Summary
Changes of state involve the transition of water between solid, liquid, and gas phases through processes like melting, freezing, boiling, and evaporation.
- Melting — the process where ice (solid) gains heat and turns into water (liquid). Example: Ice melts at 0°C, which is the melting point.
- Freezing — the process where water (liquid) loses heat and turns into ice (solid). Example: Water freezes at 0°C, which is the freezing point.
- Boiling — the process where water (liquid) gains heat and turns into water vapour (gas). Example: Water boils at 100°C, which is the boiling point.
- Evaporation — the process where water (liquid) gains heat and turns into water vapour (gas) at any temperature. Example: Evaporation occurs faster at higher temperatures, windy conditions, and with a larger exposed surface area.
- Condensation — the process where water vapour (gas) loses heat and turns into water droplets (liquid). Example: Water vapour condenses on a cooler surface.
Exam Tips
Key Definitions to Remember
- Melting: Ice turns into water at 0°C.
- Freezing: Water turns into ice at 0°C.
- Boiling: Water turns into vapour at 100°C.
- Evaporation: Water turns into vapour at any temperature.
- Condensation: Vapour turns into water droplets.
Common Confusions
- Confusing boiling and evaporation; boiling occurs at a specific temperature, while evaporation can happen at any temperature.
- Misunderstanding that freezing and melting points are the same temperature for water.
Typical Exam Questions
- What happens to ice at 0°C? It melts into water.
- At what temperature does water boil? Water boils at 100°C.
- What factors increase the rate of evaporation? Higher temperature, wind, and larger exposed surface area.
What Examiners Usually Test
- Understanding of the processes of melting, freezing, boiling, evaporation, and condensation.
- Ability to explain factors affecting the rate of evaporation.
- Knowledge of the specific temperatures for melting, freezing, and boiling points of water.