KVPY Sample Paper KVPY Stream-SX Model Paper-18

  • question_answer
    The rate constant, the activation energy and the Arrhenius parameter of a chemical reaction at \[25{}^\circ C\] are \[3\times {{10}^{-4}}{{s}^{-1}},\] \[104.4\,\,kJ\,mo{{l}^{-1}}\] and \[6.0\times {{10}^{14}}{{s}^{-\,1}}\] respectively. The value of rate constant at \[T\to \infty \] is closest to

    A) \[2\times {{10}^{18}}{{s}^{-\,1}}\]

    B) \[6\times {{10}^{14}}{{s}^{-\,1}}\]

    C) \[3.6\times {{10}^{30}}{{s}^{-\,1}}\]

    D) infinity

    Correct Answer: B

    Solution :

    Given, \[{{T}_{1}}=25{}^\circ C=298K\,{{T}_{2}}=T\]
    \[{{E}_{a}}=104.4kJ\,mo{{l}^{-1}}=104.4\times {{10}^{3}}J\,mo{{l}^{-\,1}}\]
    \[{{k}_{1}}=3\times {{10}^{-\,4}}{{s}^{-\,1}},{{k}_{2}}=?\]
    According to Arrhenius equation \[\log \frac{{{k}_{2}}}{{{k}_{1}}}=\frac{{{E}_{a}}}{2.303R}\left[ \frac{1}{{{T}_{1}}}-\frac{1}{{{T}_{2}}} \right]\]
    \[\log \frac{{{k}_{2}}}{3\times {{10}^{-\,4}}}=\frac{104.4\times {{10}^{3}}}{2.303\times 8.314}\times \frac{1}{298}\]\[\left[ asT\to \infty ,\frac{1}{T}\to 0 \right]\]
    \[\log \frac{{{k}_{2}}}{3\times {{10}^{-4}}}=18.297\]
    \[\frac{{{k}_{2}}}{3\times {{10}^{-\,4}}}=1.98\times {{10}^{18}}\]
    \[{{k}_{2}}=1.98\times {{10}^{18}}\times 3\times {{10}^{-\,4}}\]\[=5.94\times {{10}^{4}}\approx 6\times {{10}^{14}}{{s}^{-\,1}}\]


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