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CET Karnataka Medical CET - Karnataka Medical Solved Paper-2000

  • question_answer
    A reaction that is of the first order with respect to reactant A has a rate constant \[6\text{ }mi{{n}^{-1}}\]. If we start with \[[A]=0.5\,mol\,{{L}^{-1}}\] when would [A] reach the value \[0.05mol\,{{L}^{-1}}\]?

    A)  \[0.384\text{ }min\]

    B)  \[0.15\text{ }min\]

    C)  \[3\text{ }min\]

    D)  \[3.84\text{ }min\]

    Correct Answer: A

    Solution :

    We know that for first order kinetics \[K=\frac{2.303}{t}\log \frac{a}{a-x}\] Here \[K=6{{\min }^{-1}},\,\,a=0.5\,mol\,{{L}^{-1}}\] \[(a-x)=0.05mol\,{{L}^{-1}}\] \[6=\frac{2.303}{t}\log \frac{0.5}{0.05}\] or \[t=\frac{2.303}{6}\log \frac{0.5}{0.05}=\frac{2.303}{6}=0.384\]


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