Table of contents

1. Intro to General Chemistry3h 48m
2. Atoms & Elements4h 16m
3. Chemical Reactions4h 10m
4. BONUS: Lab Techniques and Procedures1h 38m
5. BONUS: Mathematical Operations and Functions48m
6. Chemical Quantities & Aqueous Reactions3h 53m
7. Gases3h 49m
8. Thermochemistry2h 37m
9. Quantum Mechanics2h 58m
10. Periodic Properties of the Elements3h 9m
11. Bonding & Molecular Structure3h 29m
12. Molecular Shapes & Valence Bond Theory1h 57m
13. Liquids, Solids & Intermolecular Forces2h 23m
14. Solutions3h 1m
15. Chemical Kinetics2h 53m
16. Chemical Equilibrium2h 29m
17. Acid and Base Equilibrium5h 1m
18. Aqueous Equilibrium4h 47m
19. Chemical Thermodynamics1h 50m
20. Electrochemistry2h 42m
21. Nuclear Chemistry2h 36m
22. Organic Chemistry5h 7m
23. Chemistry of the Nonmetals2h 39m
24. Transition Metals and Coordination Compounds3h 16m

8. Thermochemistry

Enthalpy of Formation

General Chemistry

8. Thermochemistry

Enthalpy of Formation

Previous problemNext problem

Struggling with General Chemistry?

Join thousands of students who trust us to help them ace their exams!Watch the first video

Multiple Choice

Use standard enthalpies of formation to calculate ΔHºrxn for the following reaction: 2H2S(g) + 3O2(g) → 2H2O(l) + 2SO2(g). Which of the following is the correct value for ΔHºrxn?

-640 kJ/mol

-890 kJ/mol

-1120 kJ/mol

-450 kJ/mol

Previous problemNext problem

Verified step by step guidance

Identify the standard enthalpy of formation (ΔHºf) for each compound involved in the reaction. These values are typically found in tables in chemistry textbooks or reliable databases. For this reaction, you need the ΔHºf for H2S(g), O2(g), H2O(l), and SO2(g). Note that the ΔHºf for elements in their standard state, like O2(g), is zero.

Write the balanced chemical equation for the reaction: 2H2S(g) + 3O2(g) → 2H2O(l) + 2SO2(g). Ensure that the equation is balanced with respect to both mass and charge.

Apply the formula for calculating the standard enthalpy change of the reaction (ΔHºrxn) using the standard enthalpies of formation: ΔHºrxn = Σ(ΔHºf of products) - Σ(ΔHºf of reactants).

Substitute the ΔHºf values into the formula. Multiply the ΔHºf of each compound by its stoichiometric coefficient from the balanced equation. For example, for H2O(l), you would calculate 2 * ΔHºf(H2O(l)).

Calculate the sum of the enthalpies for the products and the reactants separately, then subtract the sum of the reactants from the sum of the products to find ΔHºrxn. This will give you the standard enthalpy change for the reaction.