# Enthalpy Changes and Calorimetry

*Time: 25 min. 6 questions.*

## Instructions

Answer all six questions. For multiple-choice questions, select the best answer. For short-answer and true/false questions, show your reasoning or state whether the statement is correct and why. For numeric questions, include units in your final answer and show your calculation. You may use a calculator.

## Questions

1. A student burns 2.0 g of ethanol in a bomb calorimeter and observes a temperature increase of 8.5°C in 1000 g of water surrounding the calorimeter. Using Q = mcΔt, what is the heat released by the combustion? (Assume the specific heat capacity of water is 4.18 J/g°C.)

A) 35.53 kJ
B) 3.553 kJ
C) 35530 J
D) 0.035 kJ

([Outcome](https://goa-cc-uat-aili-app-001.azurewebsites.net/explore/node/23634))

2. Which of the following statements about enthalpy is true?

A) Enthalpy is the total kinetic energy of all particles in a system.
B) Enthalpy is a measure of the heat content of a substance at constant pressure.
C) Enthalpy can only be measured in units of joules per second.
D) Enthalpy is always positive for all chemical reactions.

([Outcome](https://goa-cc-uat-aili-app-001.azurewebsites.net/explore/node/23636))

3. The combustion of methane is represented by the equation CH₄(g) + 2O₂(g) → CO₂(g) + 2H₂O(l), ΔH = −890 kJ/mol. Is this reaction endothermic or exothermic, and what does the numerical value tell you?

([Outcome](https://goa-cc-uat-aili-app-001.azurewebsites.net/explore/node/23643))

4. True or False: The ΔH notation in a thermochemical equation refers to the enthalpy change per mole of the reaction as written.

([Outcome](https://goa-cc-uat-aili-app-001.azurewebsites.net/explore/node/23638))

5. A student uses calorimetry to determine the enthalpy change of a neutralization reaction. The student measures the temperature change of the solution, the mass of the solution, and uses Q = mcΔt to calculate the heat absorbed or released. What is the relationship between the heat measured in the calorimeter (q) and the enthalpy change (ΔH) for this reaction?

([Outcome](https://goa-cc-uat-aili-app-001.azurewebsites.net/explore/node/23641))

6. Calculate the standard enthalpy change for the reaction 2C(s) + O₂(g) → 2CO(g) using the following standard enthalpies of formation: ΔH°f[C(s)] = 0 kJ/mol, ΔH°f[O₂(g)] = 0 kJ/mol, ΔH°f[CO(g)] = −110.5 kJ/mol. Show your work.

([Outcome](https://goa-cc-uat-aili-app-001.azurewebsites.net/explore/node/23639))

## Curriculum Coverage

| Question | Outcome Alias | Specific Outcome Code |
|---|---|---|
| 1 | [Outcome](https://goa-cc-uat-aili-app-001.azurewebsites.net/explore/node/23634) | 30-A1.1k |
| 2 | [Outcome](https://goa-cc-uat-aili-app-001.azurewebsites.net/explore/node/23636) | 30-A1.3k |
| 3 | [Outcome](https://goa-cc-uat-aili-app-001.azurewebsites.net/explore/node/23643) | 30-A1.10k |
| 4 | [Outcome](https://goa-cc-uat-aili-app-001.azurewebsites.net/explore/node/23638) | 30-A1.5k |
| 5 | [Outcome](https://goa-cc-uat-aili-app-001.azurewebsites.net/explore/node/23641) | 30-A1.8k |
| 6 | [Outcome](https://goa-cc-uat-aili-app-001.azurewebsites.net/explore/node/23639) | 30-A1.6k |

## Answer Key

1. **Answer: C) 35530 J** (or 35.53 kJ). Using Q = mcΔt: Q = (1000 g)(4.18 J/g°C)(8.5°C) = 35530 J, which equals the heat released by combustion at constant pressure.

2. **Answer: B) Enthalpy is a measure of the heat content of a substance at constant pressure.** Enthalpy (H) is defined as the total heat content of a system and is the appropriate measure for processes occurring at constant pressure, such as most laboratory reactions.

3. **Answer: This reaction is exothermic. The negative value of ΔH = −890 kJ/mol indicates that 890 kilojoules of energy are released per mole of methane burned.** A negative ΔH always signals an exothermic reaction.

4. **Answer: True.** The ΔH value in a thermochemical equation represents the enthalpy change for the reaction as written, per mole of reaction as specified by the stoichiometric coefficients.

5. **Answer: For a reaction at constant pressure, the heat measured by the calorimeter (q) equals the enthalpy change of the reaction (ΔH = q).** Calorimetry directly measures the heat transfer, which equals ΔH when the reaction occurs at constant atmospheric pressure.

6. **Answer: ΔH°rxn = −221 kJ/mol.** Using ΔH°rxn = Σ(ΔH°f products) − Σ(ΔH°f reactants): ΔH°rxn = [2(−110.5)] − [2(0) + 1(0)] = −221 kJ/mol; the reaction is exothermic.

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*AILI quiz · language en · model claude-haiku-4-5-20251001 · generated 2026-09-17 · id d48d34de-7267-4ff7-ad87-59aa03a4d4aa*

### Sources

- node:n1: Unit A: Thermochemical Changes (https://goa-cc-uat-aili-app-001.azurewebsites.net/explore/node/23632)
- node:n2: General Outcome 1 (https://goa-cc-uat-aili-app-001.azurewebsites.net/explore/node/23633)
- node:n3: Specific Outcomes for Knowledge (https://goa-cc-uat-aili-app-001.azurewebsites.net/explore/node/23634)
- node:n4: Specific Outcomes for Knowledge (https://goa-cc-uat-aili-app-001.azurewebsites.net/explore/node/23636)
- node:n5: Specific Outcomes for Knowledge (https://goa-cc-uat-aili-app-001.azurewebsites.net/explore/node/23637)
- node:n6: Specific Outcomes for Knowledge (https://goa-cc-uat-aili-app-001.azurewebsites.net/explore/node/23638)
- node:n7: Specific Outcomes for Knowledge (https://goa-cc-uat-aili-app-001.azurewebsites.net/explore/node/23639)
- node:n8: Specific Outcomes for Knowledge (https://goa-cc-uat-aili-app-001.azurewebsites.net/explore/node/23640)
- node:n9: Specific Outcomes for Knowledge (https://goa-cc-uat-aili-app-001.azurewebsites.net/explore/node/23641)
- node:n10: Specific Outcomes for Knowledge (https://goa-cc-uat-aili-app-001.azurewebsites.net/explore/node/23643)