Pre-Equilibrium Approach

[KarenaKaing_1D]

Can someone explain to me what step 2 is in the approach after treating the first step as equilibrium?

[Shrita Pendekanti 4B]

The objective of step 2 is to write the rate law of the rate-determining step (slow step) in a manner that agrees with the experimentally derived rate law. To do this, you must substitute the intermediate with something else that's present in the experimental rate law. So, you're substituting the intermediate [N2O2] with K[NO]^2, the relationship found in step 1, to get 2k[NO]^2[O2].

Hope this helps!