The standard free energy of formation$\mathrm{MgO}$ and $\mathrm{CO}$ at temperature 1000° C and 2000° below C (they refer to the reaction involving one mole of oxygen at one atmosphere pressure).

The free energy change to the reaction.

$\begin{array}{r}2\mathrm{Mg}+{\mathrm{O}}_2\to 2\mathrm{MgO}{\mathrm{\Delta G}}_{{1000}^{\circ }\mathrm{C}}=-941\mathrm{kJ}/\mathrm{mol}\\ {\mathrm{\Delta G}}_{{2000}^{\circ }\mathrm{C}}=-341\mathrm{kJ}/\mathrm{mol}\end{array}$

$\begin{array}{r}2\mathrm{C}+{\mathrm{O}}_2\to 2\mathrm{CO}{\mathrm{\Delta G}}_{{1000}^{\circ }\mathrm{C}}=-439\mathrm{kJ}/\mathrm{mol}\\ {\mathrm{\Delta G}}_{{2000}^{\circ }\mathrm{C}}=-628\mathrm{kJ}/\mathrm{mol}\end{array}$

The following reaction is feasible at :

$2\mathrm{MgO}+2\mathrm{C}⟶2\mathrm{Mg}+2\mathrm{CO}$