Ch.6 - Thermochemistry WorksheetSee 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

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
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. 
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).
The mechanism for the oxidation of HBr by O2 to form 2 H2 O and Br2 4HBr(g)+O2(g)2H2O(g)+2Br2(g) is shown below. HBr(g)+O2(g)HOOBr(g) HOOBr(g)+HBr(g)2HOBr(g) HOBr(g)+HBr(g)H2O(g)+Br2(g).Calculate the overall standard enthalpy change for the reaction process.
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?
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 (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?
Write an equation for the formation of NH3 (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 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.
Methanol (CH3OH) can be made by the controlled oxidation of methane: CH4(g) + O2(g)  →  CH3OH(g)Use data in Appendix C in the textbook to calculate H H for this reaction.
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
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.
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. 
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 kJWhat 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
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)
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 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.
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
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 ΔH 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:ΔHrxn = products m ΔHf - reactants n ΔHfwhere 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                                 Δ  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 ΔHrxn = 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:
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
Consider the reaction of N2O5 at 25°C for which the following data are relevant:2 N2O5 (g) → 4 NO2 (g) + O2 (g)Substance             ΔH°f                               S°             N 2O5                    11.29 kJ/mol             355.3 J/K mol              NO 2                     33.15 kJ/mol             239.9 J/K mol              O 2                                   ?                     204.8 J/K mol What is ΔH° for the reaction?a) 110.02 kJb) 21.86 kJc) -21.86 kJd) 155.20 kJe) -155.20 kJ
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. -2979KJb. 2979KJc. -703KJd. 703KJ e. -853KJ
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)
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)
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.Choose an enthalpy diagram for the reaction.
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?
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.
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.b) If ΔH°rxn = −1.50 x 104 kJ for the combustion equation, determine ΔH°f of kerosene.c) Calculate the heat released by combustion of 0.50 gal of kerosene ( d of kerosene = 0.749 g/mL).
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.b) If ΔH°rxn = −1.50 x 104 kJ for the combustion equation, determine ΔH°f of kerosene.c) Calculate the heat released by combustion of 0.50 gal of kerosene ( d of kerosene = 0.749 g/mL).d) How many gallons of kerosene must be burned for a kerosene furnace to produce 1250 Btu (1 Btu = 1.055 kJ)?
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?
Methanol (CH3 OH) has been suggested as a fuel to replace gasoline. Write a balanced equation for the combustion of methanol, find ΔH˚rxn, and determine the mass of carbon dioxide emitted per kJ of heat produced. Calculate the same quantity for octane, C8H18. (ΔH˚rxn = –5074.1 kJ/mol for octane.)
Methanol (CH3 OH) has been suggested as a fuel to replace gasoline. Write a balanced equation for the combustion of methanol, find ΔH˚rxn, and determine the mass of carbon dioxide emitted per kJ of heat produced.
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).
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?
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.
Nitric acid, HNO3, can be prepared by the following sequence of reactions:4NH3(g) + 5O2(g) ⟶ 4NO(g) + 6H 2 O(g)2NO(g) + O2(g) ⟶ 2NO2(g)3NO2(g) + H2 O(l) ⟶ 2HNO3(l) + NO(g)How much heat is evolved when 1 mol of NH 3(g) is converted to HNO3(l)? Assume standard states at 25 °C.
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)