Page 33 - ICSE Chemistry 8

Take a Break!

Write/Choose the correct answer.
1. Precipita on is a periodic change. (True/False)
2. Some changes are benefi cial and some are not. (True/False)

3. Changes that occur on their own, i.e., without any human eff ort are called ____________.
4. Changes that occur very quickly are called ________ changes.
5. The revolu on of the earth is a ________ (natural/man-made) change.

PHYSICAL AND CHEMICAL CHANGES

All kinds of changes discussed earlier in the chapter can be broadly classifi ed into two types.
• Physical changes • Chemical changes

Physical Changes

Changes in which only the physical proper es of a substance change
Physical Proper es
without any change in its composi on are known as physical changes.
Proper es of a substance such
During physical changes, new substances are not formed and such as size, shape, colour and state
changes are generally reversible in nature. are called physical proper es.

Characteristics of a Physical Change
• A physical change is temporary and reversible.

• The composi on of the substance does not change during a physical change.
• No new substance is formed during a physical change.

• During a physical change, only physical proper es like size, shape, colour and state of the substance
change.
• No major gain or loss of energy takes place in a physical change. The energy needed to bring about
a physical change is equal to the energy needed to reverse the change.

• No change of mass occurs during a physical change. This is because the substance undergoing a
physical change remains the same. No ma er is added or removed.

Examples of Physical Change
• Breaking of a glass plate: A glass plate sha ers into many pieces when it breaks. Each broken piece
of the plate is s ll glass and no new substance is formed. Hence, the breaking of a glass plate is
considered to be a physical change.

• Drying of wet clothes: Evapora on of water takes place when wet clothes dry. The water in the
clothes changes to its vapour state on absorbing heat from the surroundings. Therefore, drying of
wet clothes is a physical change.
• Mel ng of ice: It involves a change from solid state of water to its liquid state. There is no change
in the proper es of the substance and no new substance is formed. Hence, mel ng of ice is a
physical change.

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