Reaction Mechanisms without unknown rate-determining step

[JeremyPark14B]

If the problem gives a reaction mechanism, but doesn't state which is slow / fast, how can we determine the determining step rate law or overall rate reaction rate law?

[Matthew Tran 1H]

It's very unlikely that we would have to figure this out for ourselves as we've always been given which steps are fast and which step is slow. I suppose one way you could think about which step is slow is by looking at the molecularity. If the molecularity is high, we would expect the rate constant to be smaller since A (the frequency factor) would be smaller. E.g. termolecular elementary rxn would be expected to be slower than a unimolecular elementary rxn.

[Chem_Mod]

If a mechanism is provided, but there isn't enough information given to figure out which step is slow and which step(s) are fast, then there isn't enough information to be able to solve for the rate law of this reaction mechanism.

Hope this helps! :)