AFMC AFMC Solved Paper-2009

  • question_answer
    In the presence of a catalyst, activation energy of a reaction is lowered by 2 kcal at \[27{{\,}^{o}}C.\] Hence, rate will be

    A) 20 times                              

    B) 28 times

    C) 14 times                              

    D) remain the same

    Correct Answer: B

    Solution :

    Arrhenius equation is \[k=A{{e}^{-{{E}_{a}}/RT}}\]In the presence of catalyst, rate constant, \[k'=A{{e}^{-{{E}_{a}}'/RT}}\] Eq (ii) / Eq (i), we get \[\frac{k'}{k}={{e}^{({{E}_{a}}-E_{a}^{'})/RT}}\] \[\Rightarrow \]    \[\frac{k'}{k}={{e}^{\left( \frac{2000}{2\times 300} \right)}}={{e}^{3.33}}\] [\[\because \]\[{{E}_{a}}-{{E}_{a'}}=2000\,\,\text{cal}\](given)] On taking log both sides, \[\log \frac{k'}{k}=\frac{3.33}{2.303}\] \[\frac{k'}{k}=\text{antilog}\,\text{1}\text{.446}\,\,\text{=}\,\text{27}\text{.92}\approx 28\] We know that, rate \[(R)\propto k\] \[\therefore \] \[\frac{R'}{R}=\frac{k'}{k}=28\] or            \[R'=28\,R\]


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