The heat liberated on complete combustion of `7.8g` benzene is `327kJ`. This heat has been measured at constant volume and at `27^(@)C`. Calculate heat of combustion of benzene at constant pressure at `27^(@)C`. `(R=8.3 J mol^(-1)K^(-1))`

Explanation

Heat of combustion fo benzene at constant pressure,
`DeltaH = (327)/(7.8) xx 78 =- 3270 kJ mol^(-1)`
`C_(6)H_(6)(l)+(15)/(2)O_(2)(g) rarr 6CO_(2)(g) +3H_(2)O(l)`
`Deltan_(g) = 6 -(15)/(2) =- (3)/(2)`
`DeltaH = DeltaU +Deltan_(g)RT`
or `DeltaU = DeltaH - Deltan_(g)RT`
`=- 3270 - (3)/(2) xx (8.3)/(1000) xx 300 =- 3266.265 kJ`