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

What is the standard enthalpy change of formation for NaCl(aq) at 25°C?

-411 kJ/mol

-425 kJ/mol

-418 kJ/mol

-407 kJ/mol

Previous problemNext problem

Verified step by step guidance

Understand that the standard enthalpy change of formation (ΔH_f°) is the change in enthalpy when one mole of a compound is formed from its elements in their standard states at 25°C and 1 atm.

Write the balanced chemical equation for the formation of NaCl(aq) from its elements in their standard states: Na(s) + 1/2 Cl2(g) → NaCl(aq).

Use Hess's Law, which states that the total enthalpy change for a reaction is the same, no matter how many steps the reaction is carried out in, to find the ΔH_f° for NaCl(aq).

Look up the standard enthalpy changes of formation for the reactants and products involved in the reaction. For Na(s) and Cl2(g), these values are typically zero because they are in their standard states.

Calculate the standard enthalpy change of formation for NaCl(aq) by using the formula: ΔH_f° = ΣΔH_f°(products) - ΣΔH_f°(reactants). Substitute the known values into this equation to find the ΔH_f° for NaCl(aq).