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Examples are breaking of mirror, burning of coal etc.

According to external and internal changes, the changes are classified into two
groups.

They are physical changes and chemical changes.

Physical Change:

A change where no change in the internal properties of the substances and no new
substance is formed is called a physical change. Physical changes are reversible or
irreversible in nature.

As for example, melting of ice, tearing of page, folding of a sari.

Characteristics of Physical Change:-

 No new substance is formed.
 Change may be reversible or irreversible in nature.
 No change in the internal structure.

Chemical Change:-

A change in which new substances are formed whose properties are entirely
different from the previous substance.

Examples of chemical changes are curdling of milk, growth of a plant, Burning of
paper etc.

Characteristics of chemical reaction:-

 A new substance is formed.

 Change occur in internal structure.
 Irrevesible in nature.
 Heat may be evolved or absorbed.
 Some Common Chemical Changes
 Rusting of iron
 Iron objects react with oxygen and moisture present in air to produce flaky
reddish brown colour substance is commonly known as rust.
 Iron + Oxygen + Water  Rust (hydrated iron oxide)
(Fe) (O2) (H2O) (Fe2O3. xH2 O)

Methods of prevention of rusting:

1. Applying grease or oil on the exposed part of the iron articles.
2. Painting the surface of iron article.

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