The enthalpies of combustion of carbon and carbon monoxide are -393.5 and -283.5 kJ mol-1 respectively. The enthalpy of formation of carbon monoxide per mole is

C + O2 → CO2; ∆H=-393.5 kJ CO+12O2 → CO2; ∆H=-283.5 kJ -       -                -                  + ________________________________ C + 12O2 → CO; ∆H=-110.5 kJ