Order of Reaction
The power to which the concentration of a given reactant is raised in the experimentally determined rate law.
Formula / equation
rate ∝ [A]^m
Unit
Dimensionless
In depth
Order is determined experimentally and may be zero, fractional or even negative — none of which is possible for a stoichiometric coefficient. A zero order means the rate is independent of that species, which typically happens when a surface or an enzyme is already saturated with it.
Examples in the real world
The decomposition of ammonia on hot platinum is zero order because the metal surface is fully covered.