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JEE Main & Advanced Chemistry Thermodynamics / रासायनिक उष्मागतिकी Sample Paper Topic Test - Thermo Chemistry (Thermodynamics)

  • question_answer
    The polymerization of ethylene to linear polyethylene is represented by the reaction \[nC{{H}_{2}}=C{{H}_{2}}\xrightarrow{\,}\,{{(-C{{H}_{2}}-C{{H}_{2}}-)}_{n}}\] 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 \[+331\,\,kJ\,\,mo{{l}^{-1}}\] respectively. Then the enthalpy of polymerization/mol of ethylene at298 K is

    A) - 132 kJ

    B) - 72 kJ

    C) + 80 kJ

    D) + 162 kJ

    Correct Answer: B

    Solution :

    [b] \[n(C{{H}_{2}}=C{{H}_{2}})\xrightarrow{\ }\,{{(-C{{H}_{2}}-C{{H}_{2}}-)}_{n}},\]
    \[\Delta H=?\]
    Thus, 'n' double bonds are dissociated to form a molecule with 2n single bonds.
    \[\Delta H=\left( \frac{n}{n} \right)({{\Sigma }_{C=C}})-\left( \frac{2n}{n} \right)({{\Sigma }_{C=C}})\]
    \[=+\,590-2\times 331=-72\,kJ\,mo{{l}^{-1}}\]


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