Question

For a sample of perfect gas when its pressure is changed isothermally from Pᵢ to Pf, the entropy change is given by
(1) ∆S= nR ln(Pf/Pᵢ)
(2) ∆S= nR ln(pᵢ/pf)
(3) ∆S= nRT ln(pf/p'ᵢ)
(4) ∆S= RT ln(pᵢ/pf)

Answer 1

Answer: option 2

Explanation:

ΔS = nCpln(T2/T1) + nRln(Pi/Pf)

Since it is isothermal so T2/T1 = 1 so Ln(1) = 0)

Hence

ΔS = nRln(Pi/Pf)