Chemical Kinetics - Result Question 32
32. In a first order reaction the concentration of reactant decreases from $800 $ $mol / dm^{3}$ to $50 $ $mol / dm^{3}$ in $2 \times 10^{4} $ $s$. The rate constant of reaction in $s^{-1}$ is
(a) $2 \times 10^{4}$
(b) $3.45 \times 10^{-5}$
(c) $1.386 \times 10^{-4}$
(d) $2 \times 10^{-4}$
$(2003,1 M)$
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Answer:
Correct Answer: 32. (c)
Solution:
- For a first order reaction, $k t=\ln \dfrac{[A] _0}{[A]}$
$ \begin{aligned} \Rightarrow \quad k=\dfrac{1}{t} \ln \dfrac{[A] _0}{[A]} & =\dfrac{1}{2 \times 10^{4}} \ln \dfrac{800}{50}=\dfrac{4 \ln 2}{2 \times 10^{4}} s^{-1} \\ = \quad 1.386 \times 10^{-4} s^{-1} \end{aligned} $
BETA
