Physics A Level
Chapter 19: Thermal physics 19.1 Changes of state
Physics A Level
Chapter 19: Thermal physics 19.1 Changes of state
FROM WATER TO STEAM
When water boils, it changes state – it turns to water vapour. A liquid has become a gas. This is a familiar process, but Figure 19.1 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 water vapour. What happens underground to cause this effect? Would this be a useful effect to have happen near where you live?
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, and so on). Figure 19.2 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.
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Question
1) Describe a liquid in terms of the arrangement of its particles, the bonding between them and their motion.
In this chapter, we will extend these ideas to look at the energy changes involved when materials are heated and cooled.