Question

For an isothermal free expansion of an ideal gas into vacuum, which one of the following set correct?

• A. $\Delta U=0, q > 0, w < 0$
• B. $\Delta U =0, q > 0, w =0$
• C. $\Delta U=0, q=0, w=0$
• D. $\Delta U < 0, q=0, w < 0$

Answer 1

Answer: (C)

For isothermal process, $\Delta T =0 .$ For an ideal gas, internal energy U depend only on temperature.

So, $\Delta U=0$

Now $\Delta U=q + w$

$q=-w=P \Delta U$

For free expansion $P_{\text {ext }}=0$

So, $q=-w=0$

$\therefore \Delta U=0, q=0, w=0$