Question

The time elapsed of a certain between 33% and 67% completion of a first order reaction is 30 minutes. What is the time needed for 25% completion?

• A. $150.5$ minutes
• B. $12.5$ minutes
• C. $180.5$ minutes
• D. $165.5$ minutes

Answer 1

The correct option is B $12.5$ minutes

$30=\frac{2.303}{k}log\frac{100}{33}-\frac{2.303}{k}log\frac{100}{67}$

$k=0.0236{min}^{-1}$

$0.0236=\frac{2.303}{t}log\frac{100}{75}$

$t=12.5minutes$