Can states of matter be changed?

Preparation

Content focus: How solids, liquids and gases can be changed

Investigative skills focus: 

Questioning and predicting

Planning and conducting

Processing and analysing data and information evaluating

Communicating

Collect all the materials required for the experiments on the experiment page.

Introduction

Background information

• Some changes of matter are physical (reversible). They can change appearance or state through bending, heating, stretching etc. but are still the same material and can be changed back. (Sometimes this is a complex process, such as those dealing with evaporation to extract salt that has been dissolved in water.) Other changes can be chemical (irreversible). Through heating, burning, cooking etc., a new substance is made and cannot be changed back.
• The temperature at which a solid turns into a liquid is called the melting point; the temperature at which a liquid turns into a gas is called the boiling point.
• A gain in heat by a state of matter is called an endothermic change; a loss in heat is called an exothermic change.
• Most substances follow the normal changes of state when they are heated (i.e. from solid to liquid to gas) and the reverse if they are cooled. A few can move directly from solid to gas, without becoming a liquid first. This is the process called sublimation (as shown on the diagram on page 39). Dry ice (solid carbon dioxide) is a good example of this process. Mothballs and some types of solid air fresheners are also examples. The reverse of sublimation is deposition.

Development

• Allow the pupils to read the text on student page slides independently, but assist with unknown vocabulary if necessary.
• Discuss the text when they have finished reading it to ensure they understand the concepts presented.

Differentiation

• The artworks created by completing the activities using evaporated coloured water can be used to create sun catchers or hanging decorations. Cut into shapes, punch a hold at the top and hang using string.

Conclusion

• Discuss with the students after the activity how the experiment worked or didn’t work, what might have gone wrong, and what they would change to make it better.

Assessment

Page 40

1. 1. (a) matter, (b) molecules/atoms, (c) solid, (d) liquid, (e) gas
   2. Heat, when applied, makes the molecules speed up; cold makes the molecules slow down.
   3. (a) When heat is applied to a solid, the molecules speed up and the forces between them become weaker. The molecules separate and form a liquid.
      (b) When a gas is cooled, the molecules slow down and the forces among them increase. The molecules move closer together to form a liquid. As the temperature continues to decrease, the molecules in the liquid move even closer together to form a solid.
   4. Starting state: solid, liquid, gas, liquid
      Changed state: liquid, solid, liquid, gas
      Name of process: melting, freezing, condensation, evaporation

The work of scientists question
Use and influence of science
Answers will vary. The pupils could list wood or coal as solid forms of heating and cooking in the home and natural gas as another. (Electrical forms of heating and cooking cannot be included in any of the categories since they are a force rather than a state of matter.) Some pupils might include safety or environmental issues relating to the use of wood, coal and gas for heating and cooking in the home. These should be considered as a class.