Question

The polymerization of ethylene to linear polyethylene is represented by the reaction, 

n[CH₂ = CH₂] ----> [CH₂ -CH₂]_n

where, n has large integral value. Given that the average enthalpies of bond dissociation for C=C and C-C at 298 K are +590 and +331 kJ mol^-1 respectively, calculate the enthalpy of polymerization per mol of ethylene at 298 K.

Answer 1

In this polymerization reaction, every molecule of ethylene involves breaking of one C = C (double bond) and formed two C-C (single bonds). 

The amount of energy which is required to break one mole of

 

= 590 KJ

Thus, energy released in the formation of two moles of C-C single bond = 2 x 331 = 662 kJ 

Net energy released per mole of ethylene = 662- 590 = 72 kJ 

Enthalpy of polymerisation per mole of ethylene at 298 K (ΔH)= -72 kJ/mol.