NCERT STD 7 SCIENCE UNIT 6 Physical and Chemical Changes UNIT TEST PDF

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Physical and Chemical Changes

We see different types of changes; every day in our surrounding. Growth of tree, rising of sun, setting of sun, different shape and size of moon, burning of coal, paper, wood, etc. are the examples of changes around us.
Before knowing the scientific meaning of changes; it is necessary to understand some terms, i.e. physical properties, chemical properties, reversible and irreversible.
Physical Properties: Shape, Size and State of substance are known as physical properties. For example; when a sheet of paper is folded, its shape changes and this is an example of change in physical property.
Chemical Properties: The internal properties of a substance are known as chemical properties. For example curd is the product of milk but the internal properties of milk and curd are completely different.

Reversible: Things or processes which can be reversed are called reversible. For example, a folded sheet of paper can be unfolded and hence folding a sheet of paper is reversible.
Irreversible: Things or processes which cannot be reversed are called irreversible. For example, when milk turns into curd; it cannot be changed back to milk and hence is an irreversible change.

Physical Change:

Change in which only physical properties of a substance change and no new substance is formed is called Physical Change.
Most of the physical changes are reversible, this means we can get the substance back even after the change.
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By Nikunj Savani

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