AQA GCSE PHYSICS · PAPER 1 · FOUNDATION & HIGHER
Changes of state
Particle model of matter · Lesson 2 of 6
Warm-up
Answer each one, then check.
1. What is the change from solid to liquid called?
Melting
2. What is the change from gas to liquid called?
Condensing
3. What is the unit of mass?
Kilogram
4. What is freezing?
Liquid to solid
5. Give an example of a chemical change.
Burning wood
Learning Objectives
1. Name each change of state.
2. Explain that mass is conserved in a change of state.
3. Explain that changes of state are physical changes and are reversible.
4. Draw and interpret particle diagrams for solids, liquids and gases.
Changes Of State
Changes of state are physical changes: the material recovers its original properties if the change is reversed. Mass is conserved.
The particles are the same before and after, so the mass is the same. Only the arrangement and energy of the particles change.
Six Changes of State
|
Heating goes one way; cooling reverses it. |
A diagram of melting, freezing, boiling, condensing and sublimation between solid, liquid and gas.
The Changes
Learn the names.
|
Change |
From |
To |
Energy |
|---|---|---|---|
|
Melting |
Solid |
Liquid |
Energy taken in |
|
Freezing |
Liquid |
Solid |
Energy given out |
|
Boiling or evaporating |
Liquid |
Gas |
Energy taken in |
|
Condensing |
Gas |
Liquid |
Energy given out |
|
Sublimation |
Solid |
Gas |
Energy taken in |
Mass in a Change of State
|
A 200 g ice cube melts to form water. What is the mass of the water? Explain. |
1. Number of particles
The same particles are present as liquid water
2. Mass
Unchanged, because no particles are lost
Answer: 200 g: mass is conserved.
Physical or Chemical?
|
Explain why melting ice is a physical change but burning wood is a chemical change. |
1. Melting ice
The water is the same substance, and it freezes back to ice with the same properties
2. Burning wood
New substances are made and the wood cannot be recovered
Answer: Physical changes are reversible and the material recovers its original properties.
Particle Explanation
Say what the particles do.
▸ Melting. Particles gain energy and break free from their fixed positions.
▸ Boiling. Particles gain enough energy to overcome the attractions and move far apart.
▸ Condensing and freezing. Particles lose energy and get closer.
Key Terms
|
Melting Solid to liquid. |
Freezing Liquid to solid. |
|
Boiling Liquid to gas throughout the liquid. |
Evaporating Liquid to gas at the surface. |
|
Condensing Gas to liquid. |
Sublimation Solid straight to gas. |
Your Task: Name the Change
8 minutes
|
Name each change: (a) water becomes steam; (b) steam becomes water on a cold window; (c) a puddle freezes; (d) dry ice becomes carbon dioxide gas without becoming liquid. 1. Name the start and end state. 2. Choose the change. |
A good answer shows: (a) Boiling (or evaporating). (b) Condensing. (c) Freezing. (d) Sublimation.
Can I...?
☐ Name all the changes of state.
☐ Say whether energy is taken in or given out.
☐ Explain that mass is conserved.
☐ Explain physical changes.
☐ Draw solid, liquid, gas particles.
☐ Explain melting with particles.
☐ Distinguish physical and chemical.
☐ Give an example of sublimation.
Summary
✓ Melting, freezing, boiling, condensing, sublimation.
✓ Mass is conserved.
✓ Physical changes are reversible.
✓ Particles' energy changes but the particles stay the same.
|
EXAM FOCUS Name the change of state when a liquid becomes a solid. (1 mark) Freezing. |