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Question: Answered & Verified by Expert
Calculate the rate constant of the first order reaction if $80 \%$ of the reactant decomposes in 60 minutes.
ChemistryChemical KineticsMHT CETMHT CET 2023 (14 May Shift 2)
Options:
  • A $2.68 \times 10^{-2}$ minute $^{-1}$
  • B $5.36 \times 10^{-2}$ minute $^{-1}$
  • C $1.34 \times 10^{-2}$ minute $^{-1}$
  • D $8.1 \times 10^{-2}$ minute $^{-1}$
Solution:
2816 Upvotes Verified Answer
The correct answer is: $2.68 \times 10^{-2}$ minute $^{-1}$
$\begin{aligned} \mathrm{k} & =\frac{2.303}{\mathrm{t}} \log _{10} \frac{[\mathrm{A}]_0}{[\mathrm{~A}]_{\mathrm{t}}} \\ & =\frac{2.303}{60} \log _{10} \frac{(100)}{(20)}=\frac{2.303}{60} \log _{10} \frac{10}{2} \\ & =\frac{2.303}{60}\left[\log _{10}(10)-\log _{10}(2)\right] \\ & =\frac{2.303}{60} \times 0.699=2.68 \times 10^{-2} \text { minute }^{-1}\end{aligned}$

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