KVPY Sample Paper KVPY Stream-SX Model Paper-29

  • question_answer
    The rate constant for the decomposition of a certain substance is \[2.80\times {{10}^{-3}}{{M}^{-1}}{{s}^{-1}}\]at \[30{}^\circ C\]and \[1.38\times {{10}^{-2}}{{M}^{-1}}{{s}^{-1}}\] at \[50{}^\circ C.\] The Arrhenius parameters [A] of the reaction is: \[(R= 8.314 \times {{10}^{-3}}kJmo{{l}^{-1}}{{K}^{-1}}).\]

    A) \[8.68\times {{10}^{8}}{{\operatorname{M}}^{-1}}{{\operatorname{s}}^{-1}}\]

    B) \[2.16\times {{10}^{7}}{{\operatorname{M}}^{-1}}{{\operatorname{s}}^{-1}}\]

    C) \[4.34\times {{10}^{8}}{{\operatorname{M}}^{-1}}{{\operatorname{s}}^{-1}}\]

    D) \[3.34\times {{10}^{8}}{{\operatorname{M}}^{-1}}{{\operatorname{s}}^{-1}}\]

    Correct Answer: C

    Solution :

    E and A can be evaluated using Arrhenius equation, since energy of activation \[{{E}_{a}}\] and pre-exponential factor, A are Arrhenius parameters. given rate constant
    \[{{k}_{1}},=2.80\times {{10}^{-3}}{{M}^{-1}}{{s}^{-1}}at30{}^\circ C(303K)\]
    \[{{k}_{2}}=1.38\times {{10}^{-2}}{{M}^{-1}}{{s}^{-1}}at50{}^\circ C(323K)\] 
    \[{{E}_{a}}=\frac{2.303R{{T}_{1}}{{T}_{2}}}{\left( {{T}_{1}}-{{T}_{2}} \right)}{{\log }_{10}}\frac{{{k}_{2}}}{{{k}_{1}}}\]
    \[=\frac{2.303\times 8.314\times {{10}^{-3}}\times 303\times 323}{\left( 323-303 \right)}{{\log }_{10}}\]
    \[\left( \frac{1.38\times {{10}^{-2}}}{2.80\times {{10}^{-3}}} \right)\]
    \[{{E}_{a}}=64.91kJ\,mo{{l}^{-1}}\]
    also \[k=A.{{e}^{-{{E}_{a}}/RT}}\]
    \[\therefore \]      \[A=K.{{e}^{-{{E}_{a}}/RT}}\]
    \[\operatorname{A}=2.80\times 1{{0}^{-3}}{{e}^{64}}{{^{.91}}^{/(8.314\times {{10}^{-3}}\times 303)}}\]
    \[=4.34\times {{10}^{8}}{{M}^{-1}}{{s}^{-1}}\]


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