JEE Main & Advanced Chemistry Chemical Kinetics Question Bank Rate of a reaction

  • question_answer A first order reaction complete its 10% in 20 minutes then time required to complete its 19% is  [Kerala CET  2005]

    A)                 30 minutes         

    B)                 40 minutes

    C)                 50 minutes         

    D)                 38 minutes

    E)                 45 minutes

    Correct Answer: B

    Solution :

               In first phase, \[K=\frac{2.303}{20}\log \frac{90}{100}\]     .....(i)                    In second phase \[K=\frac{2.303}{t}\log \frac{81}{100}\] .....(ii)                    From eq. (i) \[\frac{2.303}{20}\log \frac{90}{100}=\frac{2.303}{t}\log \frac{81}{100}\]                    \[t=\frac{20(\log 81-\log 100)}{(\log 90-\log 100)}\]                                 \[=\frac{20(1.908-2)}{(1.954-2)}=\frac{20\times (-0.092)}{(-0.046)}\]= 40 minutes

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