Question

The enthalpy of hydrogenation of cyclohexene is119.5 kJ/mol. If resonance energy of benzene is 150.4 kJ/mol, its enthalpy of hydrogenation would be:

• A. 508.9 kJ/mol
• B. 208.1 kJ/mol
• C. 269.9 kJ/mol
• D. 358.5 kJ/mol

Answer 1

Answer: (B)

208.1 kJ/mol

The Hydrogenation of cyclohexene forms cyclohexane

$C_6$$H_{10}$ + $H_2$ $\to C_6{H}_{12}$

As the breaking of 1 C=C Bond and the formation of 2 C-H Bonds has a net release of 119.5 kJ/mol,

So, in the case of benzene, 3 C=C bonds is hydrogenated by $3\times 119.5kJ/mol=358.5kJ/mol$.

Since benzene has resonance energy, the enthalpy change of hydrogenation is $358.5-150.4kJ/mol=208.1kJ/mol$

Therefore, the correct option is $B$