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  4. The half life of a substance in a certain enzymecatalysed reaction is 138 s. The time required for the concentration of the substance to fall from 1.28 mg L-1 to 0.04 mg L-1, is -

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Q. The half life of a substance in a certain enzymecatalysed reaction is 138 s. The time required for the concentration of the substance to fall from $ 1.28 \, mg \, L^{-1} $ to $0.04 \, mg \, L^{-1}$, is -

AIPMTAIPMT 2011Chemical Kinetics

Solution:

1.28 → 0.64 → 0.32 → 0.16 → 0.08 → 0.04
No. of half lifes (n) = 5
$ 5 = \frac{Total \, times}{138}$
$= 5 \times 138$
time required $ = 690 \, s$