5. 

13. Moving particle theory
 The word ‘kinetic’ relates to the idea of
movement.
 Kinetic theory can be used to explain the
properties of solids, liquids and gases.
The moving particle theory suggests that
all material is made of extremely small
moving particles. In general, particles
move fastest in gases. When we heat up
a substance, what we really are doing is
making the particles faster.

14. Particles inside a solid
 The particles in a solid are all close
together. They are also more or less
fixed in their positions. They don’t move
too far away from this position because
they are strongly attracted to nearby
particles. This is why solids have a fixed
shape.

15. Particles inside a liquid
 When energy is give to a solid, the
particles vibrate more. They move
farther away from the average central
position and from one another.
Attractions between particles become
weakened, so the particles can move
around more. The solid becomes a liquid.

16. Particle inside a gas
 When energy is given to a liquid, again
the particles begin to move around more.
The particles move around faster until
the attractions between them is not
strong enough to hold them together.
They escape the liquid to become a gas.
They can now move very far apart from
one another. The particles can move
quickly to any part of the container.

17. We all know ice melts if it is left in the
sunshine. This melting is called change of
state. The state of a substance depends on
the environment that surrounds and affects
it. What we know as natural gas on Earth is
a solid at a normal temperature and
pressure. In one sense, a gold ring is just
‘frozen’ gold. Heat gold up and it turns into
a liquid that can be poured into moulds to
make jewellery and gold nuggets.
Change Of State

18. Melting and boiling points

19. Melting points
 The melting point is the temperature at
which a solid changes into a liquid.
 Heating up a solid will cause particles to
vibrate faster.
 At certain temperature, the particles have
energy to break away from their solid
positions and turn into liquid.

20. Boiling point
 The boiling point is the temperature at
which a liquid change to a gas.
 The particles have enough energy to break
away from liquid and turn into gases.
 Example : Water boils at 100 degree Celsius

21. Evaporation
 When liquids are heated above their boiling
points they turn into gases and this process
is called evaporation.
 Evaporation takes energy from surroundings
and causes cooling,
 eg: acetone or alcohol evaporating on our
hand,
clothes getting dry by evaporation.

22.  The process in which water vapour condenses
to form liquid water is called condensation.
 Condensation is the opposite of evaporation
 The stages of condensation are
Evaporation Gas Condensation liquid.