The following are the rate constants of two different reactions. What is the overall order of reaction for each?
$(a)$ $2.418 \times 10^{-5} \ hr^{-1}$
$(b)$ $7.1 \times 10^{-4} \ atm \ s^{-1}$

(A) The order of a reaction can be determined from the units of the rate constant $(k)$.
For a reaction of order $n$,the units of the rate constant are $(concentration)^{1-n} \ time^{-1}$.
$(a)$ The unit is $hr^{-1}$,which corresponds to $time^{-1}$. This implies $1-n = 0$,so $n = 1$. Thus,it is a $1^{st}$ order reaction.
$(b)$ The unit is $atm \ s^{-1}$,which corresponds to $(pressure)^1 \ time^{-1}$. This implies $1-n = 1$,so $n = 0$. Thus,it is a $0^{th}$ order reaction.