The standard molar enthalpies of formation of cyclohexane (l) and benzene (l) at `25^(@)C` are `-156` and `+49 kJ mol^(-1)`, respectively. The standard enthaly of hydrogenation of cyclohenxene (l) at `25^(@)C` is `-119 kJ mol^(-1)` Use this data to estimate the magnitude of the resonance enegry of benzene.

Answer

`-152 kJ`

Explanation

`C_(6)H_(1) + H_(2) rarr C_(6) H_(12) , Delta H = - 119 kJ`
(involves breaking up of three double bond and additional of three `H_(2)` molecule)
`:. C_(6) H_(6) + 3H_(2) rarr C_(6) H_(12) , Delta H = 3 xx (-119) = - 357 kJ`
(involves breaking up of three double bond and additional of three `H_(2)` molecule)
Also given `6 C + 6 H_(2) rarr C_(6) H_(12) (l0 , Delta H = - 156`
We have `C_(6) H_(6) + 3H_(2) rarr C_(6)H_(12) (l) , Delta H = - 357 6 C + 3H_(2) rarr C_(6)H_(6) , Delta H + 201 kJ`
Therefore, resonace energy `= 49 - 201 = 152 kJ`