The polymerisation of propene to linear polypropene is represented by the reaction
`n (overset (CH _(3)) overset(|) (CH) = CH _(2)) to (overset(CH_(3)) overset(|) (CH) - CH _(2) - ) n `
where n has large integral value, the average enthalpies of bond dissociation for(C=C) and(C-C) at 298K are +590 and `+331 kJ mol^(-1),` respectively. The enthalpy of polymerisation is `-360 kJ mol^(-1).` Find the value of n.

Explanation

Energy released = Energy due to formation of two single bonds ` = 2 xx 331 = 66 2 kJ mol ^(-1) `of proper `Delta H ` polymerisation/mol ` = 590 - 662 =-72 kJ mol ^(-1)`
`Delta H` polymerisation `= - 72 xx n =- 360 n = 5`