Question

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:-

• A. $-508.9\,KJ\,mol^{-1}$
• B. $-2.8.1\,Kj\,mol^{-1}$
• C. $-269.9\,KJ\,mol^{-1}$
• D. $-358.5\,Kj\,mol^{-1}$

Answer 1

Answer: (B)

$-2.8.1\,Kj\,mol^{-1}$

Answer 2

$\because$ Heat of hydrogenation of cyclohaxene $=-119.5 kJ / mol$ $\therefore$ Heat of hydrogenation of benzene $=3 \times-119.5=-358.5 KJ / mol$ Resonance energy $=$ Observed $\Delta H -$ Calculated $\Delta H$ $-150.4=-358.5- x$ $x =-208.1\, KJ$