1. Tardigrade
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  3. Chemistry
  4. Rate constant of a first order reaction is 0.0693 min -1 . If we start with 20 mol L-1, it is reduced to 2.5 mol L-1 in:

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Q. Rate constant of a first order reaction is $ 0.0693\,\,{{\min }^{-1}} $ . If we start with $ 20\,mol\,{{L}^{-1}}, $ it is reduced to $ 2.5\,mol\,{{L}^{-1}} $ in:

JIPMERJIPMER 1997

Solution:

For, 1st order reaction, $ k=\frac{2.303}{t}=\log \frac{a}{(a-x)} $ Hence, $ t=\frac{2.303}{0.0693}\times \log \frac{20}{2.5} $ $ =\frac{2.303}{0.0693}\times \log \,{{(2)}^{3}} $ $ =\frac{2.303}{0.0693}\times 3\times 0.3010=30\min $