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

Question

The standard molar enthalpies of formation of cycohexane (l) and benzene (l) at 25° C are -156 and +49 KJ mol- 1 respectively. The standard enthalpy of hydrogenation of cyclo hexene (l) at 25° C is -116 KJ mol- 1 . Use these data to estimate the magnitude of the resonance energy of benzene. (A)  text152 textkJ textmol- 1 (B) 1.52 textkJ textmol- 1 (C) 15.2 textkJ textmol- 1 (D) None of these

Tardigrade Admin · 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} .

$152 kJ mol^{- 1}$

$1.52 kJ mol^{- 1}$

$15.2 kJ mol^{- 1}$

None of these

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

152kJmol−1

1.52kJmol−1

15.2kJmol−1

None of these

Enthalpy of hydrogenation of these double bond in benzene =3×−119=−357kJmol−1 ΔH(reaction)=ΣH(products)−ΔΣH(reactants) =−156−(49+0)=−205kJ(mol)−1 Resonance energy = Calculated heat of hydrogenation - Actual heat of hydrogenation =357−205=152kJmol−1.

$152 kJ mol^{- 1}$

$1.52 kJ mol^{- 1}$

$15.2 kJ mol^{- 1}$