341 kJ/mol ΔHcombustion for C4H8(g)= -3071 kJ/mol ΔHcombustion for H2(g) = -286 kJ/mol a. -128 kJ b. -316 kJ c. -158 kJ d. -700 kJ e. -4810 kJ
Consider the following reactions: 1.   2Al(s) + 3/2 O2 (g) → Al2O3 (s)        ΔH° = -1669.8 kJ/mol   2.   H2 (g) + 1/2 O2 (g) →  H2O (l)         ΔH° =    -285.8 kJ/mol 3.   H2O (s) → H2O (l)                           ΔH° =       6.01 kJ/mol For which, if any, reactions does ΔH° correspond to a molar enthalpy of formation?    Write the oxidation numbers in the spaces provided.    
ΔHf° is not zero for which one of the following: O­2(g) C (graphite) F2(s) H2(g) Br­2(l)  
The combustion of ammonia is represented by the equation. 4NH3(g) + 5O2(g) → 4NO(g) + 6H2O(g)      ΔH=-904.8 kJ What is the enthalpy of formation of NH 3(g)?   Enthalpy of Formation Data NO(g)         +90.4 kJ/mol H2O(g)        -241.8 kJ/mol A) -449 kJ/mol         B) -46.1 kJ/mol           C) -184 kJ/mol       D) 227 kJ/mol
Find the ΔH of for propanol, C3H8O(l), given the following information: C3H8O (I) + 9/2 O 2 (g) → 3 CO2 (g) + 4 H2O (g)     ΔH ocomb = 2021 kJ ΔHof of CO2 (g) = - 393.5 kJ/mol ; ΔH of of H2O (g) = - 241.8 kJ/mol A. -1642.5 kJ B. -2021 kJ C. -4168.7 kJ D. -2656.3 kJ E. -126.7 kJ    
The thermite reaction, in which powdered aluminum reacts with iron oxide, is highly exothermic. Use the standard enthalpies of formation given to find the ∆H°rxn for the thermite reaction.                    2 Al   +   Fe2O3   →   Al2O3   +   2 Fe ∆H Fe2O3 = -824.2 kJ/mol ∆H Al2O3 = -1675.7 kJ/mol
For which of the following reaction(s) is the enthalpy change for the reaction equal to ∆Hf° of the product? I. 2 F (g) → F2 (g) II. H2 (g) + O2 (g) → H2O2 (l) III. C (graphite) → C (diamond)   A. Only I B. Only II C. Only III D. I and II E. II and III
Which of the following does not have a standard enthalpy of formation equal to zero at 25°C and 1.0 atm? a) F2 (g)  b) Al (s) c) H2 (g) d) H2O (l)  e) They all have a standard enthalpy equal to zero.  
It is often argued that natural gas (CH4) is preferred to petroleum (which we will approximate as isooctane, C8H18) in generating energy in that it produces less CO 2. The balanced  combustion reactions for CH4 and C8H18  are given below. CH4(g)  +  2O2(g)  →  CO2(g)  +   2H2O(g) 2C8H18(g)  +  25O2(g)  →  16CO2(g)  +   18H2O(g) Using the following heats of formation, calculate Joules of energy generated per mole of CO2 produced for each combustion. Is methane better than petroleum in lowering CO2 production (in other words, does it produce more CO2 per joules of energy)? H2O(g)       ΔH°f = -241.83 kJ/mol                CO2(g)       ΔH°f = -395.51 kJ/mol CH4(g)       ΔH°f = -74.1 kJ/mol                    C8H18(g)   ΔH°f = -224.1 kJ/mol  
Calculate the enthalpy change (ΔH°rxn ) for the following reaction at 25°C. The value of ΔH°f in kJ/mol is given below.  2 Fe2O3(s) + 6 CO(g) → 4 Fe(s) + 6 CO2(g) A. −1380 kJ B. −49.6 kJ C. 541 kJ D. −3350 kJ E. −24.8 kJ
Consider the partial oxidation of ethane as shown in the following reaction:  C2H6(g) + O2(g) → 2CO(g) + 3H2(g)  Now calculate ΔH° for the partial oxidation of ethane. The enthalpies of formation for C2H6(g) and CO(g) are -84.68 kJ/mol and -110.5 kJ/mol, respectively. 
The decomposition of ZnCO3(s) into ZnO(s) and CO2(g) at constant pressure requires the addition of 71.5 kJ of heat per mole of ZnCO3. You may want to reference (Pages 177 - 178) Section 5.4 while completing this problem.Choose an enthalpy diagram for the reaction.
Acetylene (C2H2) and nitrogen (N2) both contain a triple bond, but they differ greatly in their chemical properties.Both N2 and C2H2 possess triple bonds with quite high bond enthalpies (Table 8.4 in the textbook). Calculate the enthalpy of hydrogenation per mole for both compounds: acetylene plus H2 to make methane, CH4; nitrogen plus H2 to make ammonia, NH3.
The standard enthalpies of formation of gaseous propyne (C3H4), propylene (C3H6), and propane (C3H8) are +185.4, +20.4, and -103.8 kJ/mol, respectively.Which is the most efficient fuel in terms of heat evolved per unit mass?
Acetylene (C2H2) and nitrogen (N2) both contain a triple bond, but they differ greatly in their chemical properties.Calculate the enthalpy of oxidation per mole for N2 and for C2H2 (the enthalpy of formation of N2O5(g) is 11.30 kJ/mol).
What is a standard state?
What is the value of the standard enthalpy of formation of an element in its most stable form?
Which is more stable at room temperature, a Cl2 molecule or two separate Cl atoms?
What is the energy difference between the Cl2 molecule and the separated atoms?
What is meant by the term standard conditions, with reference to enthalpy changes?
Write the chemical equation for the reaction whose enthalpy change is the standard enthalpy of formation of sucrose, C12H22O11(s), HfHf[{ m C_{12}H_{22}O_{11}}].
A gas-phase reaction was run in an apparatus designed to maintain a constant pressure. Write a balanced chemical equation for the reaction depicted.
Consider the two diagrams below. Based on (i), write an equation showing how HA is related to HB and HC.
Consider the two diagrams below. Based on (ii), write an equation relating HZ to the other enthalpy changes in the diagram.
Can you use an approach similar to Hesss law to calculate the change in internal energy, E, for an overall reaction by summing the E values of individual reactions that add up to give the desired overall reaction?
The complete combustion of ethanol, C2H5OH (l), to form H2O (g) and CO2 (g) at constant pressure releases 1235 kJ of heat per mole of C2H5OH.Write a balanced equation for this reaction.
Write an equation for the formation of NH3 (g) from its elements in their standard states.
Write an equation for the formation of CO2 (g) from its elements in their standard states.
Write an equation for the formation of Fe2O3 (s) from its elements in their standard states.
Write an equation for the formation of CH4 (g) from its elements in their standard states.
Write an equation for the formation of one mole of NO2 (g) from its elements in their standard states.
Write an equation for the formation one mole of MgCO3 (s) from its elements in their standard states. Write any reference to carbon as C(s).
Write an equation for the formation one mole of C2H4 (g) from its elements in their standard states. Write any reference to carbon as C(s).
Write an equation for the formation one mole of CH3OH(l) from its elements in their standard states. Write any reference to carbon as C(s).
What is meant by the term enthalpy of formation?
Thermodynamic Quantities for Selected Substances at 298.15 K Substance Hfo (kJ/mol) NO(g) 90.37 NO2(g) 33.84 N2O(g) 81.6 N2O4(g) 9.66 SO2(g) -296.9 SO3(g) -395.2 NaBr(s) -361.4 NaBr(aq) -360.6 Pb(NO3)2(s) -451.9 Pb(NO3)2(aq) -421.3 Write a balanced equation depicting the formation of one mole of NO2(g) from its elements in their standard states.
What is meant by the term standard enthalpy of formation?
Thermodynamic Quantities for Selected Substances at 298.15 K Substance Hfo (kJ/mol) NO(g) 90.37 NO2(g) 33.84 N2O(g) 81.6 N2O4(g) 9.66 SO2(g) -296.9 SO3(g) -395.2 NaBr(s) -361.4 NaBr(aq) -360.6 Pb(NO3)2(s) -451.9 Pb(NO3)2(aq) -421.3 Write a balanced equation depicting the formation of one mole of SO3(g) from its elements in their standard states.
Thermodynamic Quantities for Selected Substances at 298.15 K Substance Hfo (kJ/mol) NO(g) 90.37 NO2(g) 33.84 N2O(g) 81.6 N2O4(g) 9.66 SO2(g) -296.9 SO3(g) -395.2 NaBr(s) -361.4 NaBr(aq) -360.6 Pb(NO3)2(s) -451.9 Pb(NO3)2(aq) -421.3 Write a balanced equation depicting the formation of one mole of NaBr(s) from its elements in their standard states.
Thermodynamic Quantities for Selected Substances at 298.15 K Substance Hfo (kJ/mol) NO(g) 90.37 NO2(g) 33.84 N2O(g) 81.6 N2O4(g) 9.66 SO2(g) -296.9 SO3(g) -395.2 NaBr(s) -361.4 NaBr(aq) -360.6 Pb(NO3)2(s) -451.9 Pb(NO3)2(aq) -421.3 Write a balanced equation depicting the formation of one mole of Pb(NO3)2(s) from its elements in their standard states.
You may want to reference (Pages 187 - 190) Section 5.7 and (Pages 1088 - 1091) Appendix C in the textbook while completing this problem.Write a balanced chemical equation depicting the formation of one mole of H2O2(g) from its elements in their standard states.
You may want to reference (Pages 187 - 190) Section 5.7 and (Pages 1088 - 1091) Appendix C in the textbook while completing this problem.Write a balanced chemical equation depicting the formation of one mole of CaCO3(s) from its elements in their standard states.
You may want to reference (Pages 187 - 190) Section 5.7 and (Pages 1088 - 1091) Appendix C in the textbook while completing this problem.Write a balanced chemical equation depicting the formation of one mole of POCl3(l) from its elements in their standard states.
You may want to reference (Pages 187 - 190) Section 5.7 and (Pages 1088 - 1091) Appendix C in the textbook while completing this problem.Write a balanced chemical equation depicting the formation of one mole of C2H5OH(l) from its elements in their standard states.
What is the standard enthalpy change for a reaction?
What is the standard enthalpy of formation for a compound?
Consider the decomposition of liquid hydrogen peroxide (H2O2) to form water and oxygen.What is the heat of formation for hydrogen peroxide?
Consider the decomposition of liquid hydrogen peroxide (H2O2) to form water and oxygen.What is the heat of formation for liquid water?
Consider the decomposition of liquid hydrogen peroxide (H2O2) to form water and oxygen.What is the heat of formation for gaseous oxygen?
A gas-phase reaction was run in an apparatus designed to maintain a constant pressure. Using data from Appendix C in the textbook, determine H for the formation of one mole of the product.
Acetylene (C2H2) and nitrogen (N2) both contain a triple bond, but they differ greatly in their chemical properties.By referring to Appendix C in the textbook, look up the enthalpies of formation of acetylene and nitrogen. Which compound is more stable?
Use bond enthalpies in the table below to estimate H for each of the following reactions. Average Bond Enthalpies (kJ/mol) C-H 413 N-H 391 O-H 463 F-F 155 C-C 348 N-N 163 O-O 146 C=C 614 N-O 201 O=O 495 Cl-F 253 C-N 293 N-F 272 O-F 190 Cl-Cl 242 C-O 358 N-Cl 200 O-Cl 203 Br-F 237 C=O 799 N-Br 243 O-I 234 Br-Cl 218 C-F 485 H-H 436 Br-Br 193 C-Cl 328 H-F 567 C-Br 276 H-Cl 431 I-Cl 208 C-I 240 H-Br 366 I-Br 175 H-I 299 I-I 151
Use bond enthalpies in the table below to estimate H for each of the following reactions. Average Bond Enthalpies (kJ/mol) C-H 413 N-H 391 O-H 463 F-F 155 C-C 348 N-N 163 O-O 146 C=C 614 N-O 201 O=O 495 Cl-F 253 C-N 293 N-F 272 O-F 190 Cl-Cl 242 C-O 358 N-Cl 200 O-Cl 203 Br-F 237 C=O 799 N-Br 243 O-I 234 Br-Cl 218 C-F 485 H-H 436 Br-Br 193 C-Cl 328 H-F 567 C-Br 276 H-Cl 431 I-Cl 208 C-I 240 H-Br 366 I-Br 175 H-I 299 I-I 151
Use bond enthalpies in the table below to estimate H for each of the following reactions. Average Bond Enthalpies (kJ/mol) C-H 413 N-H 391 O-H 463 F-F 155 C-C 348 N-N 163 O-O 146 C=C 614 N-O 201 O=O 495 Cl-F 253 C-N 293 N-F 272 O-F 190 Cl-Cl 242 C-O 358 N-Cl 200 O-Cl 203 Br-F 237 C=O 799 N-Br 243 O-I 234 Br-Cl 218 C-F 485 H-H 436 Br-Br 193 C-Cl 328 H-F 567 C-Br 276 H-Cl 431 I-Cl 208 C-I 240 H-Br 366 I-Br 175 H-I 299 I-I 151
First launch the video. The video will show you the Smart Figure. After watching the video, answer the related follow-up question. You can watch the video again or reference the Smart Figure in the book(Pages 193 - 193) at any point. This figure shows the gas phase reaction between methane, CH4, and chlorine, Cl2 to produce methyl chloride, CH3Cl and hydrogen chloride, HCl. Using the average bond enthalpies in the table below, estimate the Hrxn for the analogous gas phase reaction between methane, CH4, and bromine, Br2, to produce methyl bromide, CH3Br, and hydrogen bromide, HBr. TABLE 5.4 Average Bond Enthalpies (kJ/mol) C-H 413 N-H 391 O-H 463 F-F 155 C-C 348 N-N 163 O-O 146 C=C 614 N-O 201 O=O 495 Cl-F 253 C-N 293 N-F 272 O-F 190 Cl-Cl 242 C-O 358 N-Cl 200 O-Cl 203 C=O 799 N-Br 243 O-I 234 Br-F 237 C-F 485 Br-Cl 218 C-Cl 328 H-H 436 Br-Br 193 C-Br 276 H-F 567 C-I 240 H-Cl 431 I-Cl 208 H-Br 366 I-Br 175 H-I 299 I-I 151
The hydrocarbons acetylene (C2 H2 ) and benzene (C6 H6 ) have the same empirical formula. Benzene is an "aromatic" hydrocarbon, one that is unusually stable because of its structure.Which has greater enthalpy, 3 mol of acetylene gas or 1 mol of liquid benzene?
Complete combustion of 1 mol of acetone (C3H6 O) liberates 1790 kJ: C3H6O(l) + 4 (g)3(g) + 3(l) Ho= - 1790Using this information together with the standard enthalpies of formation of O2(g), CO2(g), and H2O(l) from Appendix C, calculate the standard enthalpy of formation of acetone.
You may want to reference (Pages 187 - 190) Section 5.7 and (Pages 1088 - 1091) Appendix C in the textbook while completing this problem.For H2O2(g), find the value of Hf. (Use Appendix C in the textbook.)
You may want to reference (Pages 187 - 190) Section 5.7 and (Pages 1088 - 1091) Appendix C in the textbook while completing this problem.For CaCO3(s), find the value of Hf. (Use Appendix C in the textbook.)
You may want to reference (Pages 187 - 190) Section 5.7 and (Pages 1088 - 1091) Appendix C in the textbook while completing this problem.For POCl3(l), find the value of Hf. (Use Appendix C in the textbook.)
You may want to reference (Pages 187 - 190) Section 5.7 and (Pages 1088 - 1091) Appendix C in the textbook while completing this problem.For C2H5OH(l), find the value of Hf. (Use Appendix C in the textbook.)
Diethyl ether, C4H10O (l), a flammable compound that has long been used as a surgical anesthetic, has the structure CH3 - CH2 - O - CH2 - CH3 The complete combustion of 1 mol of C4H10O (l) to CO2 (g) and H2O (l) yields Ho= -2723.7 kJ.By using the information in this problem and data in the following table, calculate HfHf for diethyl ether.
Gasoline is composed primarily of hydrocarbons, including many with eight carbon atoms, called octanes. One of the cleanest-burning octanes is a compound called 2,3,4-trimethylpentane, which has the following structural formula. The complete combustion of one mole of this compound to CO 2(g) and H2O(g) leads to ΔH° = -5064.9 kJ/mol. (a) Write a balanced equation for the combustion of 1 mol of C8H18(l).
Write the formation reaction for sodium perchlorate (NaClO4).
Gasoline is composed primarily of hydrocarbons, including many with eight carbon atoms, called octanes. One of the cleanest-burning octanes is a compound called 2,3,4-trimethylpentane, which has the following structural formula. The complete combustion of one mole of this compound to CO 2(g) and H2O(g) leads to ΔH° = -5064.9 kJ/mol. (b) Write a balanced equation for the formation of C8H18(l) from its elements.
Gasoline is composed primarily of hydrocarbons, including many with eight carbon atoms, called octanes. One of the cleanest-burning octanes is a compound called 2,3,4-trimethylpentane, which has the following structural formula. The complete combustion of one mole of this compound to CO 2(g) and H2O(g) leads to ΔH° = -5064.9 kJ/mol. (c) By using the information in this problem and data in Table 5.3, calculate ΔHf° for 2,3,4-trimethylpentane. 
Part A Calculate the standard enthalpy change for the reaction 2A + B ⇌ 2C + 2D Use the following data: Substance ΔHf° (kJ/mol) A -235 B -381 C 197 D -477 Express your answer to three significant figures and include the appropriate units.   Part B For the reaction given in Part A, how much heat is absorbed when 3.70 mol of A reacts? Express your answer to three significant figures and include the appropriate units.
Naphthalene (C10H8) is a solid aromatic compound often sold as mothballs. The complete combustion of this substance to yield CO2(g) and H2O(/) at 25°C yields 5154 kJ/mol. (a) Write balanced equations for the formation of naphthalene from the elements and for its combustion.
Naphthalene (C10H8) is a solid aromatic compound often sold as mothballs. The complete combustion of this substance to yield CO2(g) and H2O(/) at 25°C yields 5154 kJ/mol. (b) Calculate the standard enthalpy of formation of naphthalene.
Given the data in the table below, what is ΔH°rxn ?4NH3(g) + 5O2(g) → 4NO(g) + 6H 2O(l)A) -1172 kJB) -150 kJC) - 1540 kJD) -1892 kJ
For a particular isomer of C8H18, the following reaction produces 5113.3 kJ of heat per mole of C8H18(g) consumed, under standard conditions.  C8H18 + 25/2(O2) → 8CO2 + 9H2O     ΔH= -5113.3 kJ What is the standard enthalpy of formation of this isomer of C8H18(g)?
Methanol (CH3OH) is used as a fuel in race cars. (b) Calculate the standard enthalpy change for the reaction, assuming H2O(g) as a product.
Consider the reaction of N2O5 at 25°C for which the following data are relevant:2 N2O5 (g)      ⇌       4 NO 2 (g) + O2 (g)What is the ΔH° for the reaction?A. 110.02 kJB. 21.86 kJC. -21.86 kJD. 155.20 kJE. -155.20 kJ
The following table lists some enthalpy of formation values for selected substances.Substance                ΔH° f (kJ/mol)NaOH(aq)                  -469.1MgCl2(s)                    -641.8NaCl(aq)                    -407.3Mg(OH)2(s)               -924.5H2O(l)                       -285.8Determine the enthalpy for this reaction:MgCl2(s) + 2NaOH(aq) → Mg(OH)2(s) + 2NaCl(aq)Express your answer in kilojoules per mole to four significant figures.
Does ΔHrxn for the reaction represented by the following equation equal the standard enthalpy of formation for CH3OH(I)? Why or why not? C(graphite) + 4 H(g) + O(g) → CH3OH(l)
The enthalpy of combustion of acetylene C 2H2 is described byC2H2 (g) + (5/2)O2 (g) ⇌ CO2 (g) + H2O (l)   Heat of Reaction (Rxn) = -1299kJ/molCalculate the enthalpy of formation of accetylene, given the following enthalpies of formation:Standard formation [CO2 (g)] = -393.5 kJ/molStandard formation [H2O (l)] = -285.8 kj/mol
Acetone, CH3COCH3, is a liquid solvent. The enthalpy change at 25 C and 1 atm for the complete burning of 1 mol of acetone in oxygen to give CO2(g) and H2O(l) is -1791kJ. Calculate the standard enthalpy of formation of acetone.
The standard enthalpy change for the formation of silver chloride from its elements is _______ than the enthalpy change for the formation of silver bromide.a) more exothermicb) less exothermicc) more endothermicd) less endothermic
What is the value of ΔH° for this reaction?C4H4(g) + 2H2(g) → C4H8(g)a) -158 kJb) -128 kJc) +128 kJd) +158 kJ
How many grams of methane [CH 4(g)] must be combusted to heat 1.00 kg of water from 25.0°C to 90.0°C, assuming H2O(/) as a product and 100% efficiency in heat transfer? 
For a particular isomer of C 8H18, the following reaction produces 5104.1 kJ of heat per mole of C8H18(g) consumed, under standard conditions. C8H18(g) + 25/2 O2(g) → 8 CO2(g) + 9 H2O(g)                 ΔH°rxn = -5104.1 kJ What is the standard enthalpy of formation of this isomer of C 8H18(g)?
The density of ethanol C2H5OH is .7893 g/mL. Find the enthalpy of combustion for exactly 1 L.
Given the data in the table below, calculate ΔH°rxn for the reactionCa(OH)2 + 2H3AsO4 → Ca(H2AsO4)2 + 2H2Oa) -4219b) -130.4c) -4519d) -76.4e) -744.9
What is the balanced chemical equation for the reaction used to calculate ΔH°f of MgCO3(s)?
A typical frostless refrigerator uses 655 kWh of energy per year in the form of electricity. Suppose that all of this electricity is generated at a power plant that burns coal containing 3.2% sulfur by mass and that all of the sulfur is emitted as SO2 when the coal is burned. If all of the SO2 goes on to react with rainwater to form H2SO4, what mass of H2SO4 does the annual operation of the refrigerator produce? (Hint: Assume that the remaining percentage of the coal is carbon and begin by calculating ΔH°rxn for the combustion of carbon.) 
Use the information in the table to calculate ΔH° in kilo joules for the photosynthesis of glucose (C6H12O6) and O2 from CO2 and liquid H2O, a reaction carried out by all green plants.
Glycine, C2H5O2N. is important for biological energy. The combustion reaction of glycine is given by the equation: 4C2H5O2N(s) + 9O2(g) → 8CO2(g) + 10H2O(l) + 2N2(g) ΔH°rxn = -3857 kJ. Given that ΔH°f[CO2(g)] = -393.5 kJ/mol and ΔH°f[H2O(I)] = -285.8 kJ/mol, calculate the enthalpy of formation of glycine. a) -537.2 kJ/mol b) -268.2 kJ/mol c) -2,149 kJ/mol d) 3,178 e) -964 kJ/mol
Which of the following substances have a standard heat of formation (ΔH  f°) of zero? i) Cl2(g) at 2 atm ii) C2H6 at standard conditions iii) O2(g) at 25.0 °C iv) 1 atm Fe at 1200 °C
For which of the following reactions is ΔH ∘rxn equal to ΔH∘f of the product(s)? You do not need to look up any values to answer this question. Check all that apply. i) SO(g) + ½O2(g) → SO2(g) ii) 2Na(s) + F2(g) → 2NaF(s) iii) Na(s) + ½F2(g) → NaF(s) iv) S(s) + O2(g) → SO2(g) v) Na(s) + ½F2(l) → NaF(s) vi) SO3(g) → ½O2(g) + SO2(g)
Using the standard enthalpies of formation, what is the standard enthalpy of reaction? CO(g) + H2O(g) → CO2(g) + H2(g)
The combustion reaction of ethane (C2H6(g)) is shown below:                2C 2H6(g) + 7O2(g) → 4CO2(g) + 6H2O(l) a) Calculate the heat released when 1.000 mole of ethane (C2H6(g)) is burned.       b) Calculate the enthalpy change per gram for the combustion of ethane (C 2H6(g)).
Enthalpy H is a measure of the energy content of a system at constant pressure. Chemical reactions involve changes in enthalpy, H, which can be measured and calculated:Hrxn = products m Hf - reactants n Hfwhere the subscript "rxn" is for "enthalpy of reaction" and "f" is for "enthalpy of formation" and m and n represent the appropriate stoichiometric coefficients for each substance.The following table lists some enthalpy of formation values for selected substances.Substance                                 Hf (kJ/mol)HCl(g)                                        -92Al(OH)3(s)                                 -1277H2O(l)                                        -285.8AlCl3(s)                                      -705.6H2O(g)                                       -241.8 Part ADetermine the enthalpy for this reaction: Al(OH)3(s) + 3HCl(g) → AlCl3(s) + 3H2O(l)Express your answer in kilojoules per mole to four significant figures. Part BConsider the reaction 2Al(OH)3(s) → Al2O3(s) + 3H2O(l) with enthalpy of reaction Hrxn = 21.00kJ/molWhat is the enthalpy of formation of Al 2O3(s)? Express your answer in kilojoules per mole to four significant figures.
Using the standard enthalpies of formation listed in Table 1, compute the standard enthalpy of reaction for the following reactions:
Use a standard enthalpies of formation table to determine the change in enthalpy for each of these reactions. i) NaOH(s) + HCI(g) → NaCI(s) + H 2O(g) ii) 2 CO(g) + O2(g) → 2 CO2(g)  
At one time, a common means of forming small quantities of oxygen gas in the laboratory was to heat KClO3:2 KClO3(s) → 2 KCl(s) + 3 O2(g)   ΔH = -89.4 kJFor this reaction, calculate ΔH for the formation of (a) 0.632 mol of O 2
At one time, a common means of forming small quantities of oxygen gas in the laboratory was to heat KClO3:2 KClO3(s) → 2 KCl(s) + 3 O 2(g)   ΔH = -89.4 kJFor this reaction, calculate ΔH for the formation of (b) 8.57 g of KCI.
Given the standard enthalpies of formation in the table below, calculate the standard enthalpy change (ΔH°) in KJ for the following reaction. CH4(g) + O3(g) → CO2(g) + 2H2O(g) a. -2979KJ b. 2979KJ c. -703KJ d. 703KJ  e. -853KJ
Calculate the enthalpy of reaction (in kJ) for 5.6 g of iron solid is reacted with aqueous Copper sulfate.
What is the balanced chemical equation for the reaction used to calculate the standard enthalpy of formation of SrCO3 (s)?
Use the standard enthalpies of formation in the table  CrO42- (aq) = -881.2 Cr2O72-(aq) = -1490.3 H+ (aq) = 0 H2O (l) = -285.8 to calculate ΔH for this reaction: 2CrO42- (aq) + 2H+(aq) → Cr2O72-(aq) + H2O (l)
Determine the enthalpy for this reaction: Ca(OH)2(s) + CO2(g) → CaCO3(s) + H2O(l) Enthalpy of formation for selected substances- CO2(g)                             ΔH   f∘= −393 kJ/mol Ca(OH)2(s)                      ΔH   f∘= −987 kJ/mol H2O(l)                              ΔH   f∘= −286 kJ/mol CaCO3(s)                        ΔH   f∘=  −1207 kJ/mol
For which should the standard heat of formation ΔH°f, be zero at 25°C? A) O3(g) B) O2(g) C) O(g) D) all the above
Use a standard enthalpies of formation table to determine the change in enthalpy for each of these reactions. i) CH4(g) + 2 O2(g) → CO2(g) + 2 H2O(l) ii) 2 H2S(g) + 3 O2(g) → 2 H2O(l) + 2 SO2(g) iii) 2 NO(g) + O2(g) → 2 NO2(g)
A city of 100,000 people uses approximately 1.0 x 1011 kJ of energy per day (an exothermic process). Suppose all of that energy comes from the combustion of liquid octane (C8H18). Use the given standard enthalpies of formation to find the ∆H for the combustion of octane and then determine how many kg of octane would be necessary to provide that amount of energy.                   C8H18   +   25/2 O2   →   8 CO2   +   9 H2O∆H for octane = -250.1 kJ/mol∆H for carbon dioxide = -393.5 kJ/mol∆H for water = -241.8 kJ/mol
 To which one of the following reactions occurring at 25°C does the symbol ΔH°f of HNO3(l) refer?a. H(g) + N(g) + O3(g) → HNO3(l)b. (1/2)H2(g) + (1/2)N2(g) + (3/2)O2(g) → HNO3(l)c. HNO3(l ) → (1/2)H2(g) + (1/2)N2(g) + (3/2)O2(g)d. HNO3(l) → H(g) + N(g) + 3O(g)e. H2(g) + N2(g) + O3(g) → HNO3(l)
Write balanced equations that describe the formation of the following compounds from elements in their standard states, and use Appendix C to obtain the values of their standard enthalpies of formation: (a) HBr(g)
 Write a balanced reaction for the combustion of ethylene, and find ΔH° formation of ethylene. C2H4(g). Given the following data:ΔH° of combustion of C2H4(g) = - 1411 kJ/molΔH° formation of CO2 (g) = - 393.5 kJ/molΔH° formation of H2O(I) = - 285.8 kJ/mol
Write balanced equations that describe the formation of the following compounds from elements in their standard states, and use Appendix C to obtain the values of their standard enthalpies of formation: (b) AgNO3(s)
Write balanced equations that describe the formation of the following compounds from elements in their stan·dard states, and use Appendix C to obtain the values of their standard enthalpies of formation: (c) Fe2O3 (s)
Write balanced equations that describe the formation of the following compounds from elements in their standard states, and use Appendix C to obtain the values of their standard enthalpies of formation: (d) CH3COOH(/).
Using values from Appendix C, calculate the value of ΔH° for each of the following reactions:(a) 4 HBr(g) + O2(g) → 2 H2O(/) + 2 Br2(/)
Using values from Appendix C, calculate the value of ΔH° for each of the following reactions:(b) 2 Na(OH)(s) + SO3(g) → Na2SO4(s) + H2O(g) 
Using values from Appendix C, calculate the value of ΔH° for each of the following reactions:(c) CH4(g) + 4 Cl2(g) → CCl4(l) + 4 HCI(g) 
Using values from Appendix C, calculate the value of ΔH° for each of the following reactions:(d) Fe2O3(s) + 6 HCI(g) → 2 FeCI3(s) + 3 H2O(g)
Calculate the approximate enthalpy change, ΔH rxn, for the combustion of methane:                           CH   4 + 2O2 → 2H2O + CO2Given that-ΔH for CH4 = -74.53 kJ/molΔH for O2 = 0 kJ/molΔH for H2O = -241.8 kJ/molΔH for CO2 = -393.5 kJ/mol
For a particular isomer of C8H18, the following reaction produces 5099.5 kJ of heat per mole of C8H18(g) consumed, under standard conditions.C8H18(g) + 25/2 O2(g) → 8 CO2(g) + 9 H2O(g)      ΔH(rxn) = -5099.5 kJ/Mol What is the standard enthalpy of formation of this isomer of C 8H18(g)?
Pentaborane-9, B5H9, will combust when exposed to oxygen into B2O3(s) and water at 25°C and 1 atm. Determine the energy in the form of heat released at constant pressure per gram of B5H9, given the following ΔH°f values: B5H9(l), 73.2 kJ•mol-1; B2O3(s), -1263.6 73.2 kJ•mol-1; H2O(l), -285.873.2 kJ•mol-1; H2O(g), -241.818 kJ•mol -1;a) -9000 kJ•g-1b) 145 kJ•g-1c) 8900 kJ•g-1d) -140 kJ•g-1e) -71 kJ•g-1
Complete combustion of 1 mol of acetone (C 3H6O) liberates 1790 kJ:C3H6O (l) + 4 O 2 (g) → 3 CO2 (g) + 3 H2O (l)     ΔH° = -1790 kJUsing this information together with data from Appendix C, calculate the enthalpy of formation of acetone. 
Determine the enthalpy for this reaction:Al(OH)3(s) + 3HCl(g) → AlCl3(s) + 3H2O(l)
Joseph Priestly prepared oxygen in 1774 by heating red mercury(II) oxide with sunlight focused through a lens. How much heat is required to decompose exactly 1 mole of red HgO(s) to Hg(l) and O2(g) under standard conditions?
How many kilojoules of heat will be released when exactly 1 mole of manganese, Mn, is burned to form Mn3O4(s) at standard state conditions?
How many kilojoules of heat will be released when exactly 1 mole of iron, Fe, is burned to form Fe2O3(s) at standard state conditions?
From the molar heats of formation in Appendix G, determine how much heat is required to evaporate one mole of water: H2O(l) ⟶ H2O(g)
In a coffee-cup calorimeter, 100.0 mL of 1.0 M NaOH and 100.0 mL of 1.0 M HCl are mixed. Both solutions were originally at 24.6°C. After the reaction, the final temperature is 31.3°C. Assuming that all the solutions have a density of 1.0 g/cm3 and a specific heat capacity of 4.18 J/°C ? g, calculate the enthalpy change for the neutralization of HCl by NaOH. Assume that no heat is lost to the surroundings or to the calorimeter.
The white pigment TiO2 is prepared by the reaction of titanium tetrachloride, TiCl 4, with water vapor in the gas phase: TiCl4(g) + 2H2O(g) ⟶ TiO2(s) + 4HCl(g).How much heat is evolved in the production of exactly 1 mole of TiO 2(s) under standard state conditions?
From the data in Table 5.2, determine which of the following fuels produces the greatest amount of heat per gram when burned under standard conditions: CO(g), CH4(g), or C2H2(g).
You may want to reference (Pages 248 - 284) Chapter 6 while completing this problem.Hydrogen and methanol have both been proposed as alternatives to hydrocarbon fuels. Use standard enthalpies of formation to calculate the amount of heat released per kilogram of methanol fuel.
You may want to reference (Pages 248 - 284) Chapter 6 while completing this problem.Hydrogen and methanol have both been proposed as alternatives to hydrocarbon fuels. To compare the energy of these fuels to that of octane (C8H18), calculate the energy released per kilogram of octane.
Among the substances that react with oxygen and that have been considered as potential rocket fuels are diborane [B2H6, produces B2O3(s) and H2O(g)], methane [CH4, produces CO2(g) and H2O(g)], and hydrazine [N2H4, produces N2(g) and H2O(g)]. On the basis of the heat released by 1.00 g of each substance in its reaction with oxygen, which of these compounds offers the best possibility as a rocket fuel? The ΔH°f of B2H6(g), CH4(g), and N2H4(l) may be found in Appendix G.
How much heat is produced when 1.25 g of chromium metal reacts with oxygen gas under standard conditions?
You may want to reference (Pages 248 - 284) Chapter 6 while completing this problem.Hydrogen and methanol have both been proposed as alternatives to hydrocarbon fuels. Use standard enthalpies of formation to calculate the amount of heat released per kilogram of hydrogen fuel.
When 10.00 g of phosphorus is burned in O2(g) to form P4O10(s), enough heat is generated to raise the temperature of 2960 g of water from 18.0˚C to 38.0˚C. Calculate the heat of formation of P4O10(s) under these conditions.
How much heat is released when 25.0 g of methane burns in excess O 2 to form gaseous CO2 and H2O?
The decomposition of hydrogen peroxide, H 2O2, has been used to provide thrust in the control jets of various space vehicles. Using the data in Appendix G, determine how much heat is produced by the decomposition of exactly 1 mole of H2O2 under standard conditions. 2H 2O2(l) ⟶ 2H2O(g) + O2(g)
A typical frostless refrigerator uses 655  kWh of energy per year in the form of electricity. Suppose that all of this electricity is generated at a power plant that burns coal containing 3.3% sulfur by mass and that all of the sulfur is emitted as SO2 when the coal is burned. If all of the SO2 goes on to react with rainwater to form H2SO4, what mass of H2SO4 is produced by the annual operation of the refrigerator? (Hint: Assume that the remaining percentage of the coal is carbon and begin by calculating ΔH˚rxn for the combustion of carbon.)
When backpacking in the wilderness, hikers often boil water to sterilize it for drinking. Suppose that you are planning a backpacking trip and will need to boil 36 L of water for your group. What volume of fuel should you bring? Assume each of the following: the fuel has an average formula of C7H16; 15% of the heat generated from combustion goes to heat the water (the rest is lost to the surroundings); the density of the fuel is 0.78 g/mL; the initial temperature of the water is 25.0 oC; and the standard enthalpy of formation of C7H16 is –224.4 kJ/mol.
Some automobiles and buses have been equipped to burn propane (C3H8). Compare the amounts of energy that can be obtained per gram of C3H8(g) and per gram of gasoline, assuming that gasoline is pure octane, C8H18(l). (See Example 7‑11.) Look up the boiling point of propane. What disadvantages are there to using propane instead of gasoline as a fuel?
The overall reaction in a commercial heat pack can be represented as:4Fe (s)+ 3 O2 (g) → 2Fe2O3              ΔH = -1652 kJc. How much heat is released when 1.00 g iron is reacted with excess O2?
Consider the following balanced thermochemical equation for a reaction sometimes used for H2S production:1/8S8 (s) + H2 (g) ⟶ H2S (g)                 ΔH = −20.2 kJWhat is ΔH when 2.6 mol of S 8 reacts?
Consider the following balanced thermochemical equation for a reaction sometimes used for H2S production:1/8S8 (s) + H2 (g) ⟶ H2S (g)                 ΔH = −20.2 kJWhat is ΔH when 25.0 g of S 8 reacts?
Ethylene oxide (EO) is prepared by the vapor-phase oxidation of ethylene. Its main uses are in the preparation of the antifreeze ethylene glycol and in the production of poly(ethylene terephthalate), which is used to make beverage bottles and fibers. Pure EO vapor can decompose explosively:Liquid EO has ΔH°f = −77.4 kJ/mol and ΔH° for its vaporization = 569.4 J/g. External heating causes the vapor to decompose at 10 bar and 93°C in a distillation column. What is the final temperature if the average specific heat capacity of the products is 2.5 J/g•°C?
When 1 mol of NO(g) forms from its elements, 90.29 kJ of heat is absorbed. What is ΔH when 3.50 g of NO decomposes to its elements?
When 1 mol of KBr(s) decomposes to its elements, 394 kJ of heat is absorbed. What is ΔH when 10.0 kg of KBr forms from its elements?
Deterioration of buildings, bridges, and other structures through the rusting of iron costs millions of dollars a day. Theactual process requires water, but a simplified equation is4Fe (s) + 3O2 (g) ⟶ 2Fe2O3 (s)             Δ H = −1.65 x 10 3 kJHow much heat is released when 0.250 kg of iron rusts?
The overall reaction in a commercial heat pack can be represented as:4Fe (s)+ 3 O2 (g) → 2Fe2O3              ΔH = -1652 kJd. How much heat is released when 10.0 g Fe and 2.00 g O2 are reacted?
The overall reaction in a commercial heat pack can be represented as:4Fe (s)+ 3 O2 (g) → 2Fe2O3              ΔH = -1652 kJb. How much heat is released when 1.00 mole of Fe2O3 is produced?
The overall reaction in a commercial heat pack can be represented as:4Fe (s)+ 3 O2 (g) → 2Fe2O3              ΔH = -1652 kJa. How much heat is released when 4.00 moles of iron are reacted with excess O2?
A mercury mirror forms inside a test tube as a result of the thermal decomposition of mercury(II) oxide:2HgO (s) ⟶ 2Hg (l ) + O 2 (g)        Δ H = 181.6 kJHow much heat is absorbed to decompose 555 g of the oxide?
A mercury mirror forms inside a test tube as a result of the thermal decomposition of mercury(II) oxide: 2HgO (s) ⟶ 2Hg (l ) + O 2 (g)        Δ H = 181.6 kJIf 275 kJ of heat is absorbed, how many grams of Hg form?
Sucrose (C12H22O11, table sugar) is oxidized in the body by O 2 via a complex set of reactions that produces CO2(g) and H2O(g) and releases 5.64 x 103 kJ/mol sucrose.How much heat is released per gram of sucrose oxidized?
What is the heat of combustion of ethane, C 2H6, in kilojoules per mole of ethane?
Does the standard enthalpy of formation of H 2O(g) differ from ΔH° for the reaction2H2(g) + O2(g) ⟶ 2H2O(g)?
Consider the decomposition of liquid hydrogen peroxide (H2O2) to form water and oxygen. Write the balanced chemical equation that corresponds to the ΔH˚f value you looked up for hydrogen peroxide.
Consider the decomposition of liquid hydrogen peroxide (H2O2) to form water and oxygen. Write the balanced chemical equation that corresponds to the ΔH˚f value you looked up for liquid water.
Consider the decomposition of liquid hydrogen peroxide (H2O2) to form water and oxygen. Write the balanced chemical equation that corresponds to the ΔH˚f value you looked up for gaseous oxygen.
Kerosene, a common space-heater fuel, is a mixture of hydrocarbons whose “average” formula is C12H26.a) Write a balanced equation, using the simplest whole-number coefficients, for the complete combustion of kerosene to gases.
Stearic acid (C18H36O2) is a fatty acid, a molecule with a long hydrocarbon chain and an organic acid group (COOH) at the end. It is used to make cosmetics, ointments, soaps, and candles and is found in animal tissue as part of many saturated fats. In fact, when you eat meat, you are ingesting some fats containing stearic acid.Write a balanced equation for the combustion of stearic acid to gaseous products.
Consider the following equations:3A + 6B → 3D    ΔH = -403 kJ/molE + 2F → A         ΔH = -105.2 kJ/molC → E + 3D        ΔH = 64.8 kJ/molSuppose the first equation is reversed and multiplied by 16 , the second and third equations are divided by 2, and the three adjusted equations are added. What is the net reaction and what is the overall heat of this reaction?
Write a balanced equation and draw an enthalpy diagram for formation of 1 mol of sodium chloride from its elements (heat is released).
Write a balanced equation and draw an enthalpy diagram for vaporization of liquid benzene.
Write a balanced equation and draw an enthalpy diagram for combustion of 1 mol of liquid methanol (CH3OH).
Write a balanced equation and draw an enthalpy diagram for formation of 1 mol of NO 2 from its elements (heat is absorbed).
Write a balanced equation and draw an enthalpy diagram for sublimation of dry ice [conversion of CO2(s) directly to CO2(g)].
Write a balanced equation and draw an enthalpy diagram for reaction of 1 mol of SO 2 with O2.
What is the balanced chemical equation for the reaction used to calculate Δ H∘f of CaCO3(s)? If fractional coefficients are required, enter them as a fraction (i.e. 1/3). Indicate the physical states using the abbreviation (s), (l), or (g) for solid, liquid, or gas, respectively without indicating allotropes. Use (aq) for aqueous solution. Express your answer as a chemical equation.
Choose the reaction that represents ΔH°f for Ca(NO3)2a. Ca2+(aq) + 2NO3-(aq) → Ca(NO3)2(aq)b. Ca(s) + 2N(g) + 6O(g) → Ca(NO3)2(s)c. Ca(NO3)2(aq) → Ca2+(aq) 2NO3-(aq)d. Ca(s) + N2(g) + 3O2(g) → Ca(NO3)2(s)e. Ca(NO3)2(s) → Ca(s) + N2(g) + 3O2(g)
For which of the following reactions is ΔH∘rxn equal to ΔH∘f of the product(s)? You do not need to look up any values to answer this question. Check all that apply. a) Li(s)+12F2(g)→LiF(s) b) Li(s)+12F2(l)→LiF(s) c) H2O2(g)→12O2(g)+H2O(g) d) 2H2(g)+O2(g)→2H2O(g) e) 2Li(s)+F2(g)→2LiF(s) f) H2(g)+12O2(g)→H2O(g)
When 1 mol of NO(g) forms from its elements, 90.29 kJ of heat is absorbed. Write a balanced thermochemical equation.
The following scenes represent a gaseous reaction between compounds of nitrogen (blue) and oxygen (red) at 298 K:Write a balanced equation and calculate ΔH°rxn.
You may want to reference (Page 277) Section 6.9 while completing this problem.The standard enthalpy of formation for glucose, C6H12O6(s), is –1273.3 kJ/mol. What is the correct formation equation corresponding to this ΔH˚f?
When 1 mol of KBr(s) decomposes to its elements, 394 kJ of heat is absorbed. Write a balanced thermochemical equation.
Give the definition of the standard enthalpy of formation for a substance. Write separate reactions for the formation of NaCl, H2O, C6H12O6, and PbSO4 that have ΔH° values equal to ΔHf° for each compound.
Most ethylene (C2H4), the starting material for producing polyethylene, comes from petroleum processing. It also occurs naturally as a fruit-ripening hormone and as a component of natural gas. The heat transferred during combustion of C2H4 is −1411 kJ/mol. Write a balanced thermochemical equation.
Sucrose (C12H22O11, table sugar) is oxidized in the body by O 2 via a complex set of reactions that produces CO2(g) and H2O(g) and releases 5.64 x 103 kJ/mol sucrose.Write a balanced thermochemical equation for the overall process.
For which of the following reactions is ΔH°rxn equal to ΔH°f of the product(s)? Select all that apply. H2(g) + 12O2(g) → H2O(g) 2Li(s) + Cl2(g) → 2LiCl(s) Li(s) + 12Cl2(l) → LiCl(s) 2H2(g) + O2(g) → 2H2O(g) H2O2(g) → 12O2(g)+H2O(g) Li(s)+12Cl2(g)→LiCl(s)
If the standard enthalpy of combustion of ethanol (C 2H5OH(l)) at 298 K is −1368 kJ.mol−1, calculate the standard enthalpy of formation of ethanol. The standard enthalpies of formation of carbon dioxide and liquid water are −393.51 and −285.83 kJ.mol−1, respectively.a. −688.7 kJ.mol−1b. +688.7 kJ.mol−1c. −344.3 kJ.mol−1d. −276.5 kJ.mol−1e. +276.5 kJ.mol−1
The net change during photosynthesis involves CO 2 and H2O forming glucose (C6H12O6) and O2. Chlorophyll absorbs light in the 600–700 nm region. Write a balanced thermochemical equation for formation of 1.00 mol of glucose.
Write reactions for which the enthalpy change will bea. ΔHf° for solid aluminum oxide.
Write reactions for which the enthalpy change will beb. the standard enthalpy of combustion of liquid ethanol, C2H5OH(l).
Write reactions for which the enthalpy change will bef. the enthalpy of solution of solid ammonium bromide.
Write reactions for which the enthalpy change will bee. the enthalpy of combustion of liquid benzene, C6H6(l).
Write reactions for which the enthalpy change will bed. ΔHf° for gaseous vinyl chloride, C2H3Cl(g).
Write reactions for which the enthalpy change will bec. the standard enthalpy of neutralization of sodium hydroxidesolution by hydrochloric acid.c. the standard enthalpy of neutralization of sodium hydroxide solution by hydrochloric acid.
Use the ΔH°f and ΔH°rxn information provided to calculate ΔH°f for IF.IF7(g) + I2(g) → IF5(g) + 2IF(g)                        ΔH°rxn = -89kJ                ΔH°f(kJ/mol)IF7(g)              -941IF5(g)              -840a. 24kJ/molb. 101 kJ/molc. -95 kJ/mold. -190 kJ/mole. -146 kJ/mol
Using the standard enthalpies of formation, what is the standard enthalpy of reaction? CO(g) +H2O(g) → CO2 g) + H2(g)  
a. Write a balanced equation for the combustion of ethanol, C 2H5OH(l) in oxygen. Carbon dioxide is produced in the gaseous state, water in the liquid state. b.The standard heat of combustion of ethanol is -1367 kJ/mol. Calculate the standard heat of formation of ethanol, ΔH.
What is the heat of combustion of ethane, C2H6, in kilojoules per mole of ethane?
Calculate the standard enthalpy change for the reaction: 2A+B ⇌ 2C+2D Use the following data: Substance ΔH∘f (kJ/mol) A -261 B -417 C 189 D -503
Even though so much energy is required to form a metal cation with a 2+ charge, the alkaline earth metals form halides with the general formula MX2, rather than MX.(b) Is MgCl favored energetically relative to Mg and Cl 2? Explain.
Use the values of ΔHf° in Appendix 4 to calculate ΔH° for the following reactions
How can you calculate ΔH˚rxn from tabulated standard enthalpies of formation?
Use the values of ΔHf° in Appendix 4 to calculate ΔH° for the following reactionsb. SiCl4 (l) + 2H2O(l) → SiO2 (s) + 4HCl (aq)
Use the values of ΔHf° in Appendix 4 to calculate ΔH° for the following reactionsc. MgO (s) + H2O (l) → Mg(OH)2 (s)
Calculate ΔH°rxn for the following:2H2S(g) + 3O2(g) ⟶ 2SO2(g) + 2H2O(g)
Calculate ΔH°rxn for the following:CH4(g) + Cl2(g) ⟶ CCl4(l) + HCl(g)       [unbalanced]
Calculate ΔH°rxn for the following:SiO2(s) + 4HF(g) ⟶ SiF4(g) + 2H2O(l)
Using the data in Appendix G, calculate the standard enthalpy change for the following reaction:(a) N2(g) + O2(g) ⟶ 2NO(g)
Calculate ΔH°rxn for the following:C2H6(g) + O2(g) ⟶ CO2(g) + H2O(g)          [unbalanced]
Copper(I) oxide can be oxidized to copper(II) oxide:Cu2O(s) + 1/2O2(g) ⟶ 2CuO(s)              ΔH°rxn = −146.0 kJGiven ΔH°f of Cu2O(s) = −168.6 kJ/mol, find ΔH°f of CuO(s).
Acetylene burns in air according to the following equation:C2H2(g) + 5/2O2(g) ⟶ 2CO2(g) + H2O(g)          ΔH°rxn = −1255.8 kJGiven ΔH°f of CO2(g) = −393.5 kJ/mol and ΔH°f of H2O(g) = −241.8 kJ/mol, find ΔH°f of C2H2(g).
Using the data in Appendix G, calculate the standard enthalpy change for the following reaction:(b) Si(s) + 2Cl2(g) ⟶ SiCl4(g)
Use the values of ΔHf° in Appendix 4 to calculate ΔH° for the following reactionsb. Ca3(PO4)2 (s) + 3H2SO4 (l) → 3CaSO4 (s) + 2H3PO4(l)
Use the values of ΔHf° in Appendix 4 to calculate ΔH° for the following reactionsc. NH3 (g) + HCl (g) → NH4Cl (s)
Using the data in Appendix G, calculate the standard enthalpy change for the following reaction:(c) Fe2O3 (s) + 3H2(g) ⟶ 2Fe(s) + 3H2O(l)
Using the data in Appendix G, calculate the standard enthalpy change for the following reaction:(d) 2LiOH(s) + CO2(g) ⟶ Li2CO3(s) + H2O(g)
The common lead-acid car battery produces a large burst of current, even at low temperatures, and is rechargeable. The reaction that occurs while recharging a “dead” battery is2PbSO4(s) + 2H2O(l) ⟶ Pb(s) + PbO2(s) + 2H2SO4(l)Calculate ΔH°rxn.
Stearic acid (C18H36O2) is a fatty acid, a molecule with a long hydrocarbon chain and an organic acid group (COOH) at the end. It is used to make cosmetics, ointments, soaps, and candles and is found in animal tissue as part of many saturated fats. In fact, when you eat meat, you are ingesting some fats containing stearic acid.Calculate ΔH°rxn for this combustion (ΔH°f of C18H36O2 = −948 kJ/mol).
The Ostwald process for the commercial production of nitric acid from ammonia and oxygen involves the following steps:4NH3 (g) + 5O2 (g) → 4NO (g) + 6 H2O (g)2NO(g) + O2 (g) → 2NO2 (g)3NO2 (g) + H2O (l) → 2HNO3 (aq) + NO (g)a. Use the values of ΔH°f in Appendix 4 to calculate the value of ΔH° for each of the preceding reactions.
Kerosene, a common space-heater fuel, is a mixture of hydrocarbons whose “average” formula is C12H26.b) If ΔH°rxn = −1.50 x 104 kJ for the combustion equation, determine ΔH°f of kerosene.
Using the data in Appendix G, calculate the standard enthalpy change for the following reaction:(a) Si(s) + 2F2(g) ⟶ SiF4(g)
Using the data in Appendix G, calculate the standard enthalpy change for the following reaction:(b) 2C(s) + 2H2(g) + O2(g) ⟶ CH3CO2 H(l)
Silicon tetrachloride is produced annually on the multikiloton scale and used in making transistor-grade silicon. It can be produced directly from the elements (reaction 1) or, more cheaply, by heating sand and graphite with chlorine gas (reaction 2). If water is present in reaction 2, some tetrachloride may be lost in an unwanted side reaction (reaction 3):(1) Si(s) + 2Cl2(g) ⟶ SiCl4(g)(2) SiO2(s) + 2C(graphite) + 2Cl2(g) ⟶ SiCl4(g) + 2CO(g)(3) SiCl4(g) + 2H2O(g) ⟶ SiO2(s) + 4HCl(g)        ΔH°rxn = −139.5 kJUse reaction 3 to calculate the standard enthalpies of reaction of reactions 1 and 2.
Using the data in Appendix G, calculate the standard enthalpy change for the following reaction:(c) CH4(g) + N2(g) ⟶ HCN(g) + NH 3(g);
Hydrazine (N2H4) is a fuel used by some spacecraft. It is normally oxidized by N2O4 according to the following equation: N2H4(l) + N2O4(g) → 2 N2O(g) + 2 H2O(g). Calculate ΔH˚rxn for this reaction using standard enthalpies of formation.
Silicon tetrachloride is produced annually on the multikiloton scale and used in making transistor-grade silicon. It can be produced directly from the elements (reaction 1) or, more cheaply, by heating sand and graphite with chlorine gas (reaction 2). If water is present in reaction 2, some tetrachloride may be lost in an unwanted side reaction (reaction 3):(1) Si(s) + 2Cl2(g) ⟶ SiCl4(g)(2) SiO2(s) + 2C(graphite) + 2Cl2(g) ⟶ SiCl4(g) + 2CO(g)(3) SiCl4(g) + 2H2O(g) ⟶ SiO2(s) + 4HCl(g)        ΔH°rxn = −139.5 kJWhat is the standard enthalpy of reaction for a fourth reaction that is the sum of reactions 2 and 3?
Use standard enthalpies of formation to calculate ΔH˚rxn for the following reaction: C2H4(g) + H2(g) → C2H6(g){ m{C}}_2 { m{H}}_4 (g); + ;{ m{H}}_2 (g); ightarrow ;{ m{C}}_2 { m{H}}_6 (g)
Use standard enthalpies of formation to calculate ΔH˚rxn for the following reaction: CO(g) + H2O(g) → H2(g) + CO2(g){ m{CO(}}g); + ;{ m{H}}_2 { m{O(}}g); ightarrow ;{ m{H}}_2 (g); + ;{ m{CO}}_2 (g)
Water gas, a mixture of H2 and CO, is an important industrial fuel produced by the reaction of steam with red hot coke, essentially pure carbon: C(s) + H2O(g) ⟶ CO(g) + H2(g).Assuming that coke has the same enthalpy of formation as graphite, calculate ΔH°298 for this reaction.
Use standard enthalpies of formation to calculate ΔH˚rxn for the following reaction: 3 NO2(g) + H2O(l) → 2 HNO3(aq) + NO(g)3{ m{ NO}}_2 (g); + ;{ m{H}}_2 { m{O(}}l); ightarrow ;2{ m{ HNO}}_3 (aq); + ;{ m{NO(}}g)
Use standard enthalpies of formation to calculate ΔH˚rxn for the following reaction: Cr2O3(s) + 3 CO(g) → 2 Cr(s) + 3 CO2(g){ m{Cr}}_2 { m{O}}_3 (s); + ;3{ m{ CO(}}g); ightarrow ;2{ m{ Cr(}}s); + ;3{ m{ CO}}_2 (g)
Water gas, a mixture of H2 and CO, is an important industrial fuel produced by the reaction of steam with red hot coke, essentially pure carbon: C(s) + H2O(g) ⟶ CO(g) + H2(g).Methanol, a liquid fuel that could possibly replace gasoline, can be prepared from water gas and additional hydrogen at high temperature and pressure in the presence of a suitable catalyst: 2H2(g) + CO(g) ⟶ CH3OH(g). Under the conditions of the reaction, methanol forms as a gas. Calculate ΔH°298 for this reaction and for the condensation of gaseous methanol to liquid methanol.
During photosynthesis, plants use energy from sunlight to form glucose, C6H12O6(s), and oxygen from carbon dioxide and water. Calculate ΔH˚rxn for photosynthesis.
The standard enthalpy of combustion of ethene gas, C2H4(g), is -1411.1 kJ/mol at 298 K. Given the following enthalpies of formation, calculate ΔHf° for C2H4(g).CO2 (g)          -393.5 kJ/molH2O (l)            -285.8 kJ/mol
Ethanol can be made from the fermentation of crops and has been used as a fuel additive to gasoline. Calculate ΔH˚rxn for the combustion of ethanol.
Using the data in Appendix G, calculate the standard enthalpy change for the following reaction:(d) CS2(g) + 3Cl2(g) ⟶ CCl4(g) + S2Cl2(g)
Top fuel dragsters and funny cars burn nitromethane as fuel according to the following balanced combustion equation: 2 CH3NO2(l) + 3/2 O2(g) → 2 CO2(g) + 3 H2O(l) + N2(g), ΔH˚rxn = –1418 kJ. The standard enthalpy of combustion for nitromethane is –709.2 kJ/mol. Calculate the standard enthalpy of formation (ΔH˚f) for nitromethane.
The enthalpy of combustion of solid carbon to form carbon dioxide is -393.7 kJ/mol carbon, and the enthalpy of combustion of carbon monoxide to form carbon dioxide is -283.3 kJ/mol CO. Use these data to calculate ΔH for the reaction2C (s) + O2 (g) → 2CO (g) 
You may want to reference (Pages 277 - 280) Section 6.9 while completing this problem.The explosive nitroglycerin (C3H5N3O9) decomposes rapidly upon ignition or sudden impact according to the following balanced equation: 4 C3H5N3O9(l) → 12 CO2(g) + 10 H2O(g) + 6 N2(g) + O2(g), ΔH˚rxn = –5678 kJ. Calculate the standard enthalpy of formation ( H˚f) for nitroglycerin.
In the early days of automobiles, illumination at night was provided by burning acetylene, C2H2. Though no longer used as auto headlamps, acetylene is still used as a source of light by some cave explorers. The acetylene is (was) prepared in the lamp by the reaction of water with calcium carbide, CaC2: CaC2(s) + 2H2O(l) ⟶ Ca(OH)2(s) + C2H2(g)Calculate the standard enthalpy of the reaction. The ΔH°f of CaC2 is −15.14 kcal/mol.
Methanol (CH3OH) has been suggested as a fuel to replace gasoline. Find ΔH˚rxn for the combustion of methanol.
Combustion reactions involve reacting a substance with oxygen. When compounds containing carbon and hydrogen are combusted, carbon dioxide and water are the products. Using the enthalpies of combustion for C4H4 (-2341 kJ/mol), C4H8 (-2755 kJ/mol), and H2 (-286 kJ/mol), calculate ΔH for the reaction C4H4 (g) + 2H2 (g)  → C4H8 (g) 
Ethanol, C2H5OH, is used as a fuel for motor vehicles, particularly in Brazil.Write the balanced equation for the combustion of ethanol to CO 2(g) and H2O(g), and, using the data in Appendix G, calculate the enthalpy of combustion of 1 mole of ethanol.
Water gas is produced from the reaction of steam with coal:C(s) + H2O (g) → H2 (g) + CO (g)Assuming that coal is pure graphite, calculate ΔH° for this reaction.
Use standard enthalpies of formation to calculate the standard change in enthalpy for the melting of ice. (The ΔH˚f for H2O(s) for is –291.8 kJ/mol{{ m{kJ}}}/{{ m{mol}}}).
The following reaction can be used to prepare samples of metals. Determine the enthalpy change under standard state condition.(a) 2Ag2O(s) ⟶ 4Ag(s) + O2(g)
Palmitic acid (C16H32O2) is a dietary fat found in beef and butter. The caloric content of palmitic acid is typical of fats in general. Calculate the standard enthalpy of combustion for palmitic acid. The standard enthalpy of formation of palmitic acid –208kJ/mol.
Calculate the standard enthalpy of combustion of sucrose. The standard enthalpy of formation of sucrose is –2226.1kJ/mol.
Calculate ΔH° for each of the following reactions, which occur in the atmosphere.c. SO3 (g) + H2O (l) → H2SO4 (aq)
Ethanol, C2H5OH, is used as a fuel for motor vehicles, particularly in Brazil.Assuming that an automobile’s mileage is directly proportional to the heat of combustion of the fuel, calculate how much farther an automobile could be expected to travel on 1 L of gasoline than on 1 L of ethanol. Assume that gasoline has the heat of combustion and the density of n–octane, C8H18 (ΔH°f = −208.4 kJ/mol; density = 0.7025 g/mL).
The following reaction can be used to prepare samples of metals. Determine the enthalpy change under standard state condition.(b) SnO(s) + CO(g) ⟶ Sn(s) + CO2(g)
Calculate ΔH° for each of the following reactions, which occur in the atmosphere.a. C2H4 (g) + O3 (g) → CH3CHO (g) + O2 (g)
Electric generating plants transport large amounts of hot water through metal pipes, and oxygen dissolved in the water can cause a major corrosion problem. Hydrazine (N2H4) added to the water prevents this problem by reacting with the oxygen:N2H4(aq) + O2(g) ⟶ N2(g) + 2H2O(l)About 4 x 107 kg of hydrazine is produced every year by reacting ammonia with sodium hypochlorite in the Raschig process:2NH3(aq) + NaOCl(aq) ⟶ N2H4(aq) + NaCl(aq) + H2O(l)    ΔH°rxn = −151 kJIf ΔH°f of NaOCl(aq) = −346 kJ/mol, find ΔH°f of N2H4(aq).
Ethylene, C2H2, a byproduct from the fractional distillation of petroleum, is fourth among the 50 chemical compounds produced commercially in the largest quantities. About 80% of synthetic ethanol is manufactured from ethylene by its reaction with water in the presence of a suitable catalyst. C2H4(g) + H2O(g) ⟶ C2H5OH(l) Using the data in the table in Appendix G, calculate ΔH° for the reaction.
Under certain nonstandard conditions, oxidation by O2(g) of 1 mol of SO2(g) to SO3(g) absorbs 89.6 kJ. The heat of formation of SO3(g) is –204.1 kJ/mol under these conditions. Find the heat of formation of SO2(g).
The following reaction can be used to prepare samples of metals. Determine the enthalpy change under standard state condition.(c) Cr2O3(s) + 3H2(g) ⟶ 2Cr(s) + 3H 2O(l)
Calculate ΔH° for each of the following reactions, which occur in the atmosphere.b. O3 (g) + NO (g) → NO2 (g) + O2 (g) 
Calculate ΔH° for each of the following reactions, which occur in the atmosphere.d. 2NO (g) + O2 (g) → 2NO2 (g)
The following reaction can be used to prepare samples of metals. Determine the enthalpy change under standard state condition.(d) 2Al(s) + Fe2O3(s) ⟶ Al2O3(s) + 2Fe(s)
The ΔHf˚ of TiI3(s) is –328 kJ/mol and the ΔH˚ for the reaction Ti(s) + 3 I2(g) → 2 TiI3(s) for the reaction is –839 kJ{ m kJ}. Calculate the ΔH of sublimation of I2(s), which is a solid at 25˚C.
Propane, C3H8, is a hydrocarbon that is commonly used as a fuel.The heat of combustion of propane is −2,219.2 kJ/mol. Calculate the heat of formation, ΔH°f of propane given that ΔH°f of H2O(l) = −285.8 kJ/mol and ΔH°f of CO2(g) = −393.5 kJ/mol.
Calculate the enthalpy of combustion of propane, C3H8(g), for the formation of H2O(g) and CO2(g). The enthalpy of formation of propane is −104 kJ/mol.
Calculate the enthalpy of combustion of butane, C 4H10(g) for the formation of H2O(g) and CO2(g). The enthalpy of formation of butane is −126 kJ/mol.
Consider the following balanced thermochemical equation for a reaction sometimes used for H2S production:1/8S8 (s) + H2 (g) ⟶ H2S (g)                 ΔH = −20.2 kJWhat is ΔH for the reverse reaction?
In winemaking, the sugars in grapes undergo fermentation by yeast to yield CH3CH2OH and CO2. During cellular respiration (combustion), sugar and ethanol yield water vapor and CO2.a) Using C6H12O6 for sugar, calculate ΔH°rxn of fermentation and of respiration.
You may want to reference (Pages 382 - 416) Chapter 9 while completing this problem.The table below shows the average bond energies for some common bonds among carbon, hydrogen, and oxygen.BondBond energy(kJ/mol)C - C347C - H414C - O360C = O799H - H436H - O464O - O142O = O498Calculate ΔHrxn for the combustion of octane by using enthalpies of formation from the transition above.
Three of the reactions that occur when the paraffin of a candle (typical formula C21H44) burns are as follows:(1) Complete combustion forms CO2 and water vapor.(2) Incomplete combustion forms CO and water vapor.(3) Some wax is oxidized to elemental C (soot) and water vapor.Find ΔH°rxn of each reaction (ΔH°f of C21H44 = −476 kJ/mol; use graphite for elemental carbon).
Consider the following balanced thermochemical equation for the decomposition of the mineral magnesite:MgCO3 (s) ⟶ MgO (s) + CO2 (g)                         ΔH = 117.3 kJWhat is ΔH for the reverse reaction?
Ethylene oxide (EO) is prepared by the vapor-phase oxidation of ethylene. Its main uses are in the preparation of the antifreeze ethylene glycol and in the production of poly(ethylene terephthalate), which is used to make beverage bottles and fibers. Pure EO vapor can decompose explosively:Liquid EO has ΔH°f = −77.4 kJ/mol and ΔH° for its vaporization = 569.4 J/g. Calculate ΔH°rxn for the gas-phase reaction.
You may want to reference (Page 277) Section 6.9 while completing this problem.Use standard enthalpies of formation to determine ΔH˚rxn for the reaction: Fe2O3(s) + 3 CO(g) → 2 Fe(s) + 3 CO2(g).
Dry ice is solid carbon dioxide. Instead of melting, solid carbon dioxide sublimes according to the equation: CO2(s) → CO2(g). When dry ice is added to warm water, heat from the water causes the dry ice to sublime more quickly. The evaporating carbon dioxide produces a dense fog often used to create special effects. In a simple dry ice fog machine, dry ice is added to warm water in a Styrofoam cooler. The dry ice produces fog until it evaporates away, or until the water gets too cold to sublime the dry ice quickly enough. Suppose that a small Styrofoam cooler holds 15.0 L of water heated to 86 °C. Use standard enthalpies of formation to calculate the change in enthalpy for dry ice sublimation. (The ΔH˚f for CO2(s) is –427.4 kJ/mol{ m{kJ}}/{ m{mol}})
The ΔH for the oxidation of sulfur in the gas phase to SO3 is -204 kJ/mol and for the oxidation of SO2 to SO3 is 89.5 kJ/mol.Find the enthalpy of formation of SO2 under these conditions.
You may want to reference (Pages 277 - 280) Section 6.9 while completing this problem.Pentane (C5H12) is a component of gasoline that burns according to the following balanced equation: C5H12(l) + 8 O2(g) → 5 CO2(g) + 6 H2O(g). Calculate Δ˚Hrxn for this reaction using standard enthalpies of formation. (The standard enthalpy of formation of liquid pentane is –146.8 kJ/mol{{ m{kJ}}}/{{ m{mol}}}.)
You may want to reference (Pages 277 - 280)Section 6.9 while completing this problem.Use standard enthalpies of formation to calculate ΔH˚rxn for the following reaction: C(s) + H2O(g) → CO(g) + H2(g){ m{C(}}{ m s}) + { m{H}}_2 { m{O(}}{ m g}) ightarrow { m{CO(}}{ m g}) + { m{H}}_2 ({ m g})
You may want to reference (Pages 277 - 280)Section 6.9 while completing this problem.Use standard enthalpies of formation to calculate ΔH˚rxn for the following reaction: 2 H2S(g) + 3 O2(g) → 2 H2O(l) + 2 SO2(g) 2{ m{ H}}_2 { m{S(}}{ m g}) + 3{ m{ O}}_2 ({ m g}) ightarrow 2{ m{ H}}_2 { m{O(}}{ m l}) + 2{ m{ SO}}_2 ({ m g})
Consider the following balanced reaction: 2A 2 + B --> C + 2D What is the enthalpy of reaction if the enthalpy of formation of the compounds is given as A 2 = -15.92 kJ/mol; B = 19.43 kJ/mol: C = 10.21 kJ/mol; D = 10.06 kJ/mol. Record your answer in scientific notation using 3 significant figures.
2H2S(g) + 3O2(g) --> 2SO2(g) + 2H2O(g)Calculate the ∆Hrxn
For a particular isomer of C8H18, the following reaction produces 5093.7 kJ of heat per mole of C8H18 (g) consumed, under standard conditions. C8H18 (g) + 25/2O2 (g) → 8CO2 (g)      ΔH°rxn = - 5093.7 kJ What is the standard enthalpy of formation of this isomer of C8H18?
Calculate ΔH°rxn for the combustion of C2H4(g) from the thermodynamic data in your text.C2H4(g) + 4 O2(g) → 2 CO2(g) + 2 H2O(I) ΔH °rxn = ???•-1411.1 kJ•-1358.4 kJ•-1305.9 kJ•+1305.9 kJ•+1411.1 kJ
Use average bond energies to estimate ΔH° for the following reaction: CH4 (g) + 2O2 (g) → CO2 (g) + 2H2O (g)
Consider the following reaction between hydrogen sulfide (H2S) gas and oxygen (O2) gas. 2 H2S(g) + 3 O2(g) → 2 H2O(g) + 2 SO2(g) Using standard enthalpies of formation, calculate the standard enthalpy change for this reaction. _____ kJ/mol Is this reaction endothermic or exothermic? a. endothermic b. exothermic
For the following reaction 2H2S (g) + 3O2 (g) → 2H2O (l) + 2SO2 (g) Calculate ΔH° from the given data. Is the reaction exothermic or endothermic? ΔH°f (H2S) = -20.15 kJ/mol; ΔH°f (O2) = 0 kJ/, mol; ΔH°f (H2O) = -285.8 kJ/mol; ΔH°f (SO2) = -296.4 kJ/mol
Enthalpy H is a measure of the energy content of a system at constant pressure. Chemical reactions involve changes in enthalpy, ΔH, which can be measured and calculated: ΔH°rxn = Ʃproducts mΔH°f - Ʃreactants nΔH°f where the subscript "rxn" is for "enthalpy of reaction" and "f" is for "enthalpy of formation" and m and n represent the appropriate stoichiometric coefficients for each substance. The following table lists some enthalpy of formation values for selected substances. Determine the enthalpy for this reaction: Al(OH)3 (s) + 3HCl (g) → AlCl3 (s) + 3H2O (l) Express your answer in kilojoules per mole to one decimal place. Consider the reaction 2Al(OH)3 (s) → Al2O3 (s) + 3H2O (l) with enthalpy of reaction ΔH°rxn = 21.0 kJ/mol What is the enthalpy of formation of Al 2O3(s)? Express your answer in kilojoules per mole to one decimal place.
What is the change in enthalpy at 25°C and 1 atm for the reaction of 8.00 mol of elemental iron with excess oxygen gas? 4Fe (s) + 3O2 (g) → Fe2O3 (s):        ΔH° = -1651 kJ Select one: a. -1651 kJ b. -3302 kJ c. -826.5 kJ d. -13208 kJ e. -412.8 kJ
Using values from Appendix C in the textbook, calculate the standard enthalpy change for each of the following reactions. 2SO2(g) + O2(g) → 2SO3(g)                              ΔH°rxn =Mg(OH)2(s) → MgO(s) + H2O(l)                         ΔH°rxn =N2O4(g) + 4H2(g) → N2(g) + 4H2O(g)                ΔH°rxn = SiCl4(l) + 2H2O(l) → SiO2(g) + 4HCl(g)              ΔH°rxn =
A scientist measures the standard enthalpy change for the following reaction to be -665.2 kJ: P4O10 (s) + 6H2O (l) → 4H3PO4 (aq) Based on this value and the standard enthalpies of formation for the other substances, the standard enthalpy of formation of H3PO4 (aq) is _________________.
The value of ΔH°rxn for the reaction below is - 1036 kJ: 2H2S (g) + 3O2 (g) → 2SO2 (g) + 2H2O (g) Estimate the average energy of the individual bonds in SO2 from the appropriate average bond energies. 
From the standard enthalpies of formation, calculate ΔHrxn degree for the reaction C6H12 (l) + 9O2 (g) → 6CO2 (g) + H2O (l) 
Methyl tert-butyl ether (MTBE, C 5H12O, a gasoline additive used to boost octane ratings, has ΔH°f = -313.6 kJ/mol. Part AWrite a balanced equation for its combustion reaction C5H12O(l) + 6O2 (g) → 5CO2 (g) + 6H2O(l)C5H12O(l) + 15/2O2 (g) → 5CO2 (g) + 6H2O(l)C5H12O(l) + 15/2O2 (g) → 5H2CO3 (g) + H2O(l)2C5H12O(l) + 5O2 (g) → 2C 5H12O6 (s)Part B Calculate its standard heat of combustion in kilojoules.Express your answer using four significant figures
Using the standard enthalpies of formation, what is the standard enthalpy of reaction? CO(g) + H2O(g) → CO2(g) + H2(g) 
What is the standard enthalpy of formation of CH3CH2CH2CHO(l)? 2CH3CH2CH2CHO (l) + 5O2 (g) → 8H2O (l) + 8CO2 (g):         ΔH° = -4943.6 kJ Substance             ΔH°f (kJ/mol) CO2 (g)                    - 393.5 H2O (l)                     - 285.8 Select one: a. -245.4 kJ/mol b. +245.4 kJ/mol c. -1792.5 kJ/mol d -3151.1 kJ/mol e. +3151.1 kJ/mol
Using the standard enthalpies of formation, what is the standard enthalpy of reaction? CO (g) + H2O (g) → CO2 (g) + H2 (g)
Calculate the standard enthalpy change for the following reaction at 25 °C. Standard enthalpy of formation values can be found in this table. HCl(g) + NaOH(s) → NaCl(s) + H 2O(l)
Using standard heats of formation, calculate the standard enthalpy change for the following reaction. N2 (g) + 3H2 (g) → 2NH3 (g) 
What is  ΔH° for the following reaction? 2CH3OH (l) + 3O2 (g) → 2CO2 (g) + 4H2O (l) Substance                 ΔH°f (kJ/mol) CH3OH (l)                    - 238.7 CO2 (g)                        - 393.5 H2O (l)                         - 285.8 Select one: a. +1692.2 kJ b. -452.6 kJ c. -1452.2 kJ d. + 2599.0 kJ e. -2599.0 kJ
Use the average bond energies listed in the textbook to estimate how much more energy is released by the reaction C (s) + O2 (g) → CO2 (g) than by the reaction C (s) + 1/2O2 (g) → CO (g) Do not use mathematical signs in your answer.
Using standard heats of formation, calculate the standard enthalpy change for the following reaction. 2H2O (l) → 2H2 (g) + O2 (g)
Consider the following balanced reaction: 2A2 + B → C + 2D What is the enthalpy of reaction if the enthalpy of formation of the compounds is given as A2 = 19.03  kJ/mol; B = 5.6 kJ/mol; C = 10.21 kJ/mol; D = 11.1 kj/mol. Record your answer in scientific notation using 3 significant figures.
Consider the following generic reaction: 2A + 3B → C       ΔHrxn = -125 kJ Determine the amount of heat emitted when each of the following completely reacts (assume that there is more than enough of the other reactant)Part A2 mol APart B3 mol B
Calculate the standard enthalpy change for the following reaction at 25°C. Standard enthalpy of forma values can be found in this table. MgCl2(s) + H2O(l) → MgO(s) + 2HCl(g)
Data: ΔHf values: CH4 (g), -74.8 kJ: CO2 (g), -393.5 kJ: H2O (l), -285.8 kJ. Using the ΔHf data above, calculate ΔHrxn for the reaction below. Reaction: CH4 (g) + 2O2 (g) → CO2 (g) + 2H2O (l) a. -604.2 kJ b. 8.90.3 kJ c. -997.7 kJ d. -890.3 kJ e. none of the above
Calculate ΔH°f  (in kilojoules per mole) for benzene. C6H6, from the following data: 2C6H6(l) + 15O2(g) → 12CO2 (g) + 6H2O(l),      ΔH° = -6543.0 kJCO2 (g),                                                             ΔH°      f = -393.5 kJ/molH2O(l),                                                               ΔH°      f = -285.8 kJ/molExpress the enthalpy change in kilojoules per mole to three significant digits. 
What is the heat of combustion of ethane, C 2H6, in kilojoules per mole of ethane? 
Be sure to answer all parts.Calculate the heats of combustion for the following reactions. Use the standard enthalpies of formation. (a) C2H4 (g) + 3O2 (g) → 2CO (g) + 2H2O (l) kJ/mol (b) 2H2S (g) + 3O2 (g) → 2H2O (l) + 2SO2 (g) kJ/mol
Using standard heats of formation, calculate the standard enthalpy change for the following reaction. 2BrF3 (g) → Br2 (g) + 3F2 (g)
When one mole of gasecus ethanol, C2H5OH, reacts with three moles of gaseous oxygen, two moles of gaseous carbon diaxide and three moles of water vapor are produced. What is the thermochemical equation for the reaction? a. C2H5OH (g) + 3O2 (g) → 2CO2 (g) + 3H2O (g) ΔH = -1277.1 kJb. C2H5OH (g) + 3O2 (g) → 2CO2 (g) + 3H2O (g) ΔH = +400.0 kJc. C2H5OH (g) + 3O2 (g) → 2CO2 (g) + 3H2O (g) ΔH = +1277.1 kJd. C2H5OH (g) + 3O2 (g) → 2CO2 (g) + 3H2O (g) ΔH = -1747.7 kJe. None of these
Calculate the standard enthalpy change for the following reaction at 25°C. Standard enthalpy of formation can found in this table. HCl (g) + NaOH (s) → NaCl (s) + H 2O (l)
Use the following data to calculate the standard heat (enthalpy) of formation, ΔH °f, of manganese(IV) oxide, MnO2 (s). 2MnO2 (s) → 2MnO (s) + O2 (g)          ΔH = 264 kJ MnO2 (s) + Mn(s) → 2MnO (s)           ΔH = -240 kJ Select one:(a) -504 kJ (b) -372 kJ (c) 24 kJ (d) -24 kJ (e) 504 kJ
Part AThe value of ΔH° for the following reaction is -3351 kJ: 2Al (s) + 3O2 (g) → 2Al2O3 (s) The value of ΔH°f for Al2O3 (s) is _____ kJ. (a) -16.43 (b) -1676 (c) -3351 (d) +3351 (e) -32.86
Be sure to answer all parts.Stearic acid (C18H36O2) is a typical fatty acid, a molecule with a long hydrocarbon chain and an organic acid group (COOH) at the end. It is used to make cosmetics, ointments, soaps, and candles and is found in animal tissue as part of many saturated fats. In fact, when you eat meat, chances are that you are ingesting some fats that contain stearic acid. Calculate the heat (q) in kJ and kcal when 39.8 g of stearic acid is burned completely given that ΔH°f = -948 kJ/mol. kJ kcal
When solutions containing silver ions and chloride ions are mixed, silver chloride precipitates: Ag+ (ag) + Cl - (aq) → AgCI(s)       Δ H = -65.5 kJ Calculate ΔH for formation of 0.430 mol of AgCl by this reaction.  Calculate ΔH for the formation of 6.00 g of AgCl.Calculate ΔH when 9.23 x 10-4 mol of AgCI dissolves in water.
Sulfur dioxide, SO2(g), can react with oxygen to produce sulfur trioxide, SO3(g), by the following reaction 2SO2(g) + O2(g) → 2SO3(g) The standard enthalpies of formation for SO2(g) and SO3(g) are ΔH°f[SO2(g)] = 296.8 kJ/mol ΔH°f[SO3(g)] = -395.7 kJ/mol Calculate the amount of energy in the form of heat that is produced when a volume of 3.24 L of SO2(g) is converted to 3.24 L of SO3(g) according to this process at a constant pressure and temperature of 1.00 atm and 25.0°C. Assume ideal gas behavior.
Be sure to answer all parts.Three of the reactions that occur when the paraffin of a candle (typical formula C 21H44) burns are as follows: (1) Complete combustion forms CO2 and water vapor. (2) Incomplete combustion forms CO and water vapor. (3) Some wax is oxidized to elemental C (soot) and water vapor. Part 1 out of 3(a) Find ΔH°combustion of each reaction for 1 mol of C21H44 (ΔH°f of C21H44 = -476 kJ/mol: use graphite for elemental carbon). 
The explosive nitroglycerin (C3H5N3O9) decomposes rapidly upon ignition or sudden impact according to the following balanced equation:4 C3H5N3O9 (l) →12 CO2 (g) +10 H2O (g) + 6 N2 (g) + O2 (g)       ΔHorxn = −5678 kJCalculate the standard enthalpy of formation (ΔHof) for nitroglycerin.