Question

For the gas shown in the diagram, where is the exhaust heat released from the system when $70J$ of energy is added to the system?

• A. $A\to B$
• B. $B\to C$
• C. $C\to D$
• D. $D\to A$
• E. $A\to B\to C\to D\to A$

Answer 1

The correct option is C $C\to D$

Process CD is an isothermal process i.e $\Delta T_{CD}=0$ or $\Delta U_{CD}=0$

From figure, volume of the gas reduces during process CD, thus $W_{CD}<0$

Using 1st law of thermodynamics, $Q_{CD}=\Delta U_{CD}+W_{CD}$

$\therefore$ $Q_{CD}=0+W_{CD}$ $⟹Q_{CD}=W_{CD}<0$

Thus heat is released by the system during process $C\to D$.