Study Notes
The particle model of matter explains how substances change state without changing the number of molecules, only their energy. Changes of state are physical and reversible processes.
- Density — the mass per unit volume of a material. Example: Density = Mass/Volume, ρ = m/V.
- Melting — occurs when a solid turns into a liquid. Example: Ice turning into water.
- Freezing — occurs when a liquid turns into a solid. Example: Water turning into ice.
- Boiling — occurs when a liquid turns into a gas. Example: Water boiling to become steam.
- Condensing — occurs when a gas turns into a liquid. Example: Steam condensing into water.
- Evaporation — occurs when particles at the surface of a liquid gain enough energy to become gas. Example: Water evaporating from a puddle.
Exam Tips
Key Definitions to Remember
- Density: mass per unit volume
- Melting: solid to liquid
- Freezing: liquid to solid
- Boiling: liquid to gas
- Condensing: gas to liquid
- Evaporation: surface liquid to gas
Common Confusions
- Confusing boiling with evaporation; boiling occurs throughout the liquid, evaporation only at the surface.
- Thinking mass changes during state changes; it remains constant.
Typical Exam Questions
- What is density? Density is mass per unit volume.
- How does boiling differ from evaporation? Boiling occurs throughout the liquid at boiling point, while evaporation occurs at the surface at any temperature.
- What happens to particle energy during melting? Particles gain kinetic energy and move more freely.
What Examiners Usually Test
- Understanding of the particle model and changes of state.
- Ability to calculate density using the formula ρ = m/V.
- Differences between boiling and evaporation.