Matter and Changes of State✓ Updated 2026
Matter and changes of state explained for PSLE Science. Solids, liquids, and gases, all 6 state changes, evaporation vs boiling — with Singapore examples and exam tips.
What Is Matter and What Are Its Three States?
Matter is anything that has mass and takes up space — which means everything around you is matter. Scientists classify matter into three states depending on how closely packed and how freely moving its particles are: solid, liquid, and gas. The state a substance is in depends on temperature and pressure — change either, and you can change the state.
States of Matter in Singapore's Daily Life
Add ice cubes from your freezer to a cup of teh tarik — the ice (solid) melts (solid → liquid) as it absorbs heat from the drink. The steam rising from a bowl of hot soup at a hawker centre is water evaporating (liquid → gas). If that steam hits the cold surface of an air-conditioned window, it condenses (gas → liquid) — forming tiny droplets you can see.
Your wet school uniform hanging on the bamboo pole outside your HDB flat dries because water evaporates from the fabric — even without boiling, liquid water particles at the surface gain enough energy to escape into the air as vapour.
On a humid Singapore day, a cold can of drink from the vending machine quickly becomes wet on the outside. This is not the drink leaking — it is water vapour from the surrounding air condensing on the cold surface of the can.
Dry ice (solid CO₂) sublimes directly from solid to gas without becoming liquid first — you can sometimes see this used for dramatic effects at events in Singapore. The white "smoke" is actually water vapour from the air condensing due to the cold, not the dry ice itself.
Solids, Liquids, and Gases — What's Different?
| Property | Solid | Liquid | Gas |
|---|---|---|---|
| Shape | Fixed | Takes shape of container | Takes shape of container |
| Volume | Fixed | Fixed | No fixed volume — expands to fill space |
| Particle arrangement | Closely packed, regular | Close but irregular, can flow | Far apart, random, move freely |
| Particle movement | Vibrate in place only | Slide past each other | Move freely in all directions |
| Compressible? | No | No | Yes — particles far apart |
How Matter Changes from One State to Another
- Melting (solid → liquid): Heat is absorbed. Particles gain energy and break free from their fixed positions. E.g. ice melting.
- Freezing (liquid → solid): Heat is released. Particles lose energy and lock into fixed positions. E.g. water freezing in your HDB freezer.
- Evaporation (liquid → gas): Heat is absorbed. Occurs at the surface of the liquid at any temperature. Slow process. E.g. wet clothes drying, puddles disappearing after rain.
- Condensation (gas → liquid): Heat is released. Water vapour cools and becomes liquid droplets. E.g. cold can becoming wet, morning dew on grass.
- Boiling (liquid → gas): Heat is absorbed. Occurs throughout the liquid at its boiling point (100°C for water at sea level). Fast, vigorous process.
- Sublimation (solid → gas directly): Solid converts to gas without passing through liquid. E.g. dry ice (solid CO₂), iodine crystals when heated.
The Critical Difference You Must Know
| Feature | Evaporation | Boiling |
|---|---|---|
| Where does it occur? | Surface of liquid only | Throughout the liquid (bubbles) |
| Temperature needed? | Any temperature | At boiling point (100°C for water) |
| Speed | Slow | Fast and vigorous |
| Visible bubbles? | No | Yes — bubbles of vapour form inside |
| Effect on remaining liquid | Remaining liquid gets cooler | Temperature stays at boiling point |
Why Does Evaporation Cool the Remaining Liquid?
In any liquid, particles are moving at many different speeds. During evaporation, only the fastest-moving (most energetic) particles at the surface have enough energy to escape into the air as gas. The slower, less energetic particles remain in the liquid.
When the most energetic particles leave, the average kinetic energy of the remaining particles decreases — and lower average kinetic energy means lower temperature. This is why evaporation cools the liquid left behind.
This is the principle behind sweating: your body releases sweat (water), which evaporates from your skin, carrying heat energy away and lowering your skin temperature. In Singapore's humid climate, the air is already saturated with water vapour, so sweat evaporates more slowly — which is why you feel hotter and sweatier on a humid day even if the temperature is the same.
Common Mistakes
Key Points at a Glance
- Solid: fixed shape + volume. Liquid: fixed volume only. Gas: no fixed shape or volume
- Melting and evaporation/boiling: absorb heat. Freezing and condensation: release heat
- Evaporation: surface only, any temperature, slow, cools remaining liquid
- Boiling: throughout liquid, at boiling point only, fast, temperature stays constant
- Sublimation: solid → gas directly (dry ice)
- Visible "steam" = liquid droplets (condensed), not water vapour (which is invisible)
⚔ States of Matter — Properties
Three states of matter, each with distinct properties. Know shape, volume, and particle arrangement for each.
🔄 Changes of State
Heating causes changes upward (solid to gas). Cooling reverses them. Mass is ALWAYS conserved.
Liquid → Gas = Evaporation/Boiling
Solid → Gas = Sublimation (e.g. dry ice)
Liquid → Solid = Freezing/Solidification
Gas → Solid = Deposition
🔬 Separation Methods
Example: sand from water
How: filter paper traps solid; liquid passes through
Example: salt from salt water
How: heat evaporates liquid; solid remains
Example: iron filings from sand
How: magnet attracts only magnetic material
Example: gravel from sand
How: smaller particles fall through holes in sieve
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Related PSLE Topics
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