Chapter 18 - Heat Engines and Refrigerators - Exercises and Problems - Page 549: 10

See the detailed answer below.

$\bullet$ Process A: is an adiabatic expansion process. This means that there is no heat exchange during this process. So, $Q=0$. And as we see in this process the gas expands, which means that the work is positive. We can see that the temperature decreases which means the thermal energy decreases. $\bullet$ Process B: is an isochoric process. This means that the volume is constant and hence the work done on the system is zero. And as we see the pressure increases, and also the temperature increases. Thus, the thermal energy increases as well. And since $\Delta E_{th}=Q+W$, and $W=0$, then $Q$ increases. $\bullet$ Process C: is an isothermal compression process. This means that the temperature is constant. The volume of the gas decreases which means that the work is negative. \begin{array}{|c|c|c|c|} \hline & \Delta E_{th}& W&Q\\ \hline \rm A& - & +&0 \\ \hline \rm B & + & 0 &+\\ \hline \rm C & 0 & -&- \\ \hline \end{array}