---
title: "A student performs an experiment to determine the molar enthalpy of combustion, \\(\\Delta H_{comb}\\), of ethanol, \\(\\text{C}_2\\text{H}_5\\text{OH}(l)\\). A known mass of ethanol is burned in a spirit burner to heat a measured mass of water in an open metal calorimeter. The student assumes that all heat released by the combustion is absorbed by the water and uses \\(q = m c \\Delta T\\) to calculate the experimental molar enthalpy of combustion. However, a portion of the heat released during combustion is transferred to the surrounding air and metal calorimeter cup rather than to the water. Which of the following claims correctly predicts the effect of this heat loss on the calculated magnitude of \\(\\Delta H_{comb}\\) and provides the correct justification?"
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url: "https://nerd-notes.com/ubq/119212/"
date_modified: "2026-08-19T12:39:23+00:00"
---

# A student performs an experiment to determine the molar enthalpy of combustion, \(\Delta H_{comb}\), of ethanol, \(\text{C}_2\text{H}_5\text{OH}(l)\). A known mass of ethanol is burned in a spirit burner to heat a measured mass of water in an open metal calorimeter. The student assumes that all heat released by the combustion is absorbed by the water and uses \(q = m c \Delta T\) to calculate the experimental molar enthalpy of combustion. However, a portion of the heat released during combustion is transferred to the surrounding air and metal calorimeter cup rather than to the water. Which of the following claims correctly predicts the effect of this heat loss on the calculated magnitude of \(\Delta H_{comb}\) and provides the correct justification?

A student performs an experiment to determine the molar enthalpy of combustion, \(\Delta H_{comb}\), of ethanol, \(\text{C}_2\text{H}_5\text{OH}(l)\). A known mass of ethanol is burned in a spirit burner to heat a measured mass of water in an open metal calorimeter. The student assumes that all heat released by the combustion is absorbed by the water and uses \(q = m c \Delta T\) to calculate the experimental molar enthalpy of combustion. However, a portion of the heat released during combustion is transferred to the surrounding air and metal calorimeter cup rather than to the water. Which of the following claims correctly predicts the effect of this heat loss on the calculated magnitude of \(\Delta H_{comb}\) and provides the correct justification?

- **A.** The calculated magnitude of \(\Delta H_{comb}\) is lower than the actual value because the measured \(\Delta T\) of the water is smaller than if all heat were transferred to the water.
- **B.** The calculated magnitude of \(\Delta H_{comb}\) is higher than the actual value because the heat lost to the surroundings increases the measured final temperature of the water.
- **C.** The calculated magnitude of \(\Delta H_{comb}\) is lower than the actual value because the heat loss causes the calculated mass of ethanol burned to be greater than the actual mass consumed.
- **D.** The calculated magnitude of \(\Delta H_{comb}\) is higher than the actual value because the unmeasured heat absorbed by the cup is added directly to the calculated heat absorbed by the water.

*The answer key and step-by-step explanation are available to logged-in users at https://nerd-notes.com/ubq/119212/*