Question

For the isothermal expansion of an ideal gas in a piston cylinder system, the net heat supplied during the process is equal to the net work. Which one of the following statements is correct for the given process?

• A. The process is possible.
• B. The process is not possible as it violates the second law of thermodynamics.
• C. The process is not possible as it violates the first law of thermodynamics.
• D. The process is possible, however, it violates the second law of thermodynamics.

Hint:

Recall that internal energy of an ideal gas depends only on temperature, and see what that means when temperature stays constant.

Answer 1

The Correct Option is A

This question checks whether "heat supplied equals work done" in an isothermal expansion is some special or forbidden condition, or just ordinary behaviour.

1. The process is possible: correct. For an ideal gas at constant temperature, internal energy does not change, so the first law reduces to Q = W with no extra assumption needed.
2. Not possible, violates the second law: wrong. A reversible isothermal exchange with a reservoir at the gas temperature gives zero net entropy change, so the second law holds fine.
3. Not possible, violates the first law: wrong. Q = W is the direct result of the first law here, not a violation of it.
4. Possible but violates the second law: wrong, since nothing about this process breaks the second law either.

Because Q = W is exactly what the first law demands for isothermal ideal gas expansion, the process is possible, so option (A) is correct.