Question

The time taken for $10\%$ completion of a first order reaction is $20$ minutes. Then, for $19\%$ completion, the reaction will take:

• A. $40mins$
• B. $60mins$
• C. $30mins$
• D. $50mins$

Answer 1

Answer: (A)

$40mins$

In the first phase, $K=\frac{2.303}{20}\log \frac{100}{90}$ ...(i)

In the second phase, $K=\frac{2.303}{20}\log \frac{100}{81}$ ...(ii)

From eq. (i)$\frac{2.303}{20}\log \frac{100}{90}=\frac{2.303}{t}\log \frac{100}{81}$

$t=40mins$