Question

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

• A. $-269.9kJ{mol}^{-1}v$
• B. $-358.5kJ{mol}^{-1}$
• C. $-508.9kJ{mol}^{-1}$
• D. $-208.1kJ{mol}^{-1}$

Answer 1

The correct option is D $-208.1kJ{mol}^{-1}$

Solution:- (D) $-208.1kJ/mol$

Enthalpy of hydrogentaion of cyclohexene $=-119.5kJ/mol$

$\therefore$ calculated enthalpy of benzene $=3\times (-119.5)=-358.5kJ/mol$

Resonance energy of benzene $=-150.4kJ/mol$

As we know that

Actual value of enthalpy $=$ calculated enthalpy $-$ resonance energy

$\therefore$ Actual enthalpy of benzene $=(-358.5)-(-150.4)=-208.1kJ/mol$

Hence the enthalpy of hydrogenation of benzene is $-208.1kJ/mol$.