CET Karnataka Medical CET - Karnataka Medical Solved Paper-2012

  • question_answer
    For a reaction: \[A+B\xrightarrow{{}}\]Products, the rate of the reaction at various concentrations are given below:
    Expt  [A] [B] \[~rate(mol\text{ }d{{m}^{-3}}\text{ }{{s}^{-1}})\]
    1 0.2 0.2 2
    2 0.2 0.4 4
    3 0.6 04 36
    The rate law for the above reaction is                    ,

    A)  \[r=k{{[A]}^{2}}[B]\]

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

    C)  \[r=k{{[A]}^{3}}[B]\]

    D)  \[r=k{{[A]}^{2}}{{[B]}^{2}}\]           

    Correct Answer: A

    Solution :

    : \[A+B\xrightarrow{{}}Products\] Rate \[=k{{[A]}^{\alpha }}{{[B]}^{\beta }}\] From expt. No. 1         \[2=k{{[0.2]}^{\alpha }}{{[0.4]}^{\beta }}\]                       ...(1) From expt. No. 2 \[4=k{{[0.2]}^{\alpha }}{{[0.4]}^{\beta }}\]                          ...(2) dividing eq. (1) and (2) we get \[\frac{2}{4}=\frac{k}{k}\frac{{{[0.2]}^{\alpha }}{{[0.2]}^{\beta }}}{{{[0.2]}^{\alpha }}{{[0.4]}^{\beta }}}\] or \[\frac{1}{2}={{\left[ \frac{1}{2} \right]}^{\beta }}\]\[\Rightarrow \]\[\beta =1\] From expt. No. 3 \[36=k{{[0.6]}^{\alpha }}{{[0.4]}^{\beta }}\]                       ...(3) dividing eqn. (2) and (3) we get \[\frac{4}{36}=\frac{k{{[0.2]}^{\alpha }}{{[0.4]}^{\beta }}}{k{{[0.6]}^{\alpha }}{{[0.4]}^{\beta }}}\] or \[\frac{1}{9}={{\left[ \frac{1}{3} \right]}^{\alpha }}\]\[\Rightarrow \]\[\alpha =2\] \[\Rightarrow \] Rate law for the given reaction is \[r=k{{[A]}^{2}}{{[B]}^{1}}\]


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