Types of chemical reactions

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What are chemical reactions ?

  • Chemical reactions are the processes by which chemicals interact to form new chemicals with different compositions.
  • Simply, a chemical reaction is the process where reactants are transformed into products.

What are chemical reactions

  • A reactant is a substance that is present at the start of a chemical reaction and a product is a substance that is present at the end of a chemical reaction.

Types of chemical reactions

Following are the principal types of chemical reactions :

Combination or synthesis reaction

In combination reaction, two or more substances (i.e. reactants) unite together to produce a new substance (i.e. product).

Examples :

Combination or synthesis reaction

Decomposition or analysis reaction

In this reaction, a single compound is decomposed or broken into two or more products.

Examples :

Decomposition or analysis reaction

Displacement or Replacement or Substitution reaction

The process of displacing one of the constituents of a compound and occupying its position by another constituent is called displacement reaction or replacement reaction.

It is of two types – single displacement and double displacement reactions.

Single displacement reaction :

In this reaction, one element displaces another element from a compound.

Substitution reaction

Examples :

Single displacement reaction

Double displacement reaction :

In this reaction, there is mutual exchange of ions between two pairs of reacting compounds.

Examples :

Double displacement reaction

Substitution reaction usually occurs in solution and reaction is also known as precipitation reaction.

The reaction in which formation of an insoluble solid (precipitate) takes place by reacting two or more than two aqueous reagents is called precipitation reaction.

Acid – base reaction or Neutralization reaction
  • A chemical reaction in which acid reacts with base to give salt and water is called acid base reaction or neutralization reaction.
  • It is also a double displacement reaction. Examples :

Neutralization reaction

Hydrolysis reaction
  • A chemical reaction which is done by the action of water on any substance to form product is known as hydrolysis.
  • It is the interaction of ions of salt with water to produce acidic or basic solution. Examples:

a) Sodium carbonate dissolves in water to produce strong base and weak acid (i.e. basic solution).

Hydrolysis reaction

b) Ferric chloride is dissolved in water to produce strong acid and weak base (i.e. acidic solution).

Rearrangement or isomerisation reaction
  • Formation of a new compound due to the internal change in position of atoms or groups in the molecule without any loss or gain of atoms is called rearrangement reaction.
  • In this reaction, the molecular formula of the reactants and products remains same but the structure will be different.

Examples :

Rearrangement or isomerisation reaction

Polymerization reaction

The reaction in which the small molecules (monomers) combine to form giant molecule (polymer) is called polymerization reaction. It is of two types.

a. Addition polymerization reaction

b. Condensation polymerization reaction

a. Addition polymerization reaction :

The reaction in which polymer is formed by combination of monomers without elimination of smaller molecules is called addition polymerization reaction.

Polymerization reaction

b. Condensation polymerization :

The reaction in which polymer is formed by combination of monomers with elimination of smaller molecules like water, CO2, etc. is called condensation polymerization.

Example: pyrosulphuric acid (oleum) is obtained by combination of sulphuric acid molecules with the removal of water molecule.

Condensation polymerization

Redox reaction
  • A chemical reaction involving both oxidation and reduction process is called redox reaction.
  • Redox reactions are the chemical reactions in which the reactants undergo a change in their oxidation states. Examples :

Redox reaction

Redox reaction

The loss of electrons and then increase in the oxidation state (number) of a reactant is called oxidation.

The gain of electrons and then decrease in the oxidation number of a reactant is called reduction.

Reversible and Irreversible reactions
  • Chemical reactions in which the products formed interact (react) with each other under suitable conditions to give back the original reactants are called reversible reactions.
  • It is represented by two half arrows between the reactants and the products i.e. one arrow pointing towards products and other pointing towards the reactants. Examples :

  • Chemical reactions in which the products formed do not react with each other to form the original reactants are called irreversible reactions. Examples :

Exothermic and Endothermic reactions
  • A chemical reaction which takes place with the evolution of heat is called an exothermic reaction. Examples :

  • A chemical reaction which takes place with the absorption of heat is called an endothermic reaction. Examples :

References