reaction mechanism

Drad

I experimentally determined the reaction rate of the following reaction:

4HCl(aq) + 4NaS2O3(aq) -> 4NaCl(aq) + 3S(s) + 5SO2(aq) + 2H2O(l)

and found that the rate was proportional to [NaS2O3]^1 and [HCl]^2

I know that it's probably too tricky to determine the reaction mechanism or rate determining step for this reaction. But I was wondering if someone could give me a simple example of how 2 reactants in equal proportions (e.g. 4HCl and 4NaS2O3) can affect the reaction rate differently from each other (e.g. []^1 and []^2) I would have thought they would both be ^1.

Drad

ok I just thought of this:

first step: A + B <-> AB
rate determining step: A + AB -> AAB
third step: B + AAB -> final products

I guess it's plausible as a simple example

Bystander

Good enough --- the temptation to interpret mechanism in terms of stoichiometry rather than measured rates is as tough to overcome as the temptation to relate reaction rates to free energies of reactions.