UPSEE Solved Model Paper 3

Direction : The bond dissociation energy of a diatomic molecule is also called bond energy. Bond energy is also called, the heat of formation of the bond from the gaseous atoms constituting the bond with reverse sign.
Example : H (g) + Cl (g) → H - Cl (g) , ΔHf = −431kJmol−1 or bond energy of H - Cl = −(ΔHf) = - (431) = + 431 kJ mol−1. When a compound shows resonance there occurs a fair agreement between the calculated values of heat of formation obtained from bond enthalpies and any other method. However deviation occur insane of compounds having alternate double bonds.
Example :

C6H6

(g)

→

6C

(g)

+

6H

(g)

Resonance energy = experimental heat of formation - calculated heat of formation
The polymerization of ethylene to linear polyethylene is represented by the reaction nCH2=CH2→(−CH2−CH2−)n when 'n' has a large integral value. Given that average enthalpies of bond dissociation for C=C and C−C at 298K are + 590 and + 331 kJ mol−1 respectively. Then the enthalpy of polymerization/mol of ethylene at 298 K