Question

The half life period of a first order reaction is $10$ minutes. The time required for the concentration of the reactant to change from $0.08$ $M$ to $0.02$ $M$ is:

• A. $10min$
• B. $20min$
• C. $30min$
• D. $40min$

Answer 1

The correct option is B $20min$

$k=0.693/t_{1/2}=\frac{0.693}{10}=0.0693{min}^{-1}\therefore \ln \left(\frac{0.08}{0.02}\right)=kt$

$t=\frac{\ln \left(4\right)}{k}=\frac{\ln \left(4\right)}{0.0693}min=20min$