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NEET 2022
Exam
NEET
Year
2022
Subject
Chemistry
Chapter
Chemical Kinetics

NEET 2022 · Chemistry · Chemical Kinetics

The half life of a first order reaction is 2000 years. If the...

The half life of a first order reaction is 2000 years. If the concentration after 8000 years is 0.02M0.02 \mathrm{M}, then the initial concentration was :

Options

  1. A0.16M0.16 \mathrm{M}
  2. B0.32M0.32 \mathrm{M}
  3. C0.08M0.08 \mathrm{M}
  4. D0.04M0.04 \mathrm{M}

Correct answer

B. 0.32M0.32 \mathrm{M}

Step-by-step solution

Half life period (t1/2)=2000\left(t_{1/2}\right)=2000 years k=0.6932000k=2.303tlog⁡[A]o[ A]t0.6932000=2.3038000log⁡[A]o0.02∴[A]o=0.32M\begin{aligned} k & =\frac{0.693}{2000} \\ k & =\frac{2.303}{t} \log \frac{[\mathrm{A}]_o}{[\mathrm{~A}]_t} \\ \frac{0.693}{2000} & =\frac{2.303}{8000} \log \frac{[\mathrm{A}]_o}{0.02} \\ \therefore \quad[\mathrm{A}]_o & =0.32 \mathrm{M} \end{aligned}
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