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✏️ P3/P4 · PSLE Worksheet

States of Matter — Practice Worksheet

Solids, liquids, gases — particle behaviour, changes of state, and Singapore exam-style questions. Works with or without printing!

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📚
Syllabus
P3/P4 · PSLE
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Questions
30+ questions
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Includes
MCQ, T/F, OE
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Answers
Included
📖 Quick Revision

Key Concepts at a Glance

All matter is made of tiny particles. The state of matter depends on how particles are arranged and how much energy they have.

Solid
Particles tightly packed in a regular pattern. Vibrate but stay in fixed positions. Definite shape AND volume.
Liquid
Particles close but in irregular arrangement. Can slide past each other. No fixed shape — takes container's shape. Fixed volume.
Gas
Particles very far apart, move rapidly in all directions. No fixed shape OR volume — fills any container completely.
Change of StateDirectionEnergy ChangeSingapore Example
MeltingSolid → LiquidHeat addedIce kachang melting in the sun
FreezingLiquid → SolidHeat removedWater in ice cube tray in freezer
EvaporationLiquid → GasHeat added (surface only)Puddle on road drying after rain
BoilingLiquid → GasHeat added (throughout)Water boiling in a pot of mee rebus
CondensationGas → LiquidHeat removedWater droplets on cold drink can
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PSLE Exam Trap
During a change of state (e.g. ice melting at 0°C), the temperature stays CONSTANT — all energy goes into breaking bonds between particles, NOT into raising temperature. This is frequently tested in open-ended questions!
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Singapore context: Humidity is high because water evaporates rapidly from the sea and wet ground. When warm moist air hits a cold air-conditioned surface (like an MRT window), condensation forms droplets — that is the gas (water vapour in air) turning back into liquid.
✏️ Section A

Fill in the Blanks

Word Bank: particles · solid · liquid · gas · melting · freezing · evaporation · condensation · fixed · volume · flow · compressed

1. All matter is made up of tiny that are too small to see.

2. A has a definite shape and volume because its particles are locked in fixed positions — like a rock, an HDB block, or a metal coin.

3. A liquid does not have a shape — it takes the shape of its container. This is why water poured into a bowl takes the shape of the bowl.

4. Unlike solids and liquids, a can be easily into a smaller space because its particles are very far apart.

5. The change of state from solid to liquid is called . For water, this happens at 0°C.

6. The change of state from liquid to solid is called .

7. When liquid water on the ground changes to water vapour, this is called . It can happen at any temperature.

8. Water droplets forming on the outside of a cold drink can happen because of — water vapour in the air cools and turns to liquid.

9. Liquids and gases can both from one place to another — this is why liquids can be poured and gases spread out.

10. A gas has no fixed — it expands to fill any container it is placed in.

✅ Section B

True or False

Tap T or F for each statement. Then reveal the answers.

1. Solids can be easily compressed because their particles are far apart.
2. Water boils at 100°C at normal atmospheric pressure.
3. During evaporation, only particles at the surface of a liquid escape into the gas state.
4. A gas always has a fixed volume inside any container.
5. When ice melts, the temperature stays at 0°C until all the ice has melted.
6. Liquids take the shape of their container but keep the same volume.
7. Condensation happens when a gas is cooled and turns into a liquid.
8. All substances melt and boil at exactly the same temperature.
Answers: 1-F · 2-T · 3-T · 4-F · 5-T · 6-T · 7-T · 8-F
🎯 Section C

Multiple Choice Questions (MCQ)

1. Which of the following best describes the particles in a liquid?

✓ B — Liquid particles are close but irregularly arranged and can flow past each other. This is why liquids take the shape of their container.

2. A student takes a cold drink out of the fridge in Singapore's humid weather. Droplets of water appear on the outside of the can. What is this process called?

✓ C — Condensation. The warm humid Singapore air contains water vapour (gas). When it touches the cold can, it loses heat energy and turns into liquid water droplets.

3. A scientist heats a block of ice at a steady rate. The temperature stays at 0°C for several minutes before rising again. What is the BEST explanation?

✓ C — During a change of state, temperature stays constant. Energy goes into breaking the bonds between particles (changing state), not raising the temperature.

4. Which property is the SAME for both liquids and gases, but different from solids?

✓ B — Both liquids AND gases can flow. Solids cannot flow. Gases can also be compressed (unlike liquids and solids). Only liquids have fixed volume but no fixed shape.

5. Wet clothes dry faster on a windy day than on a calm day. Which statement BEST explains this?

✓ B — Wind carries away water vapour from the surface of the clothes. This creates a lower concentration of water vapour near the surface, so more liquid water evaporates to replace it. The rate of evaporation increases.
🔄 Section D

Changes of State — Match & Identify

For each scenario below, name the change of state and whether heat is added or removed.

Scenario (Singapore context)Change of StateHeat Added or Removed?
Ice in a cold drink melts on a hot dayMelting (Solid → Liquid)Added (from surroundings)
Sweat on your skin disappears on a windy dayEvaporation (Liquid → Gas)Added (from your skin — this is why you feel cool!)
Water droplets appear on MRT window when cold air meets warm outside airCondensation (Gas → Liquid)Removed
Water in the freezer turns to ice overnightFreezing (Liquid → Solid)Removed (freezer takes heat away)
Water in a pot boils when cooking at 100°CBoiling (Liquid → Gas)Added
📝 Section E

Open-Ended Questions (PSLE Style)

Q1. [2 marks] Explain why a gas can be compressed into a smaller space but a solid cannot.

Model Answer
In a gas, the particles are very far apart from each other with large empty spaces between them. When the gas is compressed, the particles are simply pushed closer together into those empty spaces — the particles themselves do not change size.

In a solid, the particles are already packed very tightly together with almost no empty spaces between them. There is no room to push the particles any closer, so the solid cannot be compressed.

Q2. [2 marks] After coming out of a swimming pool in Singapore on a breezy day, you feel cold even though the air temperature is 32°C. Use your knowledge of evaporation to explain why.

Model Answer
Water on your skin evaporates — it changes from liquid into gas (water vapour). During evaporation, only the fastest-moving, highest-energy particles escape from the surface of the liquid into the air.

This means the remaining water (and your skin) loses energy, causing its temperature to drop. You feel cold because heat energy is being taken away from your skin during evaporation. The breeze speeds this up by removing water vapour quickly, allowing more evaporation to occur.

Q3. [3 marks] A student investigates which liquid evaporates fastest: water or rubbing alcohol. She places the same volume of each on separate watch glasses in the same location and records how long each takes to fully evaporate. (a) State the variable she is changing. (b) State TWO variables she must keep the same. (c) What result would you predict, and why?

Model Answer
(a) The variable she is changing (independent variable): the type of liquid (water or rubbing alcohol).

(b) Two variables she must keep the same (controlled variables): the volume of liquid used; the location/temperature/wind conditions; the size and shape of the watch glass. (Any 2 valid.)

(c) Rubbing alcohol would evaporate faster than water because alcohol molecules have weaker bonds between them and require less energy to escape from the liquid surface into the gas state. Its boiling point is lower than water's (78°C vs 100°C), indicating it evaporates more readily at room temperature.

Q4. [Extended — PSLE OE style] [3 marks] A refrigerator keeps food cold. Inside the refrigerator, a special liquid (refrigerant) evaporates in the cooling coils. The refrigerant vapour is then pumped outside and condensed back into liquid. Explain how this process keeps the inside of the refrigerator cold. Use the words evaporation, heat, and condensation in your answer.

Model Answer
When the refrigerant evaporates inside the cooling coils, it absorbs heat energy from the air and food inside the refrigerator. This takes heat away from the inside of the fridge, making it colder.

The refrigerant vapour is then pumped outside where it undergoes condensation — it changes from gas back into liquid by releasing the heat it absorbed to the surroundings (the air outside the fridge). The liquid refrigerant is then pumped back inside to evaporate again, continuing the cycle.

So evaporation inside the fridge removes heat (keeping it cold), and condensation outside releases that heat into the room.
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