For a sample of perfect gas, when its pressure is changed isothermally from p i to p f , the entropy change…

For a sample of perfect gas, when its pressure is changed isothermally from ${\mathrm{p}}_{\mathrm{i}}$ to ${\mathrm{p}}_{\mathrm{f}}$, the entropy change is given by $∆\mathrm{S}=\mathrm{n}\mathrm{R}\ln \left(\frac{{\mathrm{p}}_{\mathrm{i}}}{{\mathrm{p}}_{\mathrm{f}}}\right)$

Here, ${\mathrm{p}}_{\mathrm{i}}$ stands for initial pressure and ${\mathrm{p}}_{\mathrm{f}}$ stands for the final pressure.