BHU PMT BHU PMT (Screening) Solved Paper-2010

  • question_answer
    For a reaction\[A+2B\xrightarrow{{}}C+D\]the following data were obtain:
    Expt. Initial concentration \[(mol\,{{L}^{-1}})\] Initial rate of formation of D \[(mol\,{{L}^{-1}}{{\min }^{-1}})\]
    [A] [B]
    1. 0.1 0.1 \[6.0\times {{10}^{-3}}\]
    2. 0.3 0.2 \[7.2\times {{10}^{-2}}\]
    3. 0.3 0.1 \[2.88\times {{10}^{-1}}\]
    4. 0.4 0.1 \[2.4\times {{10}^{-2}}\]
    The correct rate law expression will be

    A)  \[Rate=k[A][B]\]

    B)  \[Rate=k[A]{{[B]}^{2}}\]

    C)  \[Rate=k{{[A]}^{2}}{{[B]}^{2}}\]

    D)  \[Rate=k{{[A]}^{2}}[B]\]

    Correct Answer: B

    Solution :

                     Let the order of reaction with respect to A is\[x\] and B is y. \[Rate=k{{[A]}^{x}}{{[B]}^{y}}\] 1.\[Rate=6.0\times {{10}^{-3}}={{(0.1)}^{x}}{{(0.1)}^{y}}\]            ...(i) 2. \[7.2\times {{10}^{-2}}={{(0.3)}^{x}}{{(0.2)}^{y}}\]                   ...(ii) 3. \[2.88\times {{10}^{1}}={{(0.3)}^{x}}{{(0.4)}^{y}}\]                ...(iii) 4. \[2.4\times {{10}^{2}}={{(0.4)}^{x}}{{(0.1)}^{y}}\]                   ...(iv) On dividing Eq. (i) by (iv), we get                 \[\frac{6.0\times {{10}^{-3}}}{2.4\times {{10}^{-2}}}={{\left( \frac{0.1}{0.4} \right)}^{x}}{{\left( \frac{0.1}{0.1} \right)}^{y}}\] \[\therefore \]  \[x=1\] On dividing Eq. (ii) by (iii), we get                 \[\frac{7.2\times {{10}^{-2}}}{28.8\times {{10}^{-2}}}={{\left( \frac{0.3}{0.3} \right)}^{x}}{{\left( \frac{0.2}{0.4} \right)}^{y}}\] \[\frac{1}{4}={{\left( \frac{1}{2} \right)}^{y}}\] \[y=2\] Thus, the rate law is \[rate=k\text{  }\!\![\!\!\text{ A }\!\!]\!\!\text{   }\!\![\!\!\text{ B}{{\text{ }\!\!]\!\!\text{ }}^{2}}\]


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