Question

Enthalpy of polymerisation of ethylene, as represented by the reaction, nCH2=CH2$\longrightarrow$ (-CH2-CH2-)n is -100 kJ per mole of ethylene. Given bond enthalpy of C=C bond is 600 kJ mol-1, enthalpy of C-C bond (in kJ mol) will be :

• A. 116.7
• B. 350
• C. 700
• D. Indeterminate

Answer 1

Answer: (B)

350

Answer 2

nCH2 = CH2 $\longrightarrow$ (– CH2 – CH2 –)n $\Delta$H = – 100 KJ/mole

Double bond of ethylene converted to two single bonds.

$\Delta$H = – 100 = B.E.C=C – 2 B.E.C–C

$\Rightarrow$– 100 = 600 – 2 ´ B.E.C–C $\Rightarrow$B.E.C–C = 350 KJ/mole