# What is a rate determining step example?

Feb 19, 2017

A nice example is $\text{Cl} \left(g\right)$-catalyzed ozone destruction:

${\text{Cl"(g) + "O"_3(g) => "ClO"(g) + "O}}_{2} \left(g\right)$

${\text{O"_3(g) + "ClO"(g) => "Cl"(g) + 2"O}}_{2} \left(g\right)$

$\text{----------------------------------------------}$

$2 {\text{O"_3(g) -> 3"O}}_{2} \left(g\right)$

You can see that $\text{Cl} \left(g\right)$ gets consumed in step 1 and produced in step 2 of the reaction mechanism above.

That makes it a catalyst, which speeds up the reaction by changing the reaction pathway, decreasing the activation energy.

On the other hand, $\text{ClO} \left(g\right)$ is an intermediate, since it gets produced in the middle of the reaction and gets consumed by the time the reaction is over.

This first step

${\text{Cl"(g) + "O"_3(g) => "ClO"(g) + "O}}_{2} \left(g\right)$,

is slow, since ${\text{O}}_{3}$ is bent, and a triatomic molecule having to align itself properly for a collision makes for a difficult collision and thus the chances of a successful collision are low.

The slow step is rate-determining, or rate-limiting.

(The second step is not as slow because $\text{ClO} \left(g\right)$ is really reactive.)