Question

For an ideal gas undergoing an isothermal process, which of the following remains constant?

• A. Pressure
• B. Temperature
• C. Volume
• D. Entropy

Hint:

{Isothermal = Constant Temperature}. Always associate “iso” with “same” in thermodynamics.

Answer 1

The Correct Option is B

Step 1: Meaning of isothermal process.
An isothermal process is a thermodynamic process in which the temperature of the system remains constant throughout the process. The term “iso” means same, and “thermal” refers to temperature.
Step 2: Ideal gas behavior.
For an ideal gas, the equation of state is given by: \[ PV = nRT \] During an isothermal process, the temperature $T$ remains constant while pressure and volume may change.
Step 3: Effect on other properties.
- Pressure varies inversely with volume.
- Volume changes with pressure.
- Entropy may change depending on heat transfer.
However, temperature remains unchanged by definition.
Step 4: Analysis of options.
(A) Pressure: Incorrect — Pressure changes during an isothermal process.
(B) Temperature: Correct — Temperature remains constant throughout the process.
(C) Volume: Incorrect — Volume changes to maintain constant temperature.
(D) Entropy: Incorrect — Entropy can change during isothermal processes.
Step 5: Conclusion.
Since an isothermal process is defined by constant temperature, the correct answer is temperature.