Question

The Joule-Thomson expansion of a gas is:

• A. Isentropic
• B. Isenthalpic
• C. Isobaric
• D. Isochoric

Hint:

For the Joule-Thomson expansion, remember that the enthalpy remains constant. This is key to understanding the behavior of the gas during the expansion process.

Answer 1

The Correct Option is B

The Joule-Thomson expansion of a gas is a thermodynamic process where the gas expands through a porous plug or valve, and no heat exchange occurs with the surroundings. During this expansion, the enthalpy of the gas remains constant. Here’s a breakdown of the process:

Step 1: Definition of the Joule-Thomson process.
The Joule-Thomson effect refers to the change in temperature of a real gas when it undergoes an expansion or compression at constant enthalpy. It is an irreversible process where there is no exchange of heat with the surroundings, i.e., it is an adiabatic process, but the key feature is that the enthalpy remains constant.

Step 2: Understanding isenthalpic processes.
An isenthalpic process is one where the enthalpy remains constant. Since the Joule-Thomson expansion occurs at constant enthalpy, it is classified as an isenthalpic process. Therefore, the correct answer is (B).

Step 3: Excluding other options.
Option (A) Isentropic: An isentropic process means both entropy and energy remain constant. Since the Joule-Thomson expansion does not conserve entropy, it is not an isentropic process.
Option (C) Isobaric: In an isobaric process, the pressure remains constant. The pressure in a Joule-Thomson expansion may change as the gas expands, so this option is incorrect.
Option (D) Isochoric: An isochoric process occurs at constant volume. The Joule-Thomson expansion involves changes in volume, making this option incorrect.