Question

Assuming the CV initial concentration is 1.2 x 10-5 M, calculate the time required for the concentration to decrease to 40% of the initial value.

Answer 1

Need more information for the problem. Atleast we should know which order of the reaction it is.

For time sake think its First order for which we need K rate constant.

For first order rate equation is ln(Ca/Cao) = -kt => ln(0.4 Cao /Cao) = - kt => - 0.9163 = - kt => t = 0.9163 / k

If you know the rate constant substitute in that you will get time required.

If it is not first order consider taking this n th order Ca ^(1-n) - Cao^(1-n) = (n-1) kt where n is order of the reaction, doesnt hold for first order.