Question

The wrong statement among the following is

• A. During free expansion, temperature of ideal gas does not change
• B. During free expansion, temperature of real gas decreases
• C. During free expansion of real gas temperature does not change
• D. Free expansion is conducted in adiabatic manner

Hint:

Free expansion: $\Delta U=0, Q=0, W=0$. Ideal gas $\Delta T=0$. Real gas $\Delta T \neq 0$.

Answer 1

The Correct Option is C

Step 1: Concept
Free expansion is an adiabatic process ($Q=0$) where work done ($W$) is zero because the gas expands into a vacuum.

Step 2: Meaning
By the first law ($\Delta U = Q - W$), $\Delta U = 0$. For an ideal gas, $U$ depends only on $T$, so temperature remains constant.

Step 3: Analysis
For real gases, internal energy includes potential energy between molecules. As they expand, potential energy increases, so kinetic energy (and thus temperature) must decrease to keep $\Delta U = 0$.

Step 4: Conclusion
Statement (C) is wrong because the temperature of a real gas does change (it usually decreases) during free expansion. Final Answer: (C)