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

`nCH_(2)=CH_(2)to(-CH_(2)-CH_(2)-)_(n)`
there are equal number of C-H bonds on both sides but on reactant side there are nC=C bonds and on product side `(2n+1)C-C` bonds.
Enthalpy of polymerisation,
`=nDeltaH_((C=C))-(2n+1)DeltaH_((C-C))`
`=590n-(2n+1)(331)`
`=590n-662n` [2n+1`to2n` as n is very large]
`=72nkJ`
Enthalpy of polymerisation per mole
`=(DeltaH)/(n)=(72n)/(n)=72kJ" "mol^(-1)`.