chemical reaction | Definition, Equations, Examples & Types

Chemical Reaction 

Physical Reaction

Reactions which result in changes in physical properties are called physical reactions.

Change that can occur in physical reactions:

  1. Change in colour
  2. Change in shape
  3. Change in size
  4. Change in state

Chemical Reaction 

Reactions which result in the formation of new products are called chemical reactions.

  • Changes that can occur in chemical reactions:
  • Evolution of gas
  • Change in colour 
  • Change in temperature 
  • Change in state of a substance 
  • Formation of precipitate 

Chemical Equations

Writing any chemical reactions with the help of formulae of the substance and symbols of the substance is called chemical Equations. There are many different types of chemical reactions that we encounter in our daily life also.


Types of Chemical Reaction

Combination Reaction: 

When two or more two substances undergo a chemical reaction resulting in the formation of one product, this type of chemical reaction is called a combination reaction.


Decomposition Reaction:

 When one reactant decomposes into more than one product, this type of reaction is called a decomposition reaction.


By heating calcium carbonate, we get calcium oxide and carbon dioxide as a product of the decomposition reaction.

Displacement Reaction: 

A reaction in which one element displaces the other is called a displacement reaction.


In the above reaction, zinc displaces hydrogen as zinc is more reactive than hydrogen.

Double Displacement Reaction:

A double displacement reaction occurs as the result of the exchange of ions between two reactants.

NaoH+HCl=NaCl+H2O (neutralisation reaction)

AgNO3+ HClAgCl+NaNO3(precipitation reaction)

Neutralisation reaction and precipitation reaction are examples of the double displacement reaction.

Precipitation Reaction

In a precipitation reaction, two soluble liquids undergo a chemical reaction and form one soluble and one insoluble product. The insoluble product is called a precipitate.

AgNO3+ HCl=AgCl+NaNO3

Netralisation Reaction

The reaction between acid and base results in the formation of the salt and water, this reaction is known as the neutralisation reaction.


Endothermic and Exothermic Reaction

Reaction in which heat absorption from the surrounding take place is called an endothermic reaction.


By heating calcium carbonate, we get calcium oxide and carbon dioxide as a product.

A reaction in which heat is released in the surroundings is called an exothermic reaction.



Q. What is Chemical Reaction?

Ans: A reaction in which new substance formation take place is called a chemical reaction.

Q. Give an example of a double displacement reaction.

Ans: Double displacement reaction, occur as the result of the exchange of ions between two reactants. Example of double displacement reaction; NaoH+HClNaCl+H2O (neutralisation reaction) and AgNO3+ HClAgCl+NaNO3(precipitation reaction)

Q. Is physical change occurs in a chemical reaction?

Ans: Both physical and chemical changes can occur in the chemical reaction.

Q. In chemistry how are any different types of the chemical reaction are there?

Ans: In chemistry, there are mainly five chemical reactions that are: combination reaction, precipitation reaction, displacement reaction, double displacement reaction and decomposition reaction.

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