The enthalpy of hydrogenation of cyclohexene | vedclass

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Question

(B) The enthalpy of hydrogenation of cyclohexene is $-119.5 \ kJ \ mol^{-1},$ which corresponds to the hydrogenation of one $C=C$ double bond.Benzene

Vedclass · Accepted Answer

$-508.9$

Vedclass · Answer

(B) The enthalpy of hydrogenation of cyclohexene is $-119.5 \ kJ \ mol^{-1},$ which corresponds to the hydrogenation of one $C=C$ double bond.Benzene contains three $C=C$ double bonds. Therefore,the calculated enthalpy of hydrogenation for benzene (assuming no resonance) is:$\Delta H_{Cal} = 3 	imes (-119.5 \ kJ \ mol^{-1}) = -358.5 \ kJ \ mol^{-1}.$Resonance energy is defined as the difference between the experimental enthalpy of hydrogenation and the calculated enthalpy of hydrogenation:$	ext{Resonance Energy} = \Delta H_{Exp} - \Delta H_{Cal}.$Given that the resonance energy is $-150.4 \ kJ \ mol^{-1},$ we have:$-150.4 = \Delta H_{Exp} - (-358.5).$Solving for $\Delta H_{Exp}:$$\Delta H_{Exp} = -150.4 - 358.5 = -508.9 \ kJ \ mol^{-1}.$

The enthalpy of hydrogenation of cyclohexene is $-119.5 \ kJ \ mol^{-1}.$ If resonance energy of benzene is $-150.4 \ kJ \ mol^{-1},$ its enthalpy of hydrogenation would be $...... \ kJ \ mol^{-1}.$

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