Question

In `C_(2)H_(4)` energies of formation of `(C=C) and (C-C)` are -145 kJ/mol and -80kJ/mol respectively. What is the enthalpy change w hen ethylene polymerises to form polythene?
A. `+650kJ//mol`
B. `+65kJ//mol`
C. `-650kJ" "mol^(-1)`
D. `-65kJ" "mol^(-1)`

Answer 1

Correct Answer - B
Polymerisation of ethane may be given as:
`nCH_(2)=CH_(2)to(-CH_(2)-CH_(2)-)_(n)`
`DeltaH=sum(BE)_("reactants")-sum(BE)_("Products")`
`=(+145)-(+80)=+65kJ//mol`