Which statement best describes how a constant-pressure calorimeter works?

• A. It isolates the reaction from the surroundings to prevent any heat exchange.
• B. It determines the heat change by keeping the volume constant and measuring pressure changes.
• C. It measures the heat change of a reaction by monitoring the temperature change of a solution at constant atmospheric pressure.
• D. It uses electrical energy to directly calculate the enthalpy change of a reaction.

Answer: (C)

Verified step by step guidance

1. Understand that a constant-pressure calorimeter is designed to measure heat changes during a reaction occurring at constant atmospheric pressure.
2. Recognize that in such a calorimeter, the volume can change, but the pressure remains constant, which is typical for reactions open to the atmosphere.
3. Know that the calorimeter contains a solution whose temperature change is monitored as the reaction proceeds.
4. Use the temperature change of the solution along with its known heat capacity to calculate the heat absorbed or released by the reaction.
5. Recall that this heat change corresponds to the enthalpy change (\$\Delta H\$) of the reaction because the process occurs at constant pressure.