📌 What is Matter?
- Matter is anything that has mass and occupies space.
- Matter is made up of tiny particles (atoms and molecules) that are too small to be seen with the naked eye.
- All matter possesses the properties of mass, weight, volume, and inertia.
Kinetic Theory of Matter: The particles of matter are in a state of constant, random motion. The kinetic energy of particles increases with temperature. There are forces of attraction between particles that vary with distance.
🧊 Three States of Matter — Comparative Properties
| Property | Solid | Liquid | Gas |
|---|---|---|---|
| Shape | Fixed/definite | No fixed shape; takes shape of container | No fixed shape; fills container |
| Volume | Fixed/definite | Fixed/definite | No fixed volume; fills container |
| Compressibility | Nearly incompressible | Nearly incompressible | Highly compressible |
| Inter-particle space | Very small | More than solid | Very large |
| Particle motion | Vibrate about fixed positions | Slide past each other | Move freely and rapidly |
| Forces of attraction | Very strong | Moderate | Very weak |
| Density | High | Moderate | Very low |
🔄 Changes of State
| Change of State | Process | Heat Change | Example |
|---|---|---|---|
| Solid → Liquid | Melting (Fusion) | Heat absorbed | Ice melting at 0 °C |
| Liquid → Solid | Solidification (Freezing) | Heat released | Water freezing at 0 °C |
| Liquid → Gas | Evaporation / Vaporisation (Boiling) | Heat absorbed | Water boiling at 100 °C |
| Gas → Liquid | Condensation (Liquefaction) | Heat released | Water vapour forming dew |
| Solid → Gas (directly) | Sublimation | Heat absorbed | Dry ice (CO₂), camphor, iodine |
| Gas → Solid (directly) | Deposition | Heat released | Frost forming on surfaces |
- Melting point: The temperature at which a solid changes to liquid at standard pressure. (Ice melting point = 0 °C)
- Boiling point: The temperature at which a liquid changes to gas at standard pressure. (Water boiling point = 100 °C)
🌡️ Latent Heat
- Latent heat is the heat energy absorbed or released during a change of state at constant temperature.
- Latent heat of fusion: Heat absorbed to change 1 kg of a solid to liquid at its melting point. For ice: 336,000 J/kg.
- Latent heat of vaporisation: Heat absorbed to change 1 kg of a liquid to gas at its boiling point. For water: 2,260,000 J/kg.
- During a change of state, the temperature does not change — all the heat goes into changing the state.
Why does sweating cool us? When sweat evaporates from the skin, it absorbs latent heat of vaporisation from our body, thereby cooling us.
⚙️ Effect of Temperature and Pressure on States
Effect of Temperature
- Increasing temperature provides energy to particles — they move faster, break free from forces of attraction, and the substance changes state (solid → liquid → gas).
- Decreasing temperature removes energy — particles slow down and come closer (gas → liquid → solid).
Effect of Pressure
- Increasing pressure on a gas compresses it and may cause it to liquefy (e.g. LPG in cylinders is liquefied under high pressure).
- Increasing pressure on ice lowers its melting point slightly (why ice skating works).
Evaporation vs Boiling
| Evaporation | Boiling |
|---|---|
| Occurs at all temperatures | Occurs at a fixed temperature (boiling point) |
| Occurs only at the surface | Occurs throughout the liquid |
| Slow process | Fast process |
| Causes cooling | Does not cool the surroundings |
🏷️ Key Terms
Matter
Kinetic theory
Solid
Liquid
Gas
Melting
Solidification
Vaporisation
Condensation
Sublimation
Melting point
Boiling point
Latent heat
Evaporation
Inter-particle forces
Compressibility