The standard molar enthalpies of formation of cyclohexane $(l)$ and benzene $(l)$ at $25^{o} C$ are $- 156$ and $+ 49$ $k J m o l^{- 1}$ respectively. The standard enthalpy of hydogenation of cyclohexene $(l)$ at $25^{o} C$ is $- 119 k J m o l^{- 1}$ .
Use these data to estimate the magnitude of resonance energy of benzene in $k J / m o l$ .

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Solution

The reactions given in question are:

and enthalpy of hydrogenation of 1 double bond given as $Δ H$ = $- 119 k J / m o l$
so, for 3 double bonds $Δ H =$ $(- 119 \times 3) =$ $- 357 k J / m o l$

and $Δ H$ for the conversion of benzne to cyclohexane is
$= - 156 - 49$
$= - 205 k J / m o l$

hence, Resonance energy = $- 357 - (- 205)$
$= - 152 k J / m o l$

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Q. The standard molar enthalpies of formation of cyclohexane

(l)

and benzene

(l)

25^{o} C

are

- 156

and

+ 49 k J {m o l}^{- 1}

respectively. The standard enthalpy of hydrogenation of cyclohexene

(l)

25^{o} C

- 119 k J {m o l}^{- 1}

. Use these data to estimate the magnitude of resonance energy of benzene.

The standard molar enthalpies of formation of cyclohexane (l) and benzene (l) at $25^{\circ} C$ are -156 and +49 kJ/mol. The standard enthalpy of hydrogenation of cyclohexene (l) at $25^{\circ} C$ is -119 kJ/mol. Estimate the magnitude of resonance energy.