The reaction MgO(s) + C(s) $\to$ Mg(s) + CO(g), for which ${\Delta }_r{H}^o=+491.1$kJ mol^–1 and ${\Delta }_r{S}^o=198.0$ JK^–1mol^–1, is not feasible at 298 K. Temperature above which reaction will be feasible is