Page 35 - 新思维科学学生用书7 样章

2 Materials and their structure

Changing state

If you leave ice in a warm place it melts and becomes liquid water. The temperature at which a solid
melts is called the melting point.

Water on the ground will gradually disappear as it changes to water vapour, an invisible gas. This is

called evaporation. The warmer the water, the more quickly it evaporates.
If you heat water until its temperature reaches 100 °C, it will boil. All of the water rapidly changes to

steam. Steam is water heated to the point that it turns into a gas. 100 °C is the boiling point of water.

If the water vapour or steam touches something cold, it condenses and changes back to liquid water.
This is called condensation.

If you put liquid water in the freezer, it freezes and becomes ice.

These changes are known as changes of state.

steam water ice
boiling melting

condensing freezing

Activity 2.2.1

Which change of state?
Work in pairs.

Cut out nine rectangles from a piece of A4 card. Write these words onto the cards:
melt, freeze, condense, boil, liquid, gas, solid, from, to.

One of you should have the change of state cards (melt, freeze, condense, boil). The
other should have the remaining cards (liquid, gas, solid, from, to).

Hold up a change of state card. Your partner should then select the correct cards to

show which state is changing to which other state. For example: ‘freeze’ would be
from ‘liquid to solid’.

Swap the sets of cards so that you take turns.

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