Question

The enthalpy of hydrogenation of cyclohexene is `-119.5kJ mol^(-1)`. If resonance energy of benzene is `-150.4kJ mol^(-1)`, its enthalpy of hydrogenation would be `:`
A. `-269.9 kJ mol^(-1)`
B. `-358.5 kJ mol^(-1)`
C. `-508.9 kJ mol^(-1)`
D. `-208.1 kJ mol^(-1)`

Answer 1

Correct Answer - D
Enthalpy of hydrogenation of cyclohexene
`=-119.5 kJ mol^(-1)`
`:. "calculated enthalpy of hydrogenation of benzene"` `=3(-119.5)=-358.5 kJ mol^(-1)`
Since the actual value is lower by an amount equal to resonance energy hence, actual enthalpy of hydrogenation
`=-358.5 kJ mol^(-1)-(-150.4 kJ mol^(-1))`
`=-208.1 kJ mol^(-1)`