Question

In first order reaction, the concentration of reactant decreases from $800\, mol\, cm ^{-3}$ to $50\, mol/ dm ^{-3}$ in $2 \times 10^{4} s$. The rate constant is

• A. $ 2\times 10^{4}s^{-1}$
• B. $3.45 \times 10^{-5} s^{-1}$
• C. $1.386 \times 10^{-4} s ^{-1}$
• D. $2 \times 10^{-4} s^{-1}$

Answer 1

Answer: (C)

For first order reaction, Rate constant,
$k=\frac{2.303}{t} \log \frac{a}{a-x}$
$\Rightarrow k=\frac{2.303}{2 \times 10^{4}} \log \frac{800}{50}$
$=1.386 \times 10^{-4} s^{-1}$