Question

Statement 1: Temperature of Real gases often changes when undergoing a free expansion under adiabatic condition whereas that of an ideal gas does not.

Statement 2: First law of thermodynamics holds for ideal gas only.

• A. Statement 1 is true. Statement 2 is true and statement 2 is correct explanation for statement 1.
• B. Statement 1 is true. Statement 2 is true and statement 2 is NOT correct explanation for statement 1.
• C. Statement 1 is true. Statement 2 is false
• D. Statement 1 is false. Statement 2 is true.

Answer 1

The correct option is C Statement 1 is true. Statement 2 is false

For ideal gas, change in internal energy=$\Delta U\propto \Delta T$
During free adiabatic expansion,$\Delta Q=\Delta W=0\Rightarrow \Delta U=0\Rightarrow \Delta T=0$
However for real gases, $\Delta U=f(V,T)$
In this case, for free adiabatic expansion $\Delta U=0\Rightarrow f(V,T)=0$
Thus T may change in this case.
Hence statement-1 is true.

However first law always holds irrespective of the nature of the gas undergoing the process.
Hence, statement-2 is false.