For a reversible process involving ideal gases in a closed system, show that
ΔS = C_{v} ln(T_{2}/T_{1}) for a constant volume process
ΔS = C_{p} ln(T_{2}/T_{1}) for a constant pressure process
ΔS = R ln(V_{2}/V_{1}) = R ln(P_{1}/P_{2}) for an isothermal process