The rate law is defined as the law which is used for studying the relationship between the rate of reaction and the concentration of the reactants. The rate law (also known as the rate equation) for a chemical reaction is an expression that provides a relationship between the rate of the reaction and the concentrations of the reactants participating in it.
Ways to determine rate law
Following are the ways to determine the rate law:
- Isolation method: In this method, the rate law is determined by considering the reactants in large quantities except for one.
For example, consider the following reaction:
A + B → C
Where [B] is taken in large quantity and is assumed that the concentration of b is constant, then the rate law becomes:
v = k’ [A]
k’ = k [B]0
The above equation is known as pseudo-first-order rate law. The isolation method helps to determine the dependence of the rate of the concentration of each reactant.
- Method of initial rate:
In this method, the reaction rate is measured for different concentrations of reactants at the beginning of the reaction.
log v = log k + a log [A]0
v0 is the initial rate and [A]0 is the initial concentration of A