# Enthalpy Changes and Calorimetry

*Time: 20 min. 6 questions.*

## Instructions

Answer all six questions. For multiple choice questions, select the best answer. For short answer questions, write a complete explanation. For the true or false question, state whether the claim is true or false and briefly justify your answer. For the numeric question, show your calculation and include units. You may use a calculator.

## Questions

1. A student burns 2.5 g of ethanol in a bomb calorimeter. The temperature of 1000 g of water surrounding the bomb rises by 8.2°C. 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) 8.6 kJ
B) 34.2 kJ
C) 86 kJ
D) 342 kJ

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

2. A chemical reaction absorbs 45 kJ of energy from the surroundings. Write the ΔH value for this reaction and explain what the sign tells you about whether the reaction is endothermic or exothermic. ([Outcome](https://goa-cc-uat-aili-app-001.azurewebsites.net/explore/node/23638))

3. True or false: In an exothermic reaction, the enthalpy of the products is greater than the enthalpy of the reactants. ([Outcome](https://goa-cc-uat-aili-app-001.azurewebsites.net/explore/node/23643))

4. The combustion of methane is written as CH₄(g) + 2O₂(g) → CO₂(g) + 2H₂O(l), ΔH = −890 kJ/mol. What does the negative sign indicate, and why is this reaction important for energy use in society? ([Outcome](https://goa-cc-uat-aili-app-001.azurewebsites.net/explore/node/23638), [Outcome](https://goa-cc-uat-aili-app-001.azurewebsites.net/explore/node/23643))

5. A student collects the following calorimetry data: mass of water = 500 g, initial temperature = 20.0°C, final temperature = 24.5°C, specific heat capacity of water = 4.18 J/g°C. Calculate the heat absorbed by the water in kilojoules. ([Outcome](https://goa-cc-uat-aili-app-001.azurewebsites.net/explore/node/23634), [Outcome](https://goa-cc-uat-aili-app-001.azurewebsites.net/explore/node/23641))

6. An energy diagram shows that reactants are at 150 kJ, products are at 80 kJ, and the activation energy is 60 kJ. Is this reaction endothermic or exothermic, and what is the enthalpy change? ([Outcome](https://goa-cc-uat-aili-app-001.azurewebsites.net/explore/node/23653))

## Curriculum Coverage

| Question | Outcome Alias | Specific Outcome |
|---|---|---|
| 1 | [Outcome](https://goa-cc-uat-aili-app-001.azurewebsites.net/explore/node/23634) | Recall the application of Q = mcΔt to the analysis of heat transfer |
| 2 | [Outcome](https://goa-cc-uat-aili-app-001.azurewebsites.net/explore/node/23638) | Use and interpret ΔH notation to communicate and calculate energy changes |
| 3 | [Outcome](https://goa-cc-uat-aili-app-001.azurewebsites.net/explore/node/23643) | Classify chemical reactions as endothermic or exothermic |
| 4 | [Outcome](https://goa-cc-uat-aili-app-001.azurewebsites.net/explore/node/23638), [Outcome](https://goa-cc-uat-aili-app-001.azurewebsites.net/explore/node/23643) | Use ΔH notation and classify reactions as endothermic or exothermic |
| 5 | [Outcome](https://goa-cc-uat-aili-app-001.azurewebsites.net/explore/node/23634), [Outcome](https://goa-cc-uat-aili-app-001.azurewebsites.net/explore/node/23641) | Apply Q = mcΔt and use calorimetry data to determine enthalpy changes |
| 6 | [Outcome](https://goa-cc-uat-aili-app-001.azurewebsites.net/explore/node/23653) | Analyze and label energy diagrams of a chemical reaction |

## Answer Key

1. **Answer: B) 34.2 kJ**
 Using Q = mcΔt: Q = 1000 g × 4.18 J/g°C × 8.2°C = 34,276 J ≈ 34.2 kJ, which is the heat released by the combustion of 2.5 g of ethanol.

2. **Answer: ΔH = +45 kJ. The positive sign indicates the reaction is endothermic because energy is absorbed from the surroundings.** ([Outcome](https://goa-cc-uat-aili-app-001.azurewebsites.net/explore/node/23638))

3. **Answer: False.** In an exothermic reaction, the enthalpy of the products is lower than the enthalpy of the reactants, which is why energy is released ([Outcome](https://goa-cc-uat-aili-app-001.azurewebsites.net/explore/node/23643)).

4. **Answer: The negative sign indicates the reaction is exothermic and releases 890 kJ of energy per mole of methane burned.** This reaction is important because combustion of methane (natural gas) is a major energy source for heating, electricity generation, and industrial processes in society ([Outcome](https://goa-cc-uat-aili-app-001.azurewebsites.net/explore/node/23638), [Outcome](https://goa-cc-uat-aili-app-001.azurewebsites.net/explore/node/23643)).

5. **Answer: 9.41 kJ**
 Q = mcΔt = 500 g × 4.18 J/g°C × (24.5 − 20.0)°C = 500 × 4.18 × 4.5 = 9405 J ≈ 9.41 kJ ([Outcome](https://goa-cc-uat-aili-app-001.azurewebsites.net/explore/node/23634), [Outcome](https://goa-cc-uat-aili-app-001.azurewebsites.net/explore/node/23641)).

6. **Answer: The reaction is exothermic. ΔH = −70 kJ.**
 The products (80 kJ) are lower in energy than the reactants (150 kJ), so the reaction releases energy; ΔH = 80 − 150 = −70 kJ ([Outcome](https://goa-cc-uat-aili-app-001.azurewebsites.net/explore/node/23653)).

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*AILI quiz · language en · model claude-haiku-4-5-20251001 · generated 2026-09-17 · id f6ebb046-ff7e-4740-8185-b96b0858efc6*

### 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/23638)
- node:n6: Specific Outcomes for Knowledge (https://goa-cc-uat-aili-app-001.azurewebsites.net/explore/node/23639)
- node:n7: Specific Outcomes for Knowledge (https://goa-cc-uat-aili-app-001.azurewebsites.net/explore/node/23640)
- node:n8: Specific Outcomes for Knowledge (https://goa-cc-uat-aili-app-001.azurewebsites.net/explore/node/23641)
- node:n9: Specific Outcomes for Knowledge (https://goa-cc-uat-aili-app-001.azurewebsites.net/explore/node/23643)
- node:n10: General Outcome 2 (https://goa-cc-uat-aili-app-001.azurewebsites.net/explore/node/23650)
- node:n11: Specific Outcomes for Knowledge (https://goa-cc-uat-aili-app-001.azurewebsites.net/explore/node/23653)