Units of rate constant of first and zero order reactions in terms of molarity M unit are respectively :

rate constant measurement unit $\mathrm{K}\text{ is }(\text{ Molarity }{)}^{1-1}{\text{ time }}^{-1}\text{. }$

In this case, n denotes the reaction's order.

n=1 for a first order reaction.

rate constant measurement unit $\mathrm{K}{\text{ is (Molarity) }}^{1-1}{\sec }^{-1}={\sec }^{-1}\text{. }$

n = 0 in a reaction of zero order.

rate constant measurement unit

$\mathrm{K}{\text{ is (Molarity) }}^{1-0}{\sec }^{-1}$=

$=\left(\text{ Molarity }\right){\sec }^{-1}$

$\left(\mathrm{M}\right) {\sec }^{-1}$