Changes around us – Introduction, Changes, Types

Changes Around Us – Physical and Chemical Changes explained with examples

This article aims to delve into the different kinds of changes seen around us such as physical changes and chemical changes with various examples from the perspective of the SSC CGL/CHSL and banking examinations.

Reversible change: Changes after which the object can be bought back to its original state or in simple words, be reversed are called reversible changes. E.g. Changing water to ice, stretching of a rubber band.

Irreversible change: Changes after which the object cannot be bought back to its original state or irreversed are called irreversible changes. Eg. Burning of a substance.

Physical Changes: when there are changes in the physical properties of the
substance, they are known as physical changes.

Physical properties include size, color, shape, temperature, state, odor,
appearance, texture, etc.

In a physical change, the substance does not change, only its molecules get

Physical Changes do not lead to formation of a new substance.

They are mostly reversible (melting of gold) but can also be irreversible (increase in height of a human) in nature.

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Examples of physical changes around us:

 Blowing air into a balloon.
 Melting of gold, silver and other metals.
 Dissolving sugar into water. Even though sugar disappears and dissolves in water, the individual sugar molecules don’t change, they just get dispersed.
 Increase in height of a human.


The method through which crystals of a substance are formed from its liquid form is called crystallization.

This is a physical change.

Chemical Changes: When there are changes in the chemical properties of a
substance they are known as chemical changes.

When substances react with other substances around them, they often lead to the formation of a new substance which is a key indicator of a chemical change.

The formation of a new substance is often accompanied by:

a) Emission of Heat (Exothermic Reaction)
b) Absorption of Heat (Endothermic Reaction)
c) Emission of Light
d) Production of sound
e) Change or emission of odor
f) Emission of Gas

They are mostly irreversible in nature (burning of wood, baking of a cake) but can also be reversible (creation of Nitrogen dioxide from nitrogen monoxide and oxygen)

Chemical changes involve a change in the composition of the molecules of the substance.

Examples of Chemical changes are:

a) Rusting of iron
b) Souring of milk

c) Digestion of food
d) Setting of cement
e) photosynthesis

Rusting of Iron (4FE + 3O2 = Fe2o3)

Deposition of a brown layer on iron is called rusting which is formed due to
reaction of oxygen with iron. Rusting leads to the formation of a new product that is iron oxide which does not let iron retain the properties it is used for in the society E.g being a strong metal and causes large monetary losses to people. Hence, a lot of precautions are taken to avoid iron to come in direct contact with air.

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Painting adds a layer of coating which prevents the iron to come in direct
contact with oxygen.

Grease is used similarly to cut off the contact of air with iron.


Galvanization is a process in which a non reactive metal such as zinc is
deposited over iron to prevent it to come in direct contact with air and thus
prevent rusting.

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