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Science at key stage 3    (Year 8)

Unit 8I: Heating and cooling
Section 16: How can we explain change of state?

QCA

Objectives
Children should learn:
  • to use the particle model to explain changes of state
  • that solids, liquids and gases can change when energy is added or removed and these changes are reversible
  • that changes of state occur at fixed temperatures
  • to draw an appropriate curve/line to fit quantitative data on a graph

Activities

Outcomes
Children:
  • Ask pupils to use the particle model to predict what might happen if heating of a solid or a liquid eg wax, water, continued indefinitely.
  • Use ICT simulations to illustrate the particle model explanation for melting, boiling, freezing/solidifying.
  • Invite pupils in groups to measure and record every half minute the temperature of one (or more) material as it changes state, eg
    • ice as it melts
    • water as it boils
    • salol (phenyl salicylate) as it melts
    • salol (phenyl salicylate) as it freezes
  • Ask pupils to plot their data on a graph and show them how to draw an appropriate curve, or use temperature probes with a datalogger, to produce a real-time graphic display. Ask pupils to describe or tell the story of what happens to the temperature. Establish through discussion of their data and some data from secondary sources that changes of state occur at a fixed temperature. Challenge pupils to tell the story of what would happen if their particular substance were cooled or heated again.
  • collect data and draw graphs with an appropriate curve to show what happens to the temperature as a material changes state
  • use the terms 'melting point' and 'boiling point' and give some important examples
  • describe what happens to the temperature of the substance, eg the salol got warmer and the temperature stayed the same for three minutes. When it had all melted, the temperature started to go up again
  • describe, with reasons, what would happen if the liquid/solid were cooled/heated again
  • use the particle model to associate heating and cooling with changes of state

Points to note
  • At key stage 2, pupils will have had experience of changes of state and will have used scientific terms for these. They are unlikely to have discussed explanations in terms of particles.
  • Negative numbers are introduced in key stage 1. By the end of key stage 2, pupils should be able to say that -100?C is lower than 50?C. However, they may need practice in adding and subtracting negative numbers.
  • Some pupils may need help in choosing appropriate scales for the axes of their graphs.

    • Safety

    • salol (phenyl salicylate) can be safely heated using a water bath; it is not hazardous

Sections in this unit

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This unit is divided into sections. Each section contains a sequence of activities with related objectives and outcomes. You can view this unit by moving through the sections or print/download the whole unit.
1. a. What's the temperature?
2. b. What's the temperature?
3. a. How do things get hotter or colder?
4. b. How do things get hotter or colder?
5. c. How do things get hotter or colder?
6. d. How do things get hotter or colder?
7. e. How do things get hotter or colder?
8. a. How do materials change when they are heated and cooled?
9. b. How do materials change when they are heated and cooled?
10. c. How do materials change when they are heated and cooled?
11. d. How do materials change when they are heated and cooled?
12. e. How do materials change when they are heated and cooled?
13. a. How can we reduce energy waste?
14. b. How can we reduce energy waste?
15. Checking progress
16. How can we explain change of state?
17. Reviewing work