Question

Which combination of the following statements is correct?
P: A gas cools on expansion only when its Joule-Thomson coefficient is positive in the temperature range of expansion
Q: For a system undergoing a process, its entropy remains constant only when the process is reversible.
R: The work done by a closed system in an adiabatic is a point function.
S: A liquid expands upon freezing when the slope of its fusion curve on the Pressure-Temperature diagram is negative.

• A. P, Q and R
• B. R and S
• C. P and Q
• D. Q, R and S

Answer 1

The correct option is B R and S

From the figure, we can say that the Joule-Thomson coefficient is positive in the temperature range of expansion. So the statement is correct.

Q: Entropy is constant when the process is reversible adiabatic, not only reversible, so statement is wrong.

R: From first law of thermodynamics,
$\delta Q=dU+\delta W$

For adiabatic process,
$\delta Q=0$
$dU=-\delta W$

Since dU is a point function, we can say work done by a closed system in an adiabatic is a point function. So the statement is correct.

Liquid expands upon freezing only when the liquid is water and in this case, slope of fusion curve on P-T diagram is negative. So the statement is correct. So, the statements P, R and S are correct. So option (a) is correct