-f H- of Cyclohexene l and benzene at 25-C is -156 and -46 kJ mol -1- respectively- - hydrogenation H- of Cyclohexene l at 25-C is -119 kJ mol -1-Resonance energy of benzene is found to be -38x kJ mol -1- Find the value of x-

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Standard X

Chemistry

Covalent Bond

Δf H⊖ of Cycl...

Question

$Δ_{f} H^{⊖}$ of Cyclohexene $(l)$ and benzene at $25^{\circ} C$ is $- 156$ and $+ 46 k J m o l^{- 1}$ , respectively.
$Δ_{h y d r o g e n a t i o n} H^{⊖}$ of Cyclohexene $(l)$ at $25^{\circ} C$ is $- 119 k J m o l^{- 1}$ .
Resonance energy of benzene is found to be $- 38 x k J m o l^{- 1}$ . Find the value of x.

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Solution

The correct option is A 4
This shows that the generation of one $(C = C)$ bond in Cychlohexene requires $119 k J m o l^{- 1}$ of enthalpy. TO calculate RE resonance energy.
$Δ H_{1}^{⊖} = Δ H_{2}^{⊖} = Δ H_{3}^{⊖} = 119 k J m o l^{- 1}, Δ H_{4}^{⊖} = R E$
$Δ H_{5}^{⊖} = Δ_{f} H^{⊖} (b e n z e n e) - Δ_{f} H^{⊖} (c y c l o h e x e n e)$
$= 46 - (- 156) = 205 k J m o l^{- 1}$
$∴ F r o m H e s s ‘ l a w :$
$Δ H_{4}^{⊖} = Δ H_{5}^{⊖} - (Δ H_{1}^{⊖} + Δ H_{2}^{⊖} + Δ H_{3}^{⊖})$ .
$= 205 - 3 \times 119 = - 152 k J m o l^{- 1}$
$∴ - 38 x = - 152$
$x = 4$

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Similar questions

Q. The standard molar enthalpies of formation of cyclohexane

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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.

Q. The standard molar enthalpies of hydrogenation of benzene (

l

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- 208 {kJ mol}^{- 1}

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(correct answer +1, wrong answer -0.25)

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ΔfH⊖ of Cyclohexene (l) and benzene at 25∘C is −156 and +46kJmol−1, respectively. ΔhydrogenationH⊖ of Cyclohexene (l) at 25∘C is −119kJmol−1.Resonance energy of benzene is found to be −38xkJmol−1. Find the value of x.