Question

In a first order reaction, the concentration of the reactant decreases from 0.8M to 0.4M in 15 min. The time taken for the concentration to change from 0.1 M to 0.025 M is:

• A. 60 min
• B. 15 min
• C. 7.5 min
• D. 30 min

Answer 1

The correct option is D 30 min

$k=\frac{2.303}{t}log\frac{\left[A\right]}{[A-x]}$

$k=\frac{2.303}{15}log\frac{0.8}{0.4}$

$k=0.046{min}^{-1}$

The time required

$0.046=\frac{2.303}{t}log\frac{0.1}{0.025}$

$t=30min$