CET Karnataka Engineering CET - Karnataka Engineering Solved Paper-2003

  • question_answer
    For a reaction \[A+B\xrightarrow{{}}C+D\], if concentration of A is doubled without altering that of B, rate doubles. If concentration of B is increased nine times without altering that of A, rate triples. Order of the reaction is :

    A)  2                                            

    B)  1

    C)  \[1\frac{1}{2}\]                               

    D)  \[1\frac{1}{3}\]

    Correct Answer: C

    Solution :

    Suppose, the rate of reaction depends upon \[x\] power of concentration of A and y power of concentration of B. Hence,                 \[{{r}_{1}}=k\,.{{[A]}^{x}}\]                 \[{{r}_{2}}=k\,.{{[2A]}^{x}}\] \[\therefore \]  \[\frac{{{r}_{1}}}{{{r}_{2}}}=\frac{{{[A]}^{x}}}{{{[2A]}^{x}}}=\frac{1}{2}\] \[\therefore \]  \[x=1\] Similarly,              \[{{r}_{1}}=k{{[B]}^{y}}\]                                 \[{{r}_{2}}=k{{[9B]}^{y}}\] \[\therefore \]                  \[\frac{{{r}_{1}}}{{{r}_{2}}}=\frac{{{[B]}^{y}}}{{{[9B]}^{y}}}=\frac{1}{3}\] \[\therefore \]                  \[{{\left( \frac{1}{3} \right)}^{2y}}=\frac{1}{3}\] or                            \[y=\frac{1}{2}\] Hence, correct rate-law for the reaction                 \[=k[A]\,{{[B]}^{1/2}}\] Hence, order of reaction \[=1+\frac{1}{2}=1\frac{1}{2}\]


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