Question

A second order reaction in which both the reactants have same concentration, is 20% completes in 500 seconds. How much time it will take for 60% completion?

• A. 300 seconds
• B. 500 seconds
• C. 5000 seconds
• D. 3000 seconds

Answer 1

The correct option is D 3000 seconds

The second order equation when both the reactants have same concentration is
$k=\frac{1}{t}.\frac{x}{a(a-x)}$
If a = 100, x = 20, t = 500 seconds.
So, $k=\frac{1}{500}\times \frac{20}{100\times (100-20)}$
When a = 100, x = 60, t = ?
$t=\frac{1}{k}.\frac{60}{100\times 40}$
Substituting the value of k,
$t=\frac{500\times 100\times 80}{20}\times \frac{60}{100\times 40}$
or t = 3000 seconds