The polymerisation of ethylene to linear polyethylene is represented by the reaction
`nCH_(2)=CH_(2)rarr(-CH_(2)-CH_(2)-)_(n)`
When `n` has a large integral value. Given theat the average enthalpies of bond dissociation for `C=C` and `C-C` at `298K`are `+590` and `+331kJ mol^(-1)` respectively, calculate the enthalpy of polymerisation per mole of ethylene at `298K`.

Explanation

Polymerisation of ethylene to linear polythylene is
`n(CH_(2) = CH_(2)) rarr (CH_(2) -CH_(2))_(n)`
Energy released = Energy due to formation of two single bonds
` =2 xx 331 = 662 kJ "mole"^(-1)` of ethylene.
`DeltaH_("polymerisation") = 590 - 662`
`=- 72 kJ mol^(-1)`