Standard molar entropies of Mg(s), C(s), MgO(s) and CO(s) are ${\mathrm{S}}_1,{\mathrm{S}}_2,{\mathrm{S}}_3\mathrm{and}{\mathrm{S}}_4$
J/K/mol .then $\mathrm{\Delta }{\mathrm{S}}_{\mathrm{sys}}\mathrm{for}{\mathrm{MgO}}_{\left(\mathrm{s}\right)}+{\mathrm{C}}_{\left(\mathrm{s}\right)}\to {\mathrm{Mg}}_{\left(\mathrm{s}\right)}+{\mathrm{CO}}_{\left(\mathrm{g}\right)}$