Question

One mole of a monatomic ideal gas undergoes a cyclic process as shown in the figure (where $V$ is the volume and $T$ is the temperature). Which of the statements below is (are) true?

• A. Process I is an isochoric process
• B. In process II, gas absorbs heat
• C. In process IV, gas releases heat
• D. Processes I and II are not isobaric

Answer 1

Answer: (B), (C), (D)

Processes I and II are not isobaric

(A) Process-I is not isochoric, as we can see that $V$ is decreasing.

For option B:
Process-II is isothermal expansion
$\Rightarrow$ $\Delta U=0$ but $W>0$ as volume is increasing
By first law of thermodynamics
$\Delta Q$=$\Delta U+\Delta W$
$\Delta U=0(\therefore \Delta T=0)$
$\Rightarrow \Delta Q>0$
In this process heat will be absorbed. Hence option B is correct.

For option C:
Process-IV is isothermal compression,
$\Rightarrow$ $\Delta U=0$ but $W<0$ as volume is decreasing
$\Rightarrow$ $\Delta Q<0$
In this process heat will be rejected. Hence option C is correct.

For option D:
Process-I and III are not isobaric because in isobaric process $T\propto V$ hence isobaric $T-V$ graph will be linear.