States of Matter
States of Matter and Diffusion
Cambridge IGCSE Chemistry
The three states
| State | Separation | Arrangement | Motion |
|---|---|---|---|
| solid | touching | regular | vibrate about fixed positions |
| liquid | touching | random | random, moving past each other |
| gas | far apart | random | random, moving quickly in all directions |
A solid has a fixed shape and a fixed volume; a liquid has a fixed volume and takes the shape of its container; a gas fills its container.
The state at a given temperature
| Temperature | State |
|---|---|
| below the melting point | solid |
| between the melting point and the boiling point | liquid |
| above the boiling point | gas |
- For a liquid, compare the temperature with both points in one answer: the melting point is below the temperature and the boiling point is above it.
- For a gas: the temperature is above the boiling point.
- With negative temperatures, the larger the number after the minus sign, the lower the temperature.
Changes of state
| Change | From | To |
|---|---|---|
| melting | solid | liquid |
| freezing | liquid | solid |
| boiling | liquid | gas |
| evaporation | liquid | gas |
| condensation | gas | liquid |
Boiling happens at a specific temperature and throughout the liquid; evaporation happens over a range of temperatures and is a surface process.
A cooling curve falls, is a horizontal line at the melting point while the liquid freezes, then falls again. Each horizontal section is a change of state.
Diffusion
- In diffusion, particles move from an area of high to low concentration because the particles move randomly.
- A smell spreads across a room by evaporation of the liquid, then diffusion of its particles.
- A gas with a lower relative molecular mass diffuses faster.
- Of several gases, the one with the lowest relative molecular mass diffuses fastest.
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