States of Matter

• Three states — solid, liquid, gas; differ in shape, volume, compressibility, and particle arrangement.
• Solids — definite shape and volume; particles closely packed, vibrate in fixed positions.
• Liquids — definite volume, no definite shape; particles close but can slide.
• Gases — no definite shape or volume; particles far apart, random motion.
• Plasma and Bose–Einstein condensate — additional states (NCERT mention).

1. Solid — strong interparticle forces; incompressible; high density.
2. Liquid — moderate forces; flow; take shape of container.
3. Gas — weak forces; highly compressible; low density.
4. Diffusion — fastest in gases, slower in liquids, negligible in solids.
5. Diagram (text) — solid: regular lattice; liquid: layers sliding; gas: scattered dots.
6. NCERT Ch. 1 — compare ice, water, steam (same substance, different states).
7. Real world — LPG stored as liquid under pressure; CO₂ fire extinguisher.
8. Temperature effect — heating increases particle kinetic energy → state change.

Identifying state of water at 25 °C, 100 °C, and −10 °C at 1 atm

Step 1 — 25 °C → liquid water (room temperature).
Step 2 — 100 °C → boiling point → gas (steam/water vapour).
Step 3 — −10 °C → below freezing → solid ice.
Step 4 — Same H₂O molecules; different kinetic energy and spacing.
Conclusion: state depends on temperature and pressure.

• Thinking steam is invisible (visible 'steam' is condensed water droplets).
• Misconception: gases have no mass (they have mass and occupy space).
• Confusing melting with evaporation.
• Assuming all solids are hard (wax, butter are soft solids).
• Forgetting plasma is ionised gas (e.g. Sun).

• List three properties each of solids, liquids, and gases.
• In which state does diffusion occur fastest?
• Why can gases be compressed easily but not solids?
• Give one example of matter in each state.

Open the Practice tab for graded questions on States of Matter.