For a chemical process  $\mathrm{P}+\mathrm{Q}\to \mathrm{R}$, S⁰ values at 298 K for R, P and Q are 342 J.mol^-1 K^-1, 144 J.mol^-1 K^-1 and 72 J.mol^-1 K^-1 respectively. The energy not available to do useful work is

$$\begin{gathered} \mathrm{P}+\mathrm{Q}\to \mathrm{R} \\ {∆}^0\mathrm{S}={\mathrm{S}}_{\mathrm{products}}^0-{\mathrm{S}}_{\mathrm{reactants}}^0 \\ {∆}^0\mathrm{S}=\left[342-\left(144+72\right)\right] \mathrm{J}.{\mathrm{mol}}^{-1} {\mathrm{K}}^{-1} \\ {∆}^0\mathrm{S}=126 \mathrm{J}.{\mathrm{mol}}^{-1} {\mathrm{K}}^{-1} \\ \mathrm{Energy} \mathrm{not} \mathrm{available} \mathrm{to} \mathrm{do} \mathrm{useful} \mathrm{work} =\mathrm{T}{∆}^0{\mathrm{S}}_{\mathrm{system}} \\ \mathrm{Energy} \mathrm{not} \mathrm{available} \mathrm{to} \mathrm{do} \mathrm{useful} \mathrm{work} =298 \mathrm{K} \times 126 \mathrm{J}.{\mathrm{mol}}^{-1} {\mathrm{K}}^{-1} \\ \mathrm{Energy} \mathrm{not} \mathrm{available} \mathrm{to} \mathrm{do} \mathrm{useful} \mathrm{work} =37.548 \mathrm{kJ}/\mathrm{mole} \end{gathered}$$