Dependence of Reaction on Catalyst Concentration

[Chem_Mod]

I understand that a heterogenous catalyst must attach themselves to the surface of a catalyst, however, what does this sentence mean: "the conc of the reactants is usually much greater than the number of active sites available on the catalyst so that the rate is determined by the surface area of the catalyst and not by the conc of pressures of the reactants." (does this have to do with adsorption?)

[Chem_Mod]

This analogy may be off the wall but let's try it anyway: think of having 700 outfits but only 10 hangers, "the amount of your outfits (analogous to the concentration of reactants) is much greater than the number of hangers (analogous to active sites of the catalyst). Hence, the rate that you can hang your close is limited by the # of hangers you have and is INDEPENDENT of the amount of outfits you have (therefore ZERO ORDER is not dependent on the concentration of reactants).

[Nico Medina]

I was wondering this too, thanks for the help!