Good Science Victorian Curriculum Year 7

CHAPTER 4: STATES OF MATTER
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Liquids expand when they are heated
Thermal expansion also happens in liquids. Heating a liquid causes
the particles to move more quickly and further away from each other,
so liquids will take up a larger volume as they become warm. They will
contract as they cool back down again.
Water that is heated without any room to expand can be very
damaging. For example, it can cause pipes to burst. The property of
liquids expanding when heated can be used safely, such as in alcohol
and mercury thermometers. The liquid inside them expands when the
temperature increases.
Why can thermal expansion be a problem?
Figure 4.10 The liquid alcohol inside a
thermometer takes up different amounts
of space depending on how much
heat energy it has, allowing the
temperature to be measured.
Gases expand or contract with changes
in heat
As with solids and liquids, thermal expansion and contraction also
happens in gases. Because the particles in gases are already far apart,
the expansion and contraction of gases can be very noticeable.
Although most gases are invisible, you can still see that a warm gas
will take up more space than a cold gas. You can check this by blowing
up a balloon and putting it in a refrigerator. The gases inside it will cool
down and contract, making the balloon smaller.
How will the volume of a gas change if it is cooled?
Figure 4.11 The gas in a hot
air balloon will expand when
it is heated.
Investigation 4.3
Expanding gases
KEY SKILL
Evaluating results for
reliability and validity
Go to page 151
CHECKPOINT 4.3
1 What happens to the particles
in a substance when heat
energy is added?
2 What happens to the particles
in a substance when they lose
heat energy?
3 Identify which state of matter
(solid, liquid or gas) would
show the greatest change in
volume if heat energy is added
or lost. Use the particle model
to help explain your answer.
4 An iron bar is heated from room
temperature to 300°C. Would
this make the bar expand or
contract? Explain your answer
using evidence from the text.
5 Describe and include a
diagram showing what
happens to the particles in the
iron bar in question 4.
6 Design a safety feature in a
building that would prevent
the walls cracking when they
expand after heating. You could
write a description or draw an
annotated diagram.
CONNECTING IDEAS
7 Bridges have expansion joints
to prevent buckling in hot
weather. What are some other
examples of designs that take
into account how particles
behave in solids, liquids
or gases?
SUCCESS CRITERIA
I can predict the effect of
adding or removing heat on:
solids
liquids
gases.
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