Question

If one mole of an ideal gas $(C_{p,m}=\frac{5}{2}R)$ is expanded isothermally at 300 K, until it's volume is tripled, then, change in entropy of gas is :

• A. $0$
• B. $\infty$
• C. $\frac{5}{2}R\ln 3$
• D. $R\ln 3$

Answer 1

The correct option is D $R\ln 3$

$\Delta S=Cv\times \ln \left(\frac{T2}{T1}\right)+R\times \ln \left(\frac{V2}{V1}\right)$

At constant temperature,

$\Delta S=R\times \ln \frac{V2}{V1}=R\times \ln \frac{3V}{V}=R\ln 3$