The standard molar enthalpies of formation of cycohexane (l) and benzene (l) at 25 ° C are -156 and +49 KJ m o l - 1 respectively. The standard enthalpy of hydrogenation of cyclo hexene (l) at 25 ° C

Question

The standard molar enthalpies of formation of cycohexane (l) and benzene (l) at 25 ° C are -156 and +49 KJ m o l - 1 respectively. The standard enthalpy of hydrogenation of cyclo hexene (l) at 25 ° C is -116 KJ m o l - 1 . Use these data to estimate the magnitude of the resonance energy of benzene.

TestHub · Accepted Answer

Enthalpy of hydrogenation of these double bond in benzene
$= 3 \times - 119 = - 357 kJ {mol}^{- 1}$
$ΔH(reaction) = ΣH(products) - ΔΣH(reactants)$
$= - 156 - (49 + 0) = - 205 kJ {mol}^{- 1}$
Resonance energy = Calculated heat of hydrogenation – Actual heat of hydrogenation
$= 357 - 205 = 152 kJ {mol}^{- 1} .$

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