The enthalpies of combustion of carbon and carbon monoxide in excess of oxygen at `298K` and constant pressure are `-393.5` and `-283.0 kJ mol^(-1)`, respectively. Calculate the heat of formation of carbon monoxide at constant volume.

Explanation

`C(s) +(1)/(2)O_(2)(s) rarr CO(s) DeltaH = ?`
Given:
`C(g) +O_(2)(g) rarr CO_(2)(g), DeltaH_(1) = - 393.5 ….(i)`
`CO(g) +(1)/(2)O_(2)(g) rarr CO_(2)(s), DeltaH_(2) =- 283 …(ii)`
`Delta_(f)H = DeltaH_(1) - DeltaH_(2)`
`= 393.5 -(-283) =- 110.5 kJ`
`Deltan_(g) = 1 - (1)/(2)=(1)/(2)`
`DeltaU^(Theta) = DeltaH - Deltan_(g)RT`
`= - 11.05 -(-(1)/(2)) xx 8.314 xx 10^(-3) xx 298`
`=- 111.7 kJ mol^(-1)`