Why are catalysts so effective in small amounts?
By definition, catalysts serve to accelerate certain chemical reactions, by lowering the activation energy required for them to proceed. They are not consumed by the reaction, which is why they are effective in small amounts.
Catalysts don't get used up in reactions. Because of this, a single catalyst molecule can function again and again. Some catalysts are better than others for a given reaction. More effective catalysts reduce the time taken for 1/ the rate of travel of the molecule to the active site, 2/ the time the reaction takes, or 3/ the time it takes for products to diffuse away, or 4/ a combination of the above. The more effective a catalyst is in these factors, the less is needed to make it equally effective.
