NEET Chemistry NEET PYQ-Chemical Kinetics

  • question_answer
    Mechanism of a hypothetical reaction\[{{X}_{2}}+{{Y}_{2}}\to 2XY\] is given below:            [NEET-2017]
    (i) \[{{X}_{2}}\to X+X(fast)\]
    (ii) \[X+{{Y}_{2}}XY+Y(slow)\]
    (iii)\[X+Y\to XY(fast)\]
                The overall order of the reaction will be

    A)             1.5

    B) 1

    C)             2

    D) 0

    Correct Answer: A

    Solution :

    [a] The solution of this question is given by assuming step (i) to be reversible which is not given in question
                Overall rate = Rate of slowest step (ii)
                            \[=k[X][{{Y}_{2}}]\]                             …(1)
                K=rate constant of step (ii)
    Assuming step (i) to be reversible, its equilibrium constant,
    \[{{k}_{eq}}=\frac{{{[X]}^{2}}}{[{{X}_{2}}]}\Rightarrow [X]={{k}_{eq}}^{\frac{1}{2}}{{[{{X}_{2}}]}^{\frac{1}{2}}}\]                      …(2)
    Put (2) in (1)
    \[Rate=k{{k}_{eq}}^{\frac{1}{2}}{{[{{X}_{2}}]}^{\frac{1}{2}}}[{{Y}_{1}}]\]
    Overall order \[=\frac{1}{2}+1=\frac{3}{2}\]


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