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Thermodynamics

# The polymerization of ethylene to linear polyethylene is represented by the reaction  $nCH_2=CH_2 \rightarrow (CH_2-CH_2)_n$  where $n$ has a large integral value. Given that $\Delta H_{C=C}$ and $\Delta H_{C-C}$ at 298 K are 590 and 331 kJ/mol. Calculate the enthalpy of polymerization per mol of ethylene.

$\begin {array} {1 1} (A)\;72\: kJ/mol & \quad (B)\;259\: kJ/mol \\ (C)\;-72\: kJ/mol & \quad (D)\;-259 \: kJ/mol \end {array}$

$\Delta H (polymerization) = \Delta H_{C=C} - 2 \Delta H_{C-C} = 590 – 2(331) = -72\: kJ/mol$
Ans : (C)