A never-ending process which hold the universe. The chemical reaction in the sun, the nuclear fusion, generates energy and that’s how we sustain. The metabolic activities in living things, may it be digestion, respiration or even photosynthesis, it is an example for chemical reaction. Now you know the importance of chemical reaction, right?
Chemical reaction is the process in which the chemical bond between the molecules in a reactant is broken and new bonds are formed in molecules of the product in order to produce or form a new substance or compound.
Before getting deep into chemical reactions, we shall first discuss about physical and chemical changes.
During the physical change, the orientation of molecules is altered leading to state change of the substance. New products are not formed chemically, and the molecular composition remains exactly the same as that of the reactant or the substance which exhibited the physical change.  The molecular composition of ice and water is not altered while the change of state occurs, right?
The is no energy change as a result of a physical change. The energy required or spent to bring a physical change is absolutely equal to the value  of energy required to reverse the change which happened. So the energy is actually conserved. The physical changes are reversible and temporary. The reaction can be completely reversed if the cause of producing the change or the external work is removed. Water on freezing forms ice and ice on melting forms water, this is the most common and simple example for a physical change. The mass of the substance remains the same during the physical change. Energy is the only aspect related to a physical change as there is no involvement of mass in the physical change.
The chemical change is change of substance in which the molecular composition, arrangement or orientation is completely altered or modified and a completely new product with entirely different properties is formed. Chemical change results in creating a completely new and different  product. Chemical change occurring to a substance are irreversible and permanent. Thus it is evident that the reaction or change cannot be reversed, to create the reactants after an experiment. In chemical change, the mass of the substance is changed as it results in either the addition or removal of compounds or substances, in result, mass. There is a change in energy during the chemical change as there is an energy difference or enthalpy difference in the breaking old bonds in reactants and in  the formation of new bonds in products or resultant substances.
The energy released to the surroundings in the form of heat energy, if the energy required to break the bond in the product is higher than the energy required to make the bonds. These changes or reactions in which heat is released or dissipated are called exothermic.
But in some changes, the energy is used up from the surroundings or environment when the energy needed to break the bond is lower than the energy required for bonding the substances in the reactant. Such reactions in which heat is used up or absorbed from the surrounding or the environment are called endothermic reactions.
There are different types of chemical reactions based on the products formed, types of reactants involved in the reaction and many more. Some of them are
1. Combustion Reaction
In a combustion reaction, a combustible material reacts with an oxidizer to give an oxidized product. An oxidizer is a chemical a substance often referred to as a fuel required to burn, mostly  oxygen.
2. Decomposition Reaction
In a decomposition reaction, a single component or compound breaks down into two or multiple products. For this change to occur, heat, light or electricity comes into action.
3. Neutralization Reaction
The reaction between an acid and a base giving salt and water as the product is generally termed as a Neutralization reaction. The water molecule formed is by the combination of OH– ions and H+ ions. The resultant pH will be 7, hence the name neutralization.
4. Redox Reaction
A Reduction Oxidation reaction in which there is a transfer of electrons between chemical species, which actually refers to a chemical reaction in which both oxidation and reduction takes place.
5. Precipitation or Double-Displacement Reaction
The type of displacement reaction in which two compounds reacts each other and consequently, their anions and cations switch places forming two new products, ie., two ions are displaced, hence the name double displacement.
The reactions are represented using chemical symbols. Wonder what? We will discuss it in another blog.