Question

A vessel contains an ideal monoatomic gas which expands at constant pressure, when heat $Q$ is given to it. What is the work done?

• A. $Q$
• B. $\frac{3}{5}Q$
• C. $\frac{2}{5}Q$
• D. $\frac{2}{3}Q$

Answer 1

The correct option is C $\frac{2}{5}Q$

For monoatomic gas,$C_p=\frac{5R}{2},C_v=\frac{3R}{2}$
Hence for isobaric process, heat given=$Q=\frac{5}{2}nR\Delta T=\frac{3}{2}nR\Delta T+W$
$\Rightarrow W=nR\Delta T=\frac{2}{5}Q$