Page 101 - ICSE Science 3 : E-book

9

Water as a Resource

Water is important for life on earth. When KEY CONCEPTS

our earth is seen from the space, it appears
• Change of state of water
blue in colour. This is because most of the
• Water cycle
earth’s surface is covered with water.
• Water and impurities
All living things need water to survive. It • Purifi cation of water
is one of the most valuable resources for • Rainwater harvesting

us because majority of our daily activities
depend on water.

We have already learnt in the previous chapter that water can change its form by
heating or cooling. It can exist in all the three forms—solid (ice), liquid (water) and

gas (water vapour).

Let’s learn more about the change of state of water.

Change of State of Water

The change of state of water occurs because of temperature changes. Let’s study
how it happens.

• When the temperature at which ice
I change into ice
is kept is increased, it changes into on freezing.

water. This change is called melting.
I change into
• When water is heated or its gas on heating.
temperature is increased, it changes

into water vapour. This change

is called evaporation when the
heating process is slow, while it is
I change into
called boiling when the heating is liquid on cooling.
fast.

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