Question

r =k[A] for a reaction, 50% of A is decomposed in 120 minutes. The time taken for 90% decomposition of A is ______ minutes.

Answer 1

For a first-order reaction:

$t_{1/2} = 120 \, \text{min}$

For 90% completion:

$t = \frac{2.303}{k} \log \left( \frac{a}{a - x} \right)$ $t = \frac{2.303 \times 120}{0.693} \log \left( \frac{100}{10} \right)$ $t = 399 \, \text{min}.$