The chemical reaction which is expressed by using molecular formulae of reactants and products is called chemical equation. The chemical equation is also called formula equation.
The chemical equation in which the total number of atoms of each element in reactant and product is not equal is called an unbalanced chemical equation or skeletal chemical equation.
Skeletal chemical equation does not follow the law of conservation of mass.
Balanced chemical equation is a type of equation in which a total number of atoms in reactants and products are equal. It is based on the law of conservation of mass.
The chemical reaction that occurs only in one direction is called irreversible reaction.
The chemical reaction that occurs both in forward and backward directions is called reversible reaction.