Question

A first order reaction is 75% completed in 72 min. How long time will it take for
(i) 50% completion (ii) 87.5% completion

Answer 1

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

$k=\frac{2.303}{72}log\frac{100}{25}$

$k=0.019{min}^{-1}$

(i) $t=\frac{2.303}{0.019}log\frac{100}{50}$

$t=36min$

(ii) $t=\frac{2.303}{0.019}log\frac{100}{12.5}$

$t=109.4min$