Question

A first order reaction requires 30 minutes for 50% completion. The time required to complete the reaction by 75% will be.

• A. 45 minutes
• B. 15 minutes
• C. 60 minutes
• D. None of these

Answer 1

Answer: (C)

60 minutes

Answer 2

$k = \frac{0.693}{30} = 0.0231$ ; $t = \frac{2.303}{k}\log\left( \frac{100}{100 - 75} \right)$

$t = \frac{2.303}{0.0231}\log 4 = 60\text{minutes}$