Question

The enthalpy of hydrogenation of cyclohexene is $-119.5kJ/mol$. What is the enthalpy of benzene, if its resonance energy is $-150.4kJ/mol$?

• A. $-269kJ/mol$
• B. $-358.8kJ/mol$
• C. $-508.9kJ/mol$
• D. $-208.1kJ/mol$

Answer 1

The correct option is D $-208.1kJ/mol$

Enthalpy of hydrogentaion of cyclohexene = $-119.5kJ/mol$
$\therefore$ calculated enthalpy of hydrogenation of benzene is: $3(-119.5)=-358.5kJ/mol$
Since the actual value should be lower by an amount equal to resonance energy, actual enthalpy of hydrogenation is
$=-358.5kJ/mol-(-150.4kJ/mol)$
$=-208.1kJ/mol$