Determining the rate law from a mechanism with an initial slow step: Ozone reacts with nitrogen dioxide to produce oxygen and dinitrogen pentoxide
`O_(3)(g)+2NO_(2)(g)rarrO_(2)(g)+N_(2)O_(5)(g)`
The proposed mechanism is
`O_(3)(g)+NO_(2)(g)overset(slow)rarr NO_(3)(g)+O_(2)(g)`
`NO_(3)(g)+NO_(2)(g)overset("fast")rarrN_(2)O_(5)(g)`
What is the rate law predicted by this mechanism ?
Strategy : The designations "slow" and "fast" indicate the relative rates of the steps. The rate is determined completely by the slow step, or rate-determining sterp.

Explanation

The first step in the mechanism is rate determining because its rate is much slower than the second step. We can write the rate law directly from this step.
`Rate = k[O_(3)][NO_(2)]`