Question

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 1

`C_(6)H_(10)+H_(2) rarr C_(6)H_(12), DeltaH=-119kJ`
`(` involves breaking up of one double bond and addition of one `H_(2)` molecule `)`
`:. C_(6)H_(6)+3H_(2) rarr C_(6)H_(12), DeltaH=-119xx3=-357kJ`
`(` involves breaking up the three double bond and addition of three `H_(2)` molecule `)`
`6C+6H_(2) rarr C_(6)H_(12(l)), DeltaH=-156`
we have , `ul ({:(C_(6)H_(6),+3H_(2),rarr,C_(6)H_(12(l)),,DeltaH=-357),(-,-,,-,+):}) `
`6C+3H_(2) rarr C_(6)H_(6), DeltaH=+201kJ`
Therefore, Resonance energy
`=49-201=-152kJ`
`(Exp.) (` Theoretical `)`