Equilibrium means "equal". In a chemical system, changes occur in substances called the reactants to produce another substance called the products. These changes from reactants to products and vice versa occur at an uneven rate until EQUILIBRIUM is reached.
In other words, equilibrium is attained when the reactants and products are formed at an equal or constant rate i.e. There is no net change to the system. For example, in the chemical system below:
A + B ⇌ C + D
This system is said to be at "EQUILIBRIUM" if the rate of reaction of the reactants (A and B) is equal to that of the products (C and D). That is, there is no net change (difference) in the reaction rate.
