Answer to Question #208205 in Physical Chemistry for Yakubu

Question

The heat of combustion of benzene is -3268jmol and cyclohexane is -3920kjmol. 

Calculate: 

(a) The heat of hydrogenation of benzene to cyclohexane

(b)The heat required to hydrogenate a double bond of benzene

Answer 1

Heat of hydrogenation = -3268+ 3920 = 658kjmol

Benzene has three double bonds, so we might expect its heat of hydrogenation to be -360 kJ/mol. However, its measured heat of hydrogenation is only -208 kJ/mol. Benzene is more stable than expected by 152 kJ/mol. This difference is called its resonance energy.