Question

Temperature of a system decreases during

• A. Isothermal compression
• B. Adiabatic compression
• C. Adiabatic expansion
• D. Isothermal expansion

Answer 1

The correct option is C Adiabatic expansion

In adiabatic systems, there is no heat exchanged with the system and the surrounding since $q=0$. Hence, $\Delta U=w$
So the temperature would decrease if the internal energy decreases, since $\Delta U$ is directly proportional to $\Delta T$.
this means that the gas would expand! This is a direct consequence of the fact that $w=-P\Delta V$ if $w$ has to have a -ve value, then the final volume MUST be greater than the initial volume.