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NEET 2025
Exam
NEET
Year
2025
Subject
Chemistry
Chapter
Chemical Kinetics

NEET 2025 · Chemistry · Chemical Kinetics

If the rate constant of a reaction is 0.03 ~s^ -1 , how much time...

If the rate constant of a reaction is 0.03 s−10.03 \mathrm{~s}^{-1}, how much time does it take for 7.2 mol L−17.2 \mathrm{~mol} \mathrm{~L}^{-1} concentration of the reactant to get reduced to 0.9 mol L−10.9 \mathrm{~mol} \mathrm{~L}^{-1} ? (Given :log⁡2=0.301: \log 2=0.301 )

Options

  1. A69.3 s
  2. B23.1 s
  3. C210 s
  4. D21.0 s

Correct answer

A. 69.3 s

Step-by-step solution

K=0.03 s−1 (First order reaction) A0=7.2 mol L−1 At=0.9 mol L−17.2→t1/23.6→t1/21.8→t1/20.9t=3t1/2=3×0.6930.03=69.3 s\begin{aligned} & \mathrm{K}=0.03 \mathrm{~s}^{-1} \text{ (First order reaction) } \\ & \mathrm{A}_0=7.2 \mathrm{~mol} \mathrm{~L}^{-1} \\ & \mathrm{~A}_{\mathrm{t}}=0.9 \mathrm{~mol} \mathrm{~L}^{-1} \\ & 7.2 \xrightarrow{\mathrm{t}_{1/2}} 3.6 \xrightarrow{\mathrm{t}_{1/2}} 1.8 \xrightarrow{\mathrm{t}_{1/2}} 0.9 \\ & \mathrm{t}=3 \mathrm{t}_{1/2}=\frac{3 \times 0.693}{0.03}=69.3 \mathrm{~s}\end{aligned}
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