Question

The rate constant for a first order reaction is $4.606 \times 10^{-3} s^{-1}$. The time required to reduce $2.0\,g$ of the reactant to $0.2\,g$ is :

• A. 100 s
• B. 200 s
• C. 500 s
• D. 1000 s

Answer 1

Answer: (C)

500 s

Answer 2

$K=\frac{2.303}{t}log\, \frac{a}{a-x}$ $t=\frac{2.303}{4.606\times 10^{-3}}$ $log\,\frac{2}{0.2}$ $=\frac{1000}{2} \,log\,10$ $=500\,sec$ (as log $10=1)$