Question

For a given reaction of first order, it takes 20 minutes for the concentration to drop from $1.0 mol litre^{-1}$ to $0.6\, mol\, litre^{-1}$. The time required for the concentration to drop from $0.6\, mol \,litre^{-1}$ to $0.36\, mol \,litre^{-1}$ will be

• A. more than 20 minutes
• B. less than 20 minutes
• C. equal to 20 minutes
• D. infinity

Answer 1

Answer: (C)

$\frac{2.303}{20}$ log $\frac{1.0}{1.0-0.6}=\frac{2.303}{t}$ log $\frac{0.6}{0.6-0.36}$
$\therefore or \frac{1}{20}$ log $2.5=\frac{1}{t}$ log $2.5$
$\therefore t=20$ minutes