Chemical Thermodynamics Question 472
Question: The polymerization of ethylene to linear polyethylene is represented by the reaction $ nCH_2=CH_2\xrightarrow{,},{{(-CH_2-CH_2-)}_{n}} $ when ’n’ has a large integral value. Given that average enthalpies of bond dissociation for $ C=C $ and $ C-C $ at 298 K are + 590 and $ +331kJmo{{l}^{-1}} $ respectively. Then the enthalpy of polymerization/mol of ethylene at298 K is
Options:
A) - 132 kJ
B) - 72 kJ
C) + 80 kJ
D) + 162 kJ
Show Answer
Answer:
Correct Answer: B
Solution:
- $ n(CH_2=CH_2)\xrightarrow{\ },{{(-CH_2-CH_2-)}_{n}}, $
$ \Delta H=- $
Thus, ’n’ double bonds are dissociated to form a molecule with 2n single bonds. $ \Delta H=( \frac{n}{n} )({\Sigma_{C=C}})-( \frac{2n}{n} )({\Sigma_{C=C}}) $
$ =+,590-2\times 331=-72,kJ,mo{{l}^{-1}} $
