Knowledge and Understanding 1. Fig. 20 shows the arrangement of particles in a solid, a liquid and a gas. (a) Which diagram
shows a gas? (b) Name the physical changes that take place when B changes into A. A
B C
Fig. 20
2. Explain what happens to the particles in a solid while it is melting. 3. Explain what happens to the particles in a liquid while it is boiling. 4. Study the diagrams in Fig. 21 carefully. They show the way in which particles of gases and solids occupy space. The particles of a gas have lots of space and move randomly at high speeds in three dimensions, colliding with each other and with their container. The arrows represent the movements of the gas particles. The particles of a solid are packed closely together and cannot move around but they can vibrate. Give one property of a gas and one property of a solid that you have observed which matches this particle view of these states of matter.
Fig. 21 T I
Thinking and Investigating 1. Why do you think it is important to have standardised weights and measures around the world?
2. How does an understanding of the atomic nature of matter help to explain changes of state? 3. How does the atomic nature of matter explain the conservation of mass during a chemical change?
4. When water freezes it expands. Does this mean that its mass increases? Explain your answer by referring to the atomic nature of matter.
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5. Give two everyday examples of (a) melting (b) freezing and (c) evaporating. 6. Air is matter. How would you show that it occupies space and has mass? 7. Describe how the particles are behaving when (a) water vapour turns to liquid water and (b) liquid water turns to ice.
