The enthalpies of combustion of carbon and carbon monoxide are $-393.5 \mathrm{and} -283.5 \mathrm{kJ} {\mathrm{mol}}^{-1}$ respectively. The enthalpy of formation of carbon monoxide per mole is

$$\begin{gathered} \mathrm{C} + {\mathrm{O}}_2 \to {\mathrm{CO}}_2; ∆\mathrm{H}=-393.5 \mathrm{kJ} \\ \mathrm{CO}+\raisebox{1ex}{$1$}\!\left/ \!\raisebox{-1ex}{$2$}\right.{\mathrm{O}}_2 \to {\mathrm{CO}}_2; ∆\mathrm{H}=-283.5 \mathrm{kJ} \\ - - - + \\ \mathrm{\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_} \\ \mathrm{C} + \raisebox{1ex}{$1$}\!\left/ \!\raisebox{-1ex}{$2$}\right.{\mathrm{O}}_2 \to \mathrm{CO}; ∆\mathrm{H}=-110.5 \mathrm{kJ} \end{gathered}$$