STD IX – CHEMICAL CHANGES AND REACTION – (Online)

Types of Chemical Changes

Combination reaction

Two or more compounds combine to form one compound.

A + B → AB

Combination reaction is also known as a synthesis reaction.

Example of combination reaction: 2Na + Cl2 → 2NaCl

Decomposition reaction              

The opposite of a combination reaction – a complex molecule breaks down to make simpler ones

AB → A + B

A decomposition reaction is just the opposite of combination reaction.

Example of a decomposition reaction: CaCO3 → CaO + CO2

The reaction in which a compound decomposes due to heating is known as a thermal decomposition reaction.

Displacement reaction 

One element takes place with another element in the compound.            

A + BC → AC + B                               

It takes the form X + YZ → XZ + Y

It is also called a substitution reaction

Example of displacement reaction: Zn + CuSO4 → ZnSO4 + Cu

Double Displacement Reaction

A chemical reaction in which ions gets exchanged between two reactants which form a new compound is called a double displacement reaction.

It takes the form of XY + ZA → XZ + YA

It takes the form of XY + ZA → XZ + YA

It is also called a metathesis reaction

Example of double displacement reaction:

           BaCl2 + Na2SO4 → BaSO4 + 2NaCl