Question

A first order reaction takes $40$ minutes for $30\%$ decomposition. Calculate $t_{1/2}$ value $(\log 7=0.845)$.

Answer 1

$t=\frac{2.303}{k}log\frac{100}{100-x}$

$40=\frac{2.303}{k}log\frac{100}{100-30}$

$k=8.919\times {10}^{-3}$

$t_{1/2}=\frac{0.693}{k}$

$t_{1/2}=77.6minutes$