The amount of heat evolved during complete combustion of 7.8 g benzene at constant volume and `27^(@)C` is 3270 kJ. Calculate heat of combustion of benzene at constant pressure and `27^(@)C`.

Explanation

`7.8 g C_(6)H_(6)=(7.8)/(78)= 0.1 " mol " C_(6)H_(6)`
Heat of combustion for 0.1 mol of benzene at constant volume is 3270 kJ. Hence, heat of combustion for 1 mol of benzene at constant volume `= (3270 kJ)/(0.1)= 32700 kJ`
`C_(6)H_(6)(l)+(15)/(2)O_(2)(g) to 6CO_(2)(g)+3H_(2)O(l), Delta n= 6-(15)/(2)= -(3)/(2)`
`Delta H= Delta U+ Delta n RT`
`= (32700 - (3)/(2)xx8.314xx300xx10^(-3) kJ`
`= - 32696.26 kJ`