NEET Chemistry NEET PYQ-Chemical Kinetics

  • question_answer
    For the reaction, \[{{N}_{2}}{{O}_{5}}(g)\xrightarrow[{}]{{}}2N{{O}_{2}}(g)+\frac{1}{2}{{O}_{2}}(g)\]the value of rate of disappearance of \[{{\text{N}}_{\text{2}}}{{\text{O}}_{\text{5}}}\] is given as \[6.25\times {{10}^{-3}}\]\[\text{mol}\,{{\text{L}}^{\text{-1}}}{{\text{s}}^{\text{-1}}}\]. The rate of formation of \[N{{O}_{2}}\] and \[{{O}_{2}}\] is given respectively as            [AIPMT (S) 2010]

    A) \[6.25\times {{10}^{-3}}mol\,{{L}^{-1}}{{s}^{-1}}\]and \[6.25\times {{10}^{-3}}mol\,{{L}^{-1}}{{s}^{-1}}\]

    B) \[1.25\times {{10}^{-2}}mol\,{{L}^{-1}}{{s}^{-1}}\]and\[3.125\times {{10}^{-3}}mol\,{{L}^{-1}}{{s}^{-1}}\]

    C) \[6.25\times {{10}^{-3}}mol\,{{L}^{-1}}{{s}^{-1}}\]and \[3.125\times {{10}^{-3}}mol\,{{L}^{-1}}{{s}^{-1}}\]

    D) \[1.25\times {{10}^{-3}}mol\,{{L}^{-1}}{{s}^{-1}}\]and \[6.25\times {{10}^{-3}}mol\,{{L}^{-1}}{{s}^{-1}}\]

    Correct Answer: C

    Solution :

    [c] Key Idea Rate of disappearance of reactant = rate of appearance of product
    \[\text{or-}\frac{\text{1}}{\begin{align}   & \text{stoichiometric}\,\text{coefficient} \\  & \text{of}\,\text{reactant} \\ \end{align}}\]\[\frac{d\text{ }\!\![\!\!\text{ reactant}]}{dt}\]
    \[\text{=}\,\text{+}\frac{\text{1}}{\begin{align}   & \text{stoichiometric} \\  & \text{coefficient}\,\text{of}\,\text{product} \\ \end{align}}\]\[\frac{\text{d }\!\![\!\!\text{ product }\!\!]\!\!\text{ }}{\text{dt}}\]
    For the reaction,
    \[{{N}_{2}}{{O}_{5}}(g)\xrightarrow[{}]{{}}2N{{O}_{2}}(g)+\frac{1}{2}{{O}_{2}}(g)\]
                \[\frac{-d[{{N}_{2}}{{O}_{5}}]}{dt}=+\frac{1}{2}\frac{d[N{{O}_{2}}]}{dt}\]
                \[=+\frac{2d[{{O}_{2}}]}{dt}\]
    \[\therefore \]      \[\frac{d[N{{O}_{2}}]}{dt}=-2\frac{d[{{N}_{2}}{{O}_{5}}]}{dt}\]
                \[\text{=}\,\text{2 }\!\!\times\!\!\text{ }\,\text{6}\text{.25 }\!\!\times\!\!\text{ 1}{{\text{0}}^{-3}}\text{mol}\,{{\text{L}}^{-1}}{{\text{s}}^{-1}}\]
                \[\text{=}\,12.\text{5 }\!\!\times\!\!\text{ 1}{{\text{0}}^{-3}}\text{mol}\,{{\text{L}}^{-1}}{{\text{s}}^{-1}}\]
                \[\text{=}\,1.\text{25 }\!\!\times\!\!\text{ 1}{{\text{0}}^{-2}}\text{mol}\,{{\text{L}}^{-1}}{{\text{s}}^{-1}}\]
                \[\frac{d[{{O}_{2}}]}{dt}=-\frac{d[{{N}_{2}}{{O}_{5}}]}{dt}\times \frac{1}{2}\]
                \[=\frac{6.25\times {{10}^{-3}}mol\,{{L}^{-1}}\,{{s}^{-1}}}{2}\]
                \[=3.125\times {{10}^{-3}}mol\,{{L}^{-1}}\,{{s}^{-1}}\]


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