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Question: Answered & Verified by Expert
In the first order reaction, $75 \%$ of the reactant gets disappeared in 1.386 hours. The rate constant of the reaction is
ChemistryChemical KineticsJIPMERJIPMER 2012
Options:
  • A $3.0 \times 10^{-3} \mathrm{~s}^{-1}$
  • B $2.8 \times 10^{-4} \mathrm{~s}^{-1}$
  • C $17.2 \times 10^{-3} \mathrm{~s}^{-1}$
  • D $1.8 \times 10^{-3} \mathrm{~s}^{-1}$
Solution:
1673 Upvotes Verified Answer
The correct answer is: $2.8 \times 10^{-4} \mathrm{~s}^{-1}$
For a first order reaction,
$k=\frac{2.303}{1.386 \times 60 \times 60} \log \frac{a}{a-0.75 a}$
$=\frac{2.303}{1.386 \times 60 \times 60} \log 4$
$=2.8 \times 10^{-4} \mathrm{~s}^{-1}$

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