Page 63 - ICSE Chemistry 6

Diffusion

The phenomenon of intermingling of substances by the natural movement of their par cles is called
diff usion.

Gases: The par cles in gases have enough space between them that allows them to move freely. Hence,
gases diff use very fast.
Liquids: Liquids also diff use but not as fast as gases. Liquids are of two types—miscible and immiscible.
Liquids like milk and water which mix with each other are called miscible liquids. Some liquids like oil and
water do not mix together, and are called immiscible liquids.

Solids: Solids are very rigid and hence do not diff use under normal condi ons or diff use to a very li le
extent.
Brownian Motion

Brownian mo onrefers to the zig-zag movement of small par cles suspended in a medium. This movement
of par cles is caused by the collision of molecules.

Brownian mo on can be observed by suspending some lycopodium (rubber) powder in a beaker that is
half fi lled with water. Using a microscope, it can be seen that par cles of lycopodium move randomly (zig-
zag) throughout water. The movement of the par cles increases further on hea ng the beaker.

EFFECTS OF HEAT ON MATTER

When heat is supplied to a substance, it goes through various changes. Let’s discuss them in detail.

• Change in states of ma er
• Thermal expansion

• Chemical change
Change in State of Matter

Ma er can be changed from one state to the other by supplying or removing heat energy. On hea ng,
the molecules of ma er move rapidly. Due to their con nuous movement, they change from one state
to another. All the three states of ma er are interconver ble. Let’s understand this using water as an
example.

+heat +heat

–heat –heat
solid

liquid gas
Fig. 3.5: The three states of matter and their interconversion

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