Currently Empty: $0.00
Lesson 3: Changes of State Melting, freezing, boiling, condensing Particle explanation of state changes Heating and cooling (qualitative)
Year 8 • Chemistry
Lesson 3: Changes of State
In this lesson, students learn how substances change state through heating and cooling. Melting, freezing, boiling, and condensing are explained using the particle model.
Lesson Objectives
- Describe melting, freezing, boiling, and condensing.
- Explain changes of state using particles.
- Understand the effect of heating and cooling.
- Apply ideas to everyday examples.
1. What Is a Change of State?
A change of state happens when a substance changes between solid, liquid, and gas.
The substance remains the same, only the arrangement and movement of particles change.
[ Image Placeholder – Changes of State Diagram ]
Key idea:
• Changes of state are physical changes
• No new substance is formed
• Changes of state are physical changes
• No new substance is formed
2. Melting and Freezing
Melting occurs when a solid changes into a liquid by heating.
Freezing occurs when a liquid changes into a solid by cooling.
[ Image Placeholder – Melting and Freezing ]
Particle explanation:
• Heating gives particles more energy
• Particles vibrate more and break free (melting)
• Cooling removes energy and particles lock into place (freezing)
• Heating gives particles more energy
• Particles vibrate more and break free (melting)
• Cooling removes energy and particles lock into place (freezing)
Real-life example:
Ice melting into water and water freezing into ice.
3. Boiling and Condensing
Boiling happens when a liquid changes into a gas by heating.
Condensing happens when a gas changes into a liquid by cooling.
[ Image Placeholder – Boiling and Condensing ]
Particle explanation:
• Boiling gives particles enough energy to escape
• Gas particles are far apart and move freely
• Cooling removes energy and particles come closer (condensing)
• Boiling gives particles enough energy to escape
• Gas particles are far apart and move freely
• Cooling removes energy and particles come closer (condensing)
Real-life example:
Steam from boiling water condensing on a cold window.
4. Heating and Cooling (Qualitative)
Heating and cooling affect how particles move.
This lesson focuses on understanding these effects without calculations.
[ Image Placeholder – Heating and Cooling of Particles ]
• Heating → particles gain energy and move faster
• Cooling → particles lose energy and move slower
• Energy change causes state change
• Cooling → particles lose energy and move slower
• Energy change causes state change
Practice Questions
A. Fill in the Blanks
- Melting changes a __________ into a liquid.
- Freezing happens when energy is __________.
- Boiling changes a liquid into a __________.
- Condensing happens when a gas is __________.
- Changes of state are __________ changes.
B. True or False
- Melting needs heating.
- Freezing adds energy.
- Boiling gives particles more energy.
- Condensing forms a new substance.
- Particles move faster when heated.
C. Short Answer
- What happens to particles during melting?
- Why does boiling need heating?
- What causes condensing?
- Is a change of state chemical or physical?
- Give one example of a change of state.
✅ Show Answer Key
A. Fill in the Blanks
- solid
- removed
- gas
- cooled
- physical
B. True or False
- True
- False
- True
- False
- True
C. Short Answer
- Particles gain energy and move freely.
- Particles need energy to escape.
- Cooling removes energy.
- Physical.
- Ice melting / water boiling (any).
© Aviate Learning – Changes of State (Year 8)