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`.

Options

A. `-70 kJ`
B. `-72 kJ`
C. `72 kJ`
D. `-68 kJ`

Explanation

The polymerisation of ethane may be represented as
`nCH_(2) = CH_(2) rarr [CH_(2)-CH_(2)]_(n)`
one mole of `C=C` bind is decomposed and two moles of `C-C`bonds are foemed per mole of ethane.
`:. DeltaH = 590 - 2 xx 331 =- 27 kJ` per mol of ethylene