Question

In a first order reaction, the concentration of the reactant decreases from 0.6 M to 0.3 M in 15 minutes. The time taken for the concentration to change from 0.1 M to 0.025 M in minutes is:

• A. 1.2
• B. 12
• C. 30
• D. 3

Answer 1

Answer: (C)

30

In a first-order reaction, the concentration of the reactant decreases from $0.6M$ to $0.3M$ in $15$ minutes. Since the concentration is reduced to one half, the half-life period is $15$ minutes.

The concentration changes from $0.1M$ to $0.025M$. Hence, the concentration reduces to one-fourth of the original concentration. The time taken for the concentration to change from $0.1M$ to $0.025M$ in minutes is equal to two half-life periods or $2\times 15=30$ minutes.

Hence, option $C$ is correct.