Question

The standard molar enthalpies of formation of cyclohexane (I) and benzene(I) at `25^(@)C` are `-156` and `+49 KJ mol^(-1)` respectivelyl. The standard enthalpy of hydrogentation of cyclohexene (I) at `25^(@)` is `-119 KJ mol^(-1)`. Use these data to estimate the magnitude of the resonance energy of benzene.

Answer 1

Enthalpy of formation of `3` carbon-carbon double bonds
`= -156-(+49)KJ= -205 KJ`
Given that,
Theoretical enthalpy of formation of `3` double bonds in benzene ring
`=3xx(-119)KJ= -357KJ`
`:.` resonance energy of benzene `= -357-(-205)KJ= -152 KJ "mole"^(-1)`