Question

A first order reaction is 60% complete in 20 minutes. How long will the reaction take to be 84% complete?

• A. 76 mins
• B. 54 mins
• C. 68 mins
• D. 40 mins

Answer 1

The correct option is D 40 mins

If a reaction is 60% complete, 40% remains and if it is 84% complete, 16% remains.

For a first order reaction:
$k=\frac{2.303}{20}log\frac{100}{40}=\frac{2.303}{t}log\frac{100}{16}$