ThermochemistryHard
Question
The polymerization of ethylene to linear polyethylene is represented by the reaction
nCH2 = CH2→ (−CH2−CH2−)n
where n has a large integral value. Given that the average enthalpies of bond dissociation for C=C and C−C at 298 K are +590 and +331 kJ/mol, respectively, the enthalpy of polymerization per mole of ethylene at 298 K is
Options
A.−72 kJ
B.+259 kJ
C.−259 kJ
D.−849 kJ
Solution
In such polymerization, one sigma bond is formed on cleavage of one pi bond.
$\Delta H_{\text{Required}} = \left( \text{B.E}\text{.}_{C - C\pi\text{ bond}} \right) - \left( \text{B.E}\text{.}_{C - C\sigma\text{ bond}} \right) $$$ = (590 - 331) - (331) = - 72\text{ kJ/mol}$$
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