Chapter 18 - Heat Engines and Refrigerators - Exercises and Problems - Page 549: 9

See the detailed answer below.

$\bullet$ Process A: 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 B: is an adiabatic 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 C: is an isothermal process. This means that the temperature is constant. The volume of the gas increases which means that the work is positive. And since the thermal energy is constant, then the system absorbs heat. $\bullet$ Process D: is an isobaric process. This means that the pressure is constant. The volume of the gas decreases which means that the work is negative. The temperature decreases, so the thermal energy decreases. Also, the heat is lost from the system. \begin{array}{|c|c|c|c|} \hline &\Delta E_{th} &W_S &Q \\ \hline \rm A &+ &0 &+\\ \hline \rm B &-& + &0\\ \hline \rm C &0 & + &+ \\ \hline \rm D & -& -& - \\ \hline \end{array}