# Enthalpy Changes and Calorimetry

*Time: 25 min. 6 questions.*

## Instructions

Answer all six questions. For multiple choice, select the best answer. For short answer, write a complete sentence or brief explanation. For the true or false question, state whether the statement is true or false and give a one-sentence reason. For the numeric question, show your calculation and include units in your final answer.

## Questions

1. Which of the following statements best describes the relationship between enthalpy and molar enthalpy?
A) Enthalpy is the total energy of a system; molar enthalpy is the enthalpy change per mole of a specified substance in the reaction.
B) Enthalpy and molar enthalpy are identical terms used interchangeably in thermochemistry.
C) Enthalpy is measured in joules; molar enthalpy is measured only in calories.
D) Enthalpy applies only to exothermic reactions, while molar enthalpy applies to endothermic reactions.
([Outcome](https://goa-cc-uat-aili-app-001.azurewebsites.net/explore/node/23636))

2. Consider the following balanced thermochemical equation: 2H₂(g) + O₂(g) → 2H₂O(l) ΔH = −572 kJ. Explain what the negative sign in this ΔH value tells you about the reaction. ([Outcome](https://goa-cc-uat-aili-app-001.azurewebsites.net/explore/node/23637))

3. True or false: A negative ΔH value indicates that a reaction is endothermic and absorbs energy from the surroundings. ([Outcome](https://goa-cc-uat-aili-app-001.azurewebsites.net/explore/node/23638))

4. Which process is classified as exothermic?
A) Photosynthesis
B) Melting ice at 0°C
C) Cellular respiration
D) Evaporation of water
([Outcome](https://goa-cc-uat-aili-app-001.azurewebsites.net/explore/node/23643))

5. In a calorimetry experiment, a student burns 1.0 g of a hydrocarbon fuel and observes that the temperature of 1000 g of water increases by 6.5°C. Using Q = mcΔt with a specific heat capacity of 4.18 J/(g·°C), calculate the heat released by the fuel in kilojoules. ([Outcome](https://goa-cc-uat-aili-app-001.azurewebsites.net/explore/node/23641))

6. A student performs a calorimetry experiment where 50 g of hot water at 80°C is mixed with 50 g of cold water at 20°C in an insulated container. Using Q = mcΔt with a specific heat capacity of 4.18 J/(g·°C), determine the final equilibrium temperature of the mixture. ([Outcome](https://goa-cc-uat-aili-app-001.azurewebsites.net/explore/node/23634))

## Curriculum Coverage

| Question | Outcome Alias | Outcome Description |
|---|---|---|
| 1 | [Outcome](https://goa-cc-uat-aili-app-001.azurewebsites.net/explore/node/23636) | Define enthalpy and molar enthalpy for chemical reactions |
| 2 | [Outcome](https://goa-cc-uat-aili-app-001.azurewebsites.net/explore/node/23637) | Write balanced equations for chemical reactions that include energy changes |
| 3 | [Outcome](https://goa-cc-uat-aili-app-001.azurewebsites.net/explore/node/23638) | Use and interpret ΔH notation to communicate and calculate energy changes |
| 4 | [Outcome](https://goa-cc-uat-aili-app-001.azurewebsites.net/explore/node/23643) | Classify chemical reactions as endothermic or exothermic |
| 5 | [Outcome](https://goa-cc-uat-aili-app-001.azurewebsites.net/explore/node/23641) | Use calorimetry data to determine the enthalpy changes in chemical reactions |
| 6 | [Outcome](https://goa-cc-uat-aili-app-001.azurewebsites.net/explore/node/23634) | Apply Q = mcΔt to the analysis of heat transfer |

## Answer Key

1. **A**, Molar enthalpy is the enthalpy change expressed per mole of a specified reactant or product, whereas enthalpy is the total energy content; this distinction is central to the definition ([Outcome](https://goa-cc-uat-aili-app-001.azurewebsites.net/explore/node/23636)).

2. **The negative sign indicates that the reaction is exothermic and releases 572 kJ of energy to the surroundings for every 2 moles of hydrogen gas that react.** The ΔH notation communicates both the magnitude and direction of energy change in the reaction ([Outcome](https://goa-cc-uat-aili-app-001.azurewebsites.net/explore/node/23637)).

3. **False**, A negative ΔH indicates an exothermic reaction that releases energy to the surroundings; an endothermic reaction has a positive ΔH and absorbs energy ([Outcome](https://goa-cc-uat-aili-app-001.azurewebsites.net/explore/node/23638)).

4. **C**, Cellular respiration is exothermic because it releases energy from the breakdown of glucose and other organic molecules; photosynthesis and evaporation are endothermic, and melting ice requires heat input ([Outcome](https://goa-cc-uat-aili-app-001.azurewebsites.net/explore/node/23643)).

5. **27.2 kJ**, Using Q = mcΔt: Q = 1000 g × 4.18 J/(g·°C) × 6.5°C = 27,170 J; converting to kilojoules: 27,170 J ÷ 1000 = 27.2 kJ ([Outcome](https://goa-cc-uat-aili-app-001.azurewebsites.net/explore/node/23641)).

6. **50°C**, Heat lost by hot water equals heat gained by cold water; 50 g × 4.18 J/(g·°C) × (80 − T) = 50 g × 4.18 J/(g·°C) × (T − 20), which simplifies to 80 − T = T − 20, giving T = 50°C ([Outcome](https://goa-cc-uat-aili-app-001.azurewebsites.net/explore/node/23634)).

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*AILI quiz · language en · model claude-haiku-4-5-20251001 · generated 2026-09-17 · id 056a4e0a-87b7-4417-b941-27bbc2117528*

### 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)
- node:n11: General Outcome 2 (https://goa-cc-uat-aili-app-001.azurewebsites.net/explore/node/23650)
- node:n12: Specific Outcomes for Knowledge (https://goa-cc-uat-aili-app-001.azurewebsites.net/explore/node/23652)
- node:n13: Specific Outcomes for Knowledge (https://goa-cc-uat-aili-app-001.azurewebsites.net/explore/node/23653)