Rate Law Problem

Question

A reaction has the following rate law:

rate=k[BrO3−][Br−][H+]2

What are the units for k, the rate constant?

Answer 1

The units for the rate constant, k, will depend on the "order" of the reaction. So, one needs to obtain that information. From rate = k[BrO₃^-][Br^-][H⁺]², we see the reaction is first order with respect to BrO3^- and Br^- and second order with respect to H⁺. Thus, the overall order would be 4^th order (very unusual).

Now fill in the units (I'll use M and seconds).

M/s = k (M)(M)(M²)

M/s = k M⁴

k = M^-3s^-1 or reciprocal concentration -reciprocal time