Chhattisgarh PMT Chhattisgarh PMT Solved Paper-2005

  • question_answer
    For the first order reaction with the constant k, which expression gives the half-life period? (Initial concentration = a)

    A)  \[\frac{\ln \,2}{k}\]                        

    B)  \[\frac{1}{k\times a}\]

    C)  \[\frac{0.693}{k\times a}\]                         

    D)  \[\frac{3}{2k{{a}^{2}}}\]

    Correct Answer: A

    Solution :

    From the first order reaction \[k=\frac{{{\log }_{n}}}{t}\left( \frac{a}{a-x} \right)\] \[k=\frac{{{\log }_{n}}}{{{t}_{1/2}}}\left( \frac{a}{a-\frac{a}{2}} \right)\]                 \[\because \]\[x=\frac{a}{2},\]                 \[t={{t}_{1/2}}\]                                 \[k=\frac{{{\log }_{n}}}{{{t}_{1/2}}}\frac{2a}{a},\] \[k=\frac{{{\log }_{n}}2}{{{t}_{1/2}}}\]                 or            \[{{t}_{1/2}}=\frac{{{\log }_{n}}2}{k}\]


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