1. Hess’s law can be applied to calculate the enthalpy of formation of carbon monoxide. It is very difficult to control the oxidation of graphite to give pure CO.
However, enthalpy for the oxidation of graphite to CO2 can be easily measured and enthalpy of oxidation of CO to CO2 is also measurable.
2. The application of Hess’s law enables us to estimate the enthalpy of formation of CO.
C + O2 → CO2∆H° = 393.5 kJ ….. (1)
CO + 1/2 O2 → CO2 ∆H° = -283 kJ ….. (2)
On inverting equation (2), we get
CO2 → CO + 1/2 O2 ∆H° = + 283 kJ …… (3)
On adding equations (2) and (3), we get
C + 1/2 O2 → CO ∆H° = 393 5 + 283 = 110.5kJ
