A certain first-order reaction (A→products) has a rate constant of 9.00*10-3 s-1 at 45 ∘C. How many minutes does it take for the concentration of the reactant, [A], to drop to 6.25% of the original concentration?

27.8 minutes

Explanation:

The reaction follows a first order

Rate = k[A] = change in concentration/time

k = 9*10^-3s^-1

Let the original concentration of A be y

Concentration of A at time t = 6.25% * y = 0.0625y

Change in concentration = y - 0.0625y = 0.9375y

0.009 * 0.0625y = 0.9375y/t

t = 0.9375y/0.0005625y = 1666.7sec = 1666.7/60 = 27.8 minutes