Page 17 - Curriculum Visions Dynamic Book

(Above and above right)
Freezing and the development of ice crystals and melting.
(Below) Sometimes water can change directly from a gas
to a solid without forming a
liquid in-between. This is called sublimation, and it is shown when ice forms on cold surfaces. We then call it hoarfrost. Under strong heating ice can also evaporate, forming water vapour without becoming a liquid in-between, and this too is called sublimation.
(Right) As the molecules in a solid are “excited” by an increase in energy, such as by heating, they split apart, and the solid melts.
Getting hotter
The lattice structure of the solid breaks up into clumps as it melts.
(such as latex) consist of hundreds or thousands of atoms. Although they can be both liquids and solids, they can never be gases. When they are heated, the atoms all split apart, and the liquid decomposes instead of evaporating.
Changing between states
For a liquid to change to a gas or solid, there must be a change in its energy. For example, liquid water possesses enough energy to stop the attractive forces between molecules from fixing it into the rigid
solid structure (ice), but it does not have enough energy to allow each molecule to move away from its neighbours and form a gas (water vapour). So, when a liquid changes into a gas, it must gain some extra energy; and when it changes from a liquid to a solid, it must lose some energy. The energy gain or loss is called latent heat.
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