Question

In a first order reaction, the concentration of reactant decreases from $400 \, mol$ $L^{-1}$ to $25 \, mol$ $L^{-1}$ in $200$ seconds. The rate constant for the reaction is

• A. $1.0386$ $s^{-1}$
• B. $2\times10^{-4}$ $s^{-1}$
• C. $1.386\times10^{-2}$ $s^{-1}$
• D. $3.4\times10^{-4}$ $s^{-1}$

Answer 1

Answer: (C)

For first order reaction,
$k=\frac{2.303}{t} log$ $ \frac{a}{\left(a-x\right)}=\frac{2.303}{200} log$ $\frac{400}{25}$
$=\frac{2.303}{200}\times1.204$ $=0.01386$ $s^{-1}$ $=1.386\times10^{-2}$ $s^{-1}$