Given that C+O2→CO2; ∆H0=-x kJ and 2CO+ O2→2CO2; ∆H0=-y kJThe enthalpy of formation of carbon monoxide will be

We have to get the relation C+O2→CO2-x kJ Consider equation 1-12 equation 2,i.e.,   C+O2→CO2-x kJ               …..(1)-CO+12O2→CO2-y2 kJ        ……(2)or      C-CO+12O2→zero+-x+y2 or      C+12O2→CO.y-2x2