CDS Chemistry · Matter and Its States
States of Matter and Evaporation
What the particle picture of matter says, the five states including plasma and the Bose-Einstein condensate, the two liquid elements, and what does and does not change the rate of evaporation.
Why this matters
Six CDS questions, five of them from 2019 and 2020. Two are on evaporation and turn on one idea: evaporation happens only at the surface.
Concept 1 of 2: Particles of matter and the five states
Definition
The particle picture and the states:
- Particles of matter are always moving, so they intermix on their own (diffusion).
- Particles attract each other; the force is strongest in solids, weaker in liquids, weakest in gases.
- Solid, liquid, gas, then plasma (the fourth state, ionised gas) and the Bose-Einstein condensate (the fifth state, a gas of bosons cooled almost to absolute zero).
- Only two elements are liquid at room temperature: bromine and mercury. Gallium and caesium melt just above it.
- Hydrogen, nitrogen, oxygen and carbon dioxide are all gases at room temperature; CO₂ is triatomic, not diatomic.
| State | How particles behave | Example |
|---|---|---|
| Solid | Fixed places, strong attraction | Ice, iron |
| Liquid | Move past each other, moderate attraction | Water; bromine and mercury among elements |
| Gas | Move freely, weak attraction | Hydrogen, nitrogen, oxygen, carbon dioxide |
| Plasma (4th state) | Ionised: free electrons and ions | Lightning, the Sun |
| Bose-Einstein condensate (5th state) | Atoms near absolute zero share one quantum state | Made in laboratoriesQ |
Practice this conceptself-check · 4 quick reps
The same idea in a real exam question:
Example 1 · Matter and Its States · States of Matter, Phase Changes and Diffusion
Fluorine is a gas, rubidium a solid
Plasma is the fourth state, BEC the fifth
Concept 2 of 2: What changes the rate of evaporation
Definition
The factors:
- Surface area up → faster.
- Temperature up → faster.
- Wind speed up → faster (it carries the vapour away).
- Humidity up → slower (the air already holds vapour).
- The mass of liquid does not affect the rate; it only decides how long evaporation lasts.
- Evaporation cools the liquid left behind.
Practice this concept3 quick reps
The same idea in a real exam question:
Example 2 · Matter and Its States · States of Matter, Phase Changes and Diffusion
More liquid does not mean faster evaporation
Humidity slows evaporation
Summary — formulas & gotchas at a glance
A revision cheat-sheet for the formulas and gotchas above. Click any concept name to jump back to its full explanation.
Reference tables (2)
Particles of matter and the five states5 rows
| State | How particles behave | Example |
|---|---|---|
| Solid | Fixed places, strong attraction | Ice, iron |
| Liquid | Move past each other, moderate attraction | Water; bromine and mercury among elements |
| Gas | Move freely, weak attraction | Hydrogen, nitrogen, oxygen, carbon dioxide |
| Plasma (4th state) | Ionised: free electrons and ions | Lightning, the Sun |
| Bose-Einstein condensate (5th state) | Atoms near absolute zero share one quantum state | Made in laboratoriesQ |
Watch out for (4)
- Fluorine is a gas, rubidium a solid→ Particles of matter and the five states
- Plasma is the fourth state, BEC the fifth→ Particles of matter and the five states
- More liquid does not mean faster evaporation→ What changes the rate of evaporation
- Humidity slows evaporation→ What changes the rate of evaporation
Test yourself on a real paper
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