NEET AIPMT SOLVED PAPER SCREENING 2009

  • question_answer
    For the reaction, \[RX+Mg\xrightarrow[{}]{{}}RMgX\]products, it is observed that  (1) On doubling the initial concentration of A only, the rate of reaction is also doubled and. (2) On doubling the initial concentrations of both A and B, there is a change by a factor of 8 in the rate of the reaction. The rate of this reaction is, given by

    A) rate\[\text{mo}{{\text{l}}^{\text{-1}}}\]              

    B) rate\[\text{mo}{{\text{l}}^{\text{-1}}}\]

    C)                        rate\[\text{mo}{{\text{l}}^{\text{-1}}}\]

    D)        rate\[\text{mo}{{\text{l}}^{\text{-1}}}\]

    Correct Answer: B

    Solution :

    For the reaction, \[\underset{\begin{smallmatrix}  \text{ }\!\!|\!\!\text{ } \\  \text{H} \end{smallmatrix}}{\overset{\begin{smallmatrix}  \text{H} \\  \text{ }\!\!|\!\!\text{ } \end{smallmatrix}}{\mathop{\text{C}}}}\,=\underset{\begin{smallmatrix}  \text{ }\!\!|\!\!\text{ } \\  \text{H} \end{smallmatrix}}{\overset{\begin{smallmatrix}  \text{H} \\  \text{ }\!\!|\!\!\text{ } \end{smallmatrix}}{\mathop{\text{C}}}}\,+\text{H}-\xrightarrow[{}]{{}}\text{H}-\underset{\begin{smallmatrix}  \text{ }\!\!|\!\!\text{ } \\  \text{H} \end{smallmatrix}}{\overset{\begin{smallmatrix}  \text{H} \\  \text{ }\!\!|\!\!\text{ } \end{smallmatrix}}{\mathop{\text{C}}}}\,-\underset{\begin{smallmatrix}  \text{ }\!\!|\!\!\text{ } \\  \text{H} \end{smallmatrix}}{\overset{\begin{smallmatrix}  \text{H} \\  \text{ }\!\!|\!\!\text{ } \end{smallmatrix}}{\mathop{\text{C}}}}\,-\text{H}\]Products On doubling the initial concentration of A only, the rate of reaction is also doubled, therefore Rat\[\text{mo}{{\text{l}}^{\text{-1}}}\]                                                                 ...(i) Let initially rate law is Rate\[\text{mo}{{\text{l}}^{\text{-1}}}\]                                              ...(ii) If concentration of A and B both are doubled, the rate gets changed by a factor of 8. \[\text{mo}{{\text{l}}^{\text{-1}}}\]                                       ?(iii) \[\text{mo}{{\text{l}}^{\text{-1}}}\] Dividing Eq. (iii) by Eq. (ii), \[1.77\times {{10}^{-5}}\] \[5.65\times {{10}^{-10}}\] \[6.50\times {{10}^{-12}}\]\[5.65\times {{10}^{-13}}\] Hence, rate law is, rate\[5.65\times {{10}^{-12}}\]


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