The order
of an experimental rate equation describes how the rate depends
on the power of the concentration terms. The rate of breakdown of
carbon14 is proportional to the first power of C14 concentration,
so the reaction is first order.
The hydrogeniodine reaction rate depends on the product of two
concentrations, so the reaction is second
order in overall concentration.
One also can focus on the individual
reactants, and say that the HI reaction is separately first order
in H_{2} and I_{2}
concentrations, since these each occur in the rate equation with
a firstpower dependence.
Example. The
decomposition of N_{2}0_{5}
vapor,
has been observed experimentally to follow
the rate law
What is the order of this reaction?

