Page 340 - Physics Coursebook 2015 (A level)

Cambridge International A Level Physics
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Figure 21.1 At regular intervals of time, the White Lady Geyser, near Rotorua in New Zealand, throws up a plume of water and steam.
From water to steam
When water boils, it changes state – it turns to steam. A liquid has become a gas. This is a familiar process, but Figure 21.1 shows a dramatic example of such
a change of state. This is a geyser in New Zealand, formed when water is trapped underground where
it is in contact with hot rocks. The temperature and pressure of the water build up until it suddenly erupts above the surface to form a tall plume of scalding water and steam.
Changes of state
a
b
c
In this chapter, we will extend these ideas to look at the
energy changes involved when materials are heated and
cooled. b a liquid and c a gas.
The kinetic model of matter can be used to describe the structure of solids, liquids and gases. You should recall that the kinetic model describes the behaviour of matter in terms of moving particles (atoms, molecules, etc.). Figure 21.2 should remind you of how we picture the three states of matter at the atomic scale:
■■ In a solid, the particles are close together, tightly bonded to their neighbours, and vibrating about fixed positions.
■■ In a gas, the particles have broken free from their neighbours; they are widely separated and are free to move around within their container.
QUESTION
1 Describe a liquid in terms of the arrangement of its particles, the bonding between them and their motion.
Figure 21.2 Typical arrangements of atoms in a a solid,