Rates of Reaction #2: The Rate Law

The rate law for any chemical reaction is:

r=k[A]^x[B]^y

where:

•  k is the rate constant, dependent on the temperature, surface area, etc.
• [A] and [B] are the concentrations of the reactants
• x and y are values determined by experiments.

Order of reaction: sum of the rate law exponents

Half Life:
For some radioactive decay, the concentration of a substance is halved consistently after a certain duration of time. For example, some radioactive material's concentration may be halved every four hours.

The time that it takes for such a substance to decrease by half is called half life, or t_{½ .} And interestingly, this can be used to determine the rate constant:

k=ln(2) ÷ t_½