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

Thermochemical Equations

General Chemistry

8. Thermochemistry

Thermochemical Equations

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Multiple Choice

Use the standard reaction enthalpies given below to determine ΔH°rxn for the following reaction: 4 NO(g) + 2 O2(g) → 4 NO2(g). Given: N2(g) + O2(g) → 2 NO(g), ΔH°rxn = +183 kJ. What is the ΔH°rxn for the reaction 4 NO(g) + 2 O2(g) → 4 NO2(g)?

-366 kJ

+114 kJ

-114 kJ

+366 kJ

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Verified step by step guidance

Understand that the problem involves using Hess's Law, which states that the total enthalpy change for a reaction is the sum of the enthalpy changes for each step of the reaction.

Identify the given reaction and the target reaction. The given reaction is: \( \text{N}_2(g) + \text{O}_2(g) \rightarrow 2 \text{NO}(g) \) with \( \Delta H^\circ_{rxn} = +183 \text{kJ} \). The target reaction is: \( 4 \text{NO}(g) + 2 \text{O}_2(g) \rightarrow 4 \text{NO}_2(g) \).

Recognize that the target reaction can be achieved by manipulating the given reaction. Specifically, you need to double the given reaction to match the stoichiometry of the target reaction: \( 2 \times (\text{N}_2(g) + \text{O}_2(g) \rightarrow 2 \text{NO}(g)) \). This results in \( 2 \text{N}_2(g) + 2 \text{O}_2(g) \rightarrow 4 \text{NO}(g) \) with \( \Delta H^\circ = 2 \times 183 \text{kJ} \).

Consider the enthalpy change for the formation of \( \text{NO}_2 \) from \( \text{NO} \) and \( \text{O}_2 \). The reaction \( 4 \text{NO}(g) + 2 \text{O}_2(g) \rightarrow 4 \text{NO}_2(g) \) can be seen as the reverse of the formation of \( \text{NO} \) from \( \text{N}_2 \) and \( \text{O}_2 \).

Apply Hess's Law to find the enthalpy change for the target reaction by summing the enthalpy changes of the steps involved. Since the target reaction is the reverse of the doubled given reaction, the enthalpy change will be the negative of the doubled enthalpy change: \( \Delta H^\circ_{rxn} = -2 \times 183 \text{kJ} \).