In a constant-volume calorimetry experiment using a bomb calorimeter, what thermodynamic quantity is directly measured?

• A. ΔG (Gibbs free energy change)
• B. ΔE (internal energy change)
• C. ΔS (entropy change)
• D. ΔH (enthalpy change)

Answer: (B)

Verified step by step guidance

1. Understand the function of a bomb calorimeter: It is designed to measure the heat of combustion of a sample at constant volume, which is crucial for determining the internal energy change.
2. Recognize that in a constant-volume process, the work done by the system is zero because the volume does not change. Therefore, the change in internal energy (ΔE) is equal to the heat exchanged (q).
3. Recall the first law of thermodynamics, which states that the change in internal energy (ΔE) is equal to the heat added to the system minus the work done by the system: $\mathrm{\Delta E}=q-w$. In a bomb calorimeter, $w$ is zero, so $\mathrm{\Delta E}=q$.
4. Differentiate between the thermodynamic quantities: ΔH (enthalpy change) is measured at constant pressure, not constant volume. ΔS (entropy change) and ΔG (Gibbs free energy change) are not directly measured in a bomb calorimeter.
5. Conclude that the bomb calorimeter directly measures the internal energy change (ΔE) of the system, as it captures the heat exchanged at constant volume.