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
Sections
Nature of Energy
Kinetic & Potential Energy
First Law of Thermodynamics
Internal Energy
Endothermic & Exothermic Reactions
Heat Capacity
Constant-Pressure Calorimetry
Constant-Volume Calorimetry
Thermal Equilibrium
Thermochemical Equations
Formation Equations
Enthalpy of Formation
Hess's Law
Additional Guides
Enthalpy
LearnAdditional Practice
Next SectionEnthalpy of Formation

Formation Equations involve the standard states of elements combining to form 1 mole of product.

Standard States & Formation Equations

Concept #1: The Natural State (Standard State)

Example #1: Which of the following elements is found in its standard state?

Example #2: Write the formation equation for methanethiol, CH3SH. 

Practice: Which of the following represents the formation equation for barium nitrate, Ba(NO3)2?

Practice: Identify a substance that is not in its standard state.

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. 

Previous SectionThermochemical Equations
Next SectionEnthalpy of Formation
Additional Problems
Which of the following has a non-zero ΔHf°?   a. O2 (l) b. C (graphite) c. N2 (g) d. F2 (g) e. Cl2 (g)
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
ΔHf° is not zero for which one of the following: O­2(g) C (graphite) F2(s) H2(g) Br­2(l)  
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)
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)
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.    
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)
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.  
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)
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)
Determine the answer for the question below.
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)
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
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)
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
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)
 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)
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)
Which of the following substances have a standard heat of formation (ΔHf°) of zero?a) Cl2(g) at 2 atmb) C2H6 at standard conditionsc) O2(g) at 25.0 °Cd) 1 atm Fe at 1200 °C