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KVPY Sample Paper KVPY Stream-SX Model Paper-28

  • question_answer
    The decomposition of azo methane, at certain temperature according to the equation \[{{(C{{H}_{3}})}_{2}}{{N}_{2}}\to {{C}_{2}}{{H}_{6}}+{{N}_{2}}\] is a first order reaction. After 40 minutes from the start, the total pressure developed is found to be 350 mm Hg in place of initial pressure 200 mm Hg of azo methane. The value of rate constant k is -

    A) \[2.88\times {{10}^{-4}}se{{c}^{-1}}\]

    B) \[1.25\times {{10}^{-4}}se{{c}^{-1}}\]

    C) \[5.77\times {{10}^{-4}}se{{c}^{-1}}\]

    D) None of these

    Correct Answer: C

    Solution :

    \[k=\frac{2.303}{t}\log \left( \frac{{{P}_{i}}}{{{P}_{t}}} \right);(C{{H}_{3}}){{N}_{2}}\xrightarrow{{}}{{C}_{2}}{{H}_{6}}+{{N}_{2}}\]
                \[\begin{matrix}    t=0 & 200\,\,; & t & 200-x & x & x  \\ \end{matrix}\]
                as per given \[200+x=350\]         \[x=150\]
                \[\therefore \,\,\,k=\frac{2.303}{t}\log \left( \frac{200}{200-150} \right)\]
                \[k=5.77\times {{10}^{-\,4}}{{\sec }^{-\,1}}\]


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