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WB JEE Medical WB JEE Medical Solved Paper-2009

  • question_answer
    The time taken for 10% completion of a first order reaction is 20 min. Then, for 19% completion, the reaction will take

    A)  40 min                                 

    B)  60 min

    C)  30 min                                 

    D)  50 min

    Correct Answer: A

    Solution :

                     When the reaction is 10% completed, \[k=\frac{2.303}{20}\log \frac{100}{100-10}\]                                      ?(i) When the reaction is 19% completed, \[k=\frac{2.303}{t}\log \frac{100}{100-19}\]                                         ?(ii) From Eq (i) and (ii), \[\Rightarrow \]               \[\frac{2.303}{20}\log \frac{100}{90}=\frac{2.303}{t}\log \frac{100}{81}\] \[\Rightarrow \]               \[\frac{1}{20}\times 0.04575=\frac{1}{t}\times 0.09151\] \[\therefore \]  \[t=40\,\min .\]


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