The second order reaction A → Products takes 13.5 s for the concentration of A to decrease from 0.740 M to 0.205 M. What is the value of k for this reaction?

Answer 1

A ==> P

Since it is 2nd order in A, we can write the rate equation as ...

Rate = k[A]²

The rate can be determined by the change in [A] with respect to time as ...

change in [A] = 0.740 M - 0.205 M = 0.535 M

change in time = 13.5 s

Rate = 0.535 M/13.5 s = 0.0396 M/s

From the rate equation we have:

0.0396 M/s = k[0.740]²

0.0396 M/s = k x 0.5476 M²

k = 0.0396 M/s / 0.5476 M²

k = 0.0723 M^-1s^-1 (Note the units of k for a 2nd order reaction)