Q.
The heats of combustion of graphite and carbon monoxide, respectively are, −393.5kJmol−1 and −283kJmol−1 . Therefore, the heat of formation of carbon monoxide in, kJmol−1 is:
Combustion of graphite is as follows: C(s)+O2(g)CO2(g)+393.5kJ ...(i)
Combustion of carbon monoxide is, CO(g)+21(g)CO2(g)+283kJ ...(ii)
For obtaining CO as a product we reverse the Eq. (ii)
as CO2(g)CO(g)+21O2(g)−283kJ ...(iii) C(g)+O2(g)CO2(g)+393.5kJ ...(iv)
On adding Eq. (i) and Eq. (iii) C+21O2CO+(393.5−283) =+110.5kJ ∴ Heat of formation of CO is =+110.5kJ ∴ΔH=−110.5kJ