Question

A first order reaction is 20% complete in 10 minutes. Calculate the time taken for the reaction to go to 80% completion.

• A. 72.18 min
• B. 10.00 min
• C. 36.28 min
• D. 16.09 min

Answer 1

The correct option is A 72.18 min

Given t=10 min, If $a=100,x=20$ or $(a-x)=80$
Applying first order equation,
$k=\frac{2.303}{t}lo{g}_{10}\frac{100}{(100-20)}$
$=\frac{2.303}{10}lo{g}_{10}\frac{100}{80}=0.0223mi{n}^{-1}$

If $a=100,x=80$ or $(a-x)=20$
Again applying first order equation,
$t=\frac{2.303}{k}lo{g}_{10}\frac{100}{(100-80)}$
$=\frac{2.303}{0.0223}lo{g}_{10}\frac{100}{20}$
$=72.18min$