Question

What is the half life of a radioactive substance 87.5% of any given amount of the substance disintegrate in 40 minutes?

Answer 1

1st Order Reaction

$k=\frac{2.303}{t}log\frac{\left[100\right]}{[100-x]}$

$k=\frac{2.303}{40}log\frac{\left[100\right]}{\left[12.5\right]}$

$k=5.2\times {10}^{-2}{min}^{-1}$

Half Life = $\frac{0.693}{k}$ = $\frac{0.693}{5.2\times {10}^{-2}}$ = 13.3 min