KVPY Sample Paper KVPY Stream-SX Model Paper-26

  • question_answer
    The rate constant, the activation energy and the Arrhenius parameter of a chemical reaction at \[25{}^\circ C\] are \[3.0\times 1{{0}^{-4}}{{s}^{-1}},\]\[104.4{{\operatorname{kJmol}}^{-1}}\] 'and \[6.0\times 1{{0}^{14}}{{s}^{-1}}\]respectively. The value of the rate constant as\[\operatorname{T}\to \infty \] is

    A) \[2.0\times {{10}^{18}}{{\operatorname{s}}^{-1}}\]

    B) \[6.0\times {{10}^{14}}{{\operatorname{s}}^{-1}}\]

    C) Infinity

    D) \[3.6\times {{10}^{30}}{{\operatorname{s}}^{-1}}\]

    Correct Answer: B

    Solution :

    \[{{T}_{2}}=T(say),{{T}_{1}}=25{}^\circ C=298K,\]
    \[{{E}_{a}}=104.4kJmo{{l}^{-1}}=104.4\times {{10}^{3}}Jmo{{l}^{-1}}\]
    \[{{k}_{1}}=3\times {{10}^{-4}},{{k}_{2}}=?,\]
    \[\log \frac{{{k}_{2}}}{{{k}_{1}}}=\frac{{{E}_{a}}}{2.303R}\left[ \frac{1}{{{T}_{1}}}-\frac{1}{{{T}_{2}}} \right]\]
    \[\log \frac{{{k}_{2}}}{3\times {{10}^{-4}}}=\frac{104.4\times {{10}^{3}}J\,mo{{l}^{-1}}}{2.303\times (8.314J{{K}^{-1}}mo{{l}^{-1}})}\]    
    \[\left[ \frac{1}{298}-\frac{1}{\operatorname{T}} \right]\]
    As \[T\to \infty ,\frac{1}{T}\to 0\]
    \[\therefore \]\[\log \frac{{{k}_{2}}}{3\times {{10}^{-4}}}=\frac{104.4\times {{10}^{3}}J\,mo{{l}^{-1}}}{2.303\times 8.314\times 298}\]
    \[\log \frac{{{k}_{2}}}{3\times {{10}^{-4}}}=18.297,\frac{{{k}_{2}}}{3\times {{10}^{-4}}}=1.98\times {{10}^{18}}\]
    \[{{k}_{2}}=(1.98\times {{10}^{18}})\times (3\times {{10}^{-4}})=6\times {{10}^{14}}{{s}^{-1}}\]


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