The equilibrium box

The meaning of the once widely used term the Gibbs Free Energy in terms of available work energy is perfectly illustrated for chemical reactions by the Van’t Hoff Equilibrium Box. Combining this with DeDonder’s extent of reaction variable and using the reaction of \(\hbox {NH}_3\) ${\text{NH}}_3$ to \(\hbox {H}_2\) ${\text{H}}_2$ and \(\hbox {N}_2\) ${\text{N}}_2$ at \(200^{\circ }\hbox {C}\) ${200}^{\circ }\text{C}$ as an example shows the difference between total work energy and available work energy, and in addition allows calculation of the equilibrium composition, demonstration of the minimum in the Gibbs energy curve, and the standard relationship between \(\Delta _\textrm{r}G^{\circ }\) ${\mathrm{\Delta }}_{\text{r}}{G}^{\circ }$ and \(\ln {K}\) $lnK$