Rate Law For A Chemical Reaction

As we discuss in the previous, a reaction is defined as; "The process in which a substance changes into a new substance by changing its physical and chemical properties is called a reaction". 
A chemical reaction essentially involves products and reactants. In addition, certain critical conditions are required for the chemical reaction to proceed until its completion. These conditions include proper temperature and pressure, ionic strength, etc. 
However, every chemical reaction can be explained using two terms: "Rate Of Reaction" & "Rate Constant". 

The rate of reaction describes the rate at which the reaction proceeds and rate constant quantifies the rate of a reaction. The rate law is a relation that relates the rate of a reaction with the reaction rate constant and the concentration of the reacting species. The rate of reaction can be defined in terms of the amount of the reactants consumed and products formed in a unit of time. Every chemical reaction proceeds at a different rate.

In this article, we will study about the 'Rate Law' of the reaction in detail. 
What is the Rate Law??
How to write rate law for different types of reactions??

What Do You Understand By Rate Law
What Is A Rate Law???
......."Rate laws or rate equations are mathematical expressions that describe the relationship between the rate of a chemical reaction and the concentration of it's reactants".....
A rate law is sometimes called as a 'Differential Rate Law'. 
Let's have a look on an example;
Consider a chemical reaction described by chemical equation,
aA  ＋ bB ........  ➞    Products
Here, A & B are reactants and a &b are stoichiometric coefficients 
The rate law for this reaction is written as;
➩ { r = k[A]ⁿ [B]ᵐ......... }
      -------------------(1)
Where, 
      [A],[B],..... represent the molar concentration 
                      of reactants
        k = represent a proportionality constant or
                   the rate constant             
            r = represent the rate of reaction 

Here, equation (1) is known as "Rate Law" for the above chemical reaction. Rate laws provide a mathematical description of how changes in the amount of a substance affect the rate of a chemical reaction.
The value of "n,m,...." may or may not be same as the stoichiometric coefficient "a,b,...." of the reacting species in a balanced chemical equation. Equal for elementary reactions and not equal to multiple reaction which takes place more than one elementary steps.

For Example

How to determine rate law???
The determination of the rate law or rate equation is usually a two step procedure; first the concentration dependency is found at fixed temperature and then the temperature dependency of the reaction rate constant is found, yielding the complete rate law or rate equation. 
Dependence of rate of reaction with concentration of reactants species is given by the rate law equation....



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