# Kinetics: Order of Reaction

I am confused as to how an order of a reactant (n or m) in the rate law can be negative. This means that increasing the concentration of a reactant would actually decrease its rate of disappearance. How does this make sense? Doesn't a higher concentration always allow for more collisions? Also, when the order is 0, this means that concentration has no effect on the rate of disappearance. How does this make sense chemically/at the atomic level?

• – Mithoron Mar 4 '15 at 0:02

Basically, you have a two-step reaction: $$\ce{A + B <=> C}$$ $$\ce{C <=> D\ (slow)}$$ Increasing concentration of $\ce{C}$ would decrease the rate of reaction.