Does a measurement carried out in a bomb calorimeter give a value for ∆H or ∆E? Explain.

Verified step by step guidance

1. Understand the terms: ∆H represents the change in enthalpy, which is the heat absorbed or released at constant pressure. ∆E represents the change in internal energy, which is the total energy change in a system.
2. Recognize the setup of a bomb calorimeter: It is designed to measure changes in a closed system at constant volume. This setup is crucial for determining which thermodynamic quantity is measured.
3. Connect the setup to the thermodynamic concept: Since the bomb calorimeter operates at constant volume, the work done by the system (W) is zero. Recall the first law of thermodynamics, ∆E = q + W, where q is heat and W is work.
4. Apply the first law of thermodynamics: In the context of a bomb calorimeter, since W = 0 (no work done at constant volume), the equation simplifies to ∆E = q_v, where q_v is the heat absorbed or released at constant volume.
5. Conclude the specific measurement: Therefore, a bomb calorimeter measures the change in internal energy (∆E) of the reaction, not the change in enthalpy (∆H).

Key Concepts

Enthalpy (∆H)

Enthalpy (∆H) is a thermodynamic quantity that represents the total heat content of a system at constant pressure. It accounts for the internal energy of the system plus the product of its pressure and volume. In chemical reactions, changes in enthalpy indicate whether a reaction is exothermic (releases heat) or endothermic (absorbs heat).

Internal Energy (∆E)

Internal Energy (∆E) is the total energy contained within a system, including kinetic and potential energies of the particles. It is a state function that reflects the energy changes due to heat transfer and work done on or by the system. The relationship between internal energy and enthalpy is crucial in understanding energy changes during chemical reactions.

Bomb Calorimeter

A bomb calorimeter is a device used to measure the heat of combustion of a substance at constant volume. It provides a direct measurement of the change in internal energy (∆E) during a reaction, as the volume remains constant and no work is done by expansion. However, since most chemical reactions occur at constant pressure, the results can be converted to enthalpy changes, but the initial measurement reflects ∆E.