Sample Notes: Solid, Liquids and Gases
O Level and IGCSE Chemistry – Detailed Notes
Chapter 1.1: Solids, Liquids and Gases
Distinguishing Properties of Solids, Liquids and Gases
Solids
- Fixed shape and fixed volume
- Cannot be compressed (particles are tightly packed)
- Do not flow easily
- High density
- Particles vibrate in fixed positions
- Strong intermolecular forces
Liquids
- Fixed volume but no fixed shape (take shape of container)
- Slightly compressible (particles are close but can move past each other)
- Flow easily
- Moderate density
- Particles move over and around each other
- Weaker intermolecular forces than solids
Gases
- No fixed shape or volume
- Highly compressible (particles are far apart)
- Flow freely and fill entire container
- Low density
- Particles move rapidly and randomly in all directions
- Almost no intermolecular forces
Particle Structure of Solids, Liquids and Gases
| State | Separation | Arrangement | Motion |
|---|---|---|---|
| Solid | Very close together | Regular and tightly packed | Vibrate about fixed positions |
| Liquid | Close together | Random, irregular | Slide over each other |
| Gas | Far apart | Random and widely spaced | Rapid and random motion in all directions |
Changes of State (Kinetic Particle Theory)
Melting
- Solid → Liquid
- Heat energy absorbed → increases kinetic energy
- Particles vibrate faster → overcome attractive forces
- Regular structure breaks down → becomes liquid
Boiling
- Liquid → Gas
- Occurs at boiling point
- Particles gain enough energy to escape from liquid surface
- Large increase in movement and volume
Evaporation
- Surface-level liquid → Gas (below boiling point)
- Only high-energy particles escape
- Causes cooling effect (used in sweating)
Freezing
- Liquid → Solid
- Loss of heat energy → particles move more slowly
- Intermolecular forces bring particles into fixed positions
Condensation
- Gas → Liquid
- Particles lose energy
- Move slower and come closer
- Attractive forces pull them into a liquid state
Heating and Cooling Curves (Explained by Kinetic Particle Theory)
Heating Curve
- Temperature rises as kinetic energy increases
- Flat sections: melting point and boiling point
- Energy used to overcome forces between particles, not raise temperature
- Key points:
- AB: solid heats up
- BC: melting
- CD: liquid heats up
- DE: boiling
- EF: gas heats up
Cooling Curve
- Temperature falls as particles lose energy
- Flat sections represent freezing and condensing
- Energy released during formation of bonds
- Key points:
- FA: gas cools
- ED: condensing
- DC: liquid cools
- CB: freezing
- BA: solid cools
Effects of Temperature and Pressure on Gases (Kinetic Particle Theory)
Temperature Increase
- Particles move faster (more kinetic energy)
- More frequent and forceful collisions with container walls
- Volume increases if pressure is constant (Charles’ Law)
Pressure Increase
- Compresses gas → particles closer together
- More frequent collisions
- Volume decreases if temperature is constant (Boyle’s Law)
Summary Table
| Factor | Effect on Gas |
|---|---|
| Increase temp | Faster particles, higher pressure if volume fixed |
| Decrease temp | Slower particles, lower pressure if volume fixed |
| Increase pressure | Particles pushed closer, volume decreases |
| Decrease pressure | Particles spread out, volume increases |
Real-Life Applications
- Car tires: Pressure increases on hot days due to faster particle movement.
- Aerosol cans: Warning to avoid heat exposure as pressure inside rises.
- Refrigerators: Use evaporation of liquids (cooling effect).
- Steam burns: More dangerous than boiling water due to extra latent heat of vaporisation.