What are the units for the rate constant of a reaction with the rate law, Rate = k[A][B]?

Question

options;

s^-1

Ms^-1

m^-1S^-1

M^-2S^-1

sM^-1

Answer 1

The order of the rate law is the sum of the exponents. In this case since both [A] and [B] are raised to the first power, the order = 2. So for a second order reaction, the units for k (rate constant) are M^-1s^-1 or any units of reciprocal concentration reciprocal time.

This can be calculated as follows, using M as concentration and sec as time.

Rate = k[A][B]

M/sec = k [M][M]

k = M/sec / M²

k = M^-1s^-1