question_answer

The enthalpy of hydrogenation of cyclohexene is\[-119.5\text{ }kJ\text{ }mo{{l}^{-1}}\]. If resonance energy of benzene is\[-150.4\text{ }kJ\text{ }mo{{l}^{-1}}\], its enthalpy of hydrogenation would be

A) \[-208.1kg\text{ }mo{{l}^{-1}}\]           

B) \[-269.9\text{ }kg\text{ }mo{{l}^{-1}}\]

C) \[-358.5\text{ }kg\text{ }mo{{l}^{-1}}\]

D) \[-508.9\text{ }kg\text{ }mo{{l}^{-1}}\]

Correct Answer: A

Solution :

[a] \[=-358.5\,KJ\] The resonance energy provides extra stability to the benzene molecule so it has to be overcome for hydrogenation to take place. So \[\Delta H=-358.5-\left( -150.4 \right)=-208.1\text{ }kJ\]