Question

The bond energies of $C=C$ and $C-C$ at $298K$ are $590$ and $331$ $kJ{mol}^{-1}$ respectively. The enthalpy of polymerisation per mole of ethylene is:

• A. $-70kJ$
• B. $-72kJ$
• C. $72kJ$
• D. $-68kJ$

Answer 1

The correct option is B $-72kJ$

The polymerisation of ethene has one mole of $C=C$ bond is decomposed and two moles of $C-C$ bonds are formed per mole of ethylene
$\therefore$ $\Delta H=590-2\times 331=-72kJ$ per mole of ethylene.