Question

What is a rate determining step example?

Answer 1

A nice example is `"Cl"(g)`-catalyzed ozone destruction:

`"Cl"(g) + "O"_3(g) => "ClO"(g) + "O"_2(g)`

`"O"_3(g) + "ClO"(g) => "Cl"(g) + 2"O"_2(g)`

`"----------------------------------------------"`

`2"O"_3(g) -> 3"O"_2(g)`

You can see that `"Cl"(g)` 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, `"ClO"(g)` 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

`"Cl"(g) + "O"_3(g) => "ClO"(g) + "O"_2(g)`,

is slow, since `"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.

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(The second step is not as slow because `"ClO"(g)` is really reactive.)