Everything around you is made of particles far too small to see. How tightly they are packed, and how fast they move, decides whether you have a solid, a liquid or a gas.
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The same substance can be solid, liquid or gas. Only the arrangement and movement of its particles changes.
🧊 Comparing the three states
| SOLID | LIQUID | GAS | |
|---|---|---|---|
| Particles | packed tightly | close but able to slide | far apart |
| Movement | vibrate in place | move around each other | move fast and freely |
| Shape | fixed | takes the container | fills the container |
| Volume | fixed | fixed | not fixed |
| Compressible | almost not at all | very little | easily |
Why a gas can be compressed but a liquid cannot. In a gas the particles are far apart with plenty of empty space between them, so they can be pushed closer. In a liquid they are already touching, so there is almost nowhere left to go.
Particles are always moving, so they spread out on their own. That spreading is diffusion.
Diffusion is fastest in gases, slower in liquids and almost non-existent in solids — because that is the order of how freely the particles can move. Incense smells across a room within seconds; a drop of ink takes minutes to colour still water.
Heat speeds diffusion up. Warmer particles move faster, so tea leaves colour hot water far more quickly than cold. This is a favourite experiment question.
Add heat and particles move faster and spread apart. Take heat away and they slow and settle.
🔄 The names to know
| Change | From → To | Everyday example |
|---|---|---|
| Melting | solid → liquid | ice to water |
| Freezing | liquid → solid | water to ice |
| Evaporation | liquid → gas (slow, any temperature) | wet clothes drying |
| Boiling | liquid → gas (fast, at one temperature) | water at 100 °C |
| Condensation | gas → liquid | dew on a cold bottle |
| Sublimation | solid → gas directly | camphor, naphthalene balls, dry ice |
Evaporation and boiling are not the same. Evaporation happens slowly, from the surface only, at any temperature. Boiling happens throughout the liquid, quickly, at one fixed temperature. Wet clothes dry by evaporation, not boiling.
Sublimation skips the liquid stage. A naphthalene ball in a cupboard simply shrinks away without ever becoming wet. Camphor and dry ice do the same.
12 questions on particles and states of matter. 🍀
