What is a Chemical Reaction – [ Definition, Equations, Examples ]

At the end of the article, you will able to describe – What is a Chemical Reaction, Definition, chemical reaction equations and examples. Let’s start discussing one by one.

What is a Chemical Reaction – Definition

Chemical reactions are the processes in which a new substance with the new properties is formed. It involves chemical changes.

Must Read: Physical and Chemical Changes.

It is not necessary that chemical reactions can be carried only in the science laboratory. A large number of Chemical reactions keep occurring in our daily life. Soaring of milk, a formation of curd, cooking of food, digestion of food, a process of respiration, fermentation of grapes, rusting of iron, burning of a candle, ripening of fruits all is chemical change. In all this case is the identity and nature of substance changes because the chemical reaction takes place in it.

Chemical Reaction Equations

  • Reactant: The substance which takes part in the chemical reaction.
  • Product: The new substances produced as a result of chemical reactions.

Reactant → Product

In reactions, the substances to react, we call substances as a reactant and convert into new substance called product. During the reaction rearrangement of atoms takes place. As a result, a new substance from after the reaction has entirely different properties. A change involves breaking of old Bond and making of the new chemical bond of a new substance.

During process atoms of one element do not change into another element. The only rearrangement of atoms takes place in a reaction. In a given diagram methane reacts with oxygen to form carbon dioxide and water. A change is taking place which involves the rearrangement of elements.

What is Chemical Reaction

Chemical Reaction Examples

In a chemical reaction, reactant reacts to change into the product.

During the process, Important characteristics may occur

  • Evolution of gas.
  • Formation of precipitation.
  • Change in color.
  • Change in temperature and
  • Change in the state.

Anyone of these general characteristics tells us whether a reaction took place or not. For example: On mixing two substance, if a gas evolves. Then we can say a chemical change has taken place. Similarly for others characteristics.


The Following reaction showing the combustion of methane (CH4) in oxygen (O2). In this process when methane is burned it releases out the Carbon dioxide (CO2) and Water(H2O).

CH(g)+2O(g)CO2(g)+2H2O(l                   ΔH=890.4kJ

Here the ΔH is the heat evolved. This causes the change in Temperature.

  • ΔH = +ve (Heat absorbed)
  • ΔH = -ve (Heat Release)

This is all about the basics of – What is a Chemical Reaction, Definition, chemical reaction equations and examples.