Question

The quantity representing change in temperature of a gas with pressure at constant enthalpy is called:

• A. Thermal expansion coefficient
• B. Joule-Thomson coefficient
• C. Compressibility factor
• D. Isothermal pressure

Hint:

Joule–Thomson effect explains cooling of gases in refrigeration and liquefaction processes.

Answer 1

The Correct Option is B

Concept: When a real gas undergoes a throttling process (Joule–Thomson process), enthalpy remains constant: \[ H = \text{constant} \] The temperature change with pressure under this condition is defined by: \[ \mu_{JT} = \left(\frac{\partial T}{\partial P}\right)_H \] This coefficient measures heating or cooling during expansion or compression at constant enthalpy.

Step 1: Identify process condition.
Given: \[ H = \text{constant} \] So we are dealing with throttling process.

Step 2: Apply definition.
\[ \mu_{JT} = \left(\frac{\partial T}{\partial P}\right)_H \]

Step 3: Physical meaning.
- Positive $\mu_{JT}$ → cooling on expansion - Negative $\mu_{JT}$ → heating on expansion Final Answer: \[ \boxed{\text{Joule–Thomson coefficient}} \]