Question

A first order reaction takes $69.3$ minutes for $50\%$ completion. How much time (in minute) will be needed for $80\%$ completion?
[Given: log 5= 0.7, Enter the nearest integer value]

Answer 1

For $50\%$ completion time required $=69.3min$

$\therefore t1/2=69.min$

$K=\frac{0.693}{t1/2}=\frac{0.693}{69.3}={10}^{-2}mi{n}^{-1}$

For completion, $\frac{Co}{Ct}=\frac{100}{100-80}=\frac{100}{20}=\frac{10}{2}$

For first order reaction-

$Kt=2.303\log \frac{Co}{Ct}$

$\Rightarrow t=\frac{2.303}{{10}^{-2}}\log \frac{10}{2}=2.303\times {10}^2\log 5\approx 161minutes$
Ans-$161$