Q. Heat of dissociation of benzene of elements is 5335 kJ/mol. The bond enthalpies of $|\ \ \ \ \ \ |\ \ \ \ \ \ |\ \ \ \ \ \ \ \ |$ $|$ $–C - C - ;C = C$ and $–C - H$ $|\ \ \ \ \ \ |\ \ \ \ \ \ |\ \ \ \ \ \ \ \ |$ $|$ bonds are 347.3, 615 and 416.2 kJ respectively. Resonance energy of benzene is
A) 1.15 kJ
B) 15.1 kJ
C) 937.2 kJ
D) 1511 kJ
Explanation
(c)
First we calculate the expected bond dissociation energy of benzene molecules as
$3 \times C - C + 3 \times C = C + 6 \times C - H$
$\therefore$ Calculated value $= 3(347.3) + 3(615) + 6(412.2)$
$= 4397.8$
Resonance energy = Experimental value $–$ calculated value
$= 5335 - 4397.8$
$= 937.2\$ kJ per mol
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.