Calculate the difference between heats of reaction at constant pressure and constant volume for the following reaction at `25 ^(@)C, 2C (6) H _(6) (l) + 15 O _(2) (g) to 12 CO _(2) (g) + 6 H _(2) O (l).`

Explanation

Heat of reactio at constant pressure, `Delta H` and at constant volume, `Delta U` are related as :
`Delta H = Delta U + Delta n _(g) RT or Delta H - Delta U = Delta n _(g) RT`
Here, `Delta n _(g) = 12 mol - 15 mol =- 3 mol, T = 25 ^(@)= 298 K, R = 8.314 JK ^(-1) mol ^(-1)`
`Delta H - Delta U = Delta n _(g) RT - 3 mol xx 8. 314 JK ^(-1) mol ^(-1) xx 298 K =- 7433 J =- 7.433 kJ`