Particles and States of Matter Worksheet - KS3 - Intermediate

Particles and States of Matter worksheet for KS3 (Key Stage 3 / Year 7-9 (Ages 11-14)). Intermediate level science practice, aligned to the UK National Curriculum. Print-ready with answer key included.

Science•Key Stage 3 / Year 7-9 (Ages 11-14)•Particles and States of Matterintermediate

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Particles and States of Matter

Key Stage 3 • Years 7–9 • Intermediate

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Instructions: Use the particle model to explain what happens in solids, liquids and gases, and during changes of state. Read each question carefully; include scientific vocabulary and show your working where calculations are needed.

The Particle Model

Use the particle model to complete each statement. Describe particle arrangement and movement rather than changes in the substance itself.

1. In a solid, particles are arranged __________ and can only __________ about fixed positions.

2. In a liquid, particles are close together but can __________ past one another.

3. In a gas, particles are far apart and move __________ in all directions.

4. Explain why a liquid can flow but a solid keeps its shape. [3 marks]

Changes of State

Name the change of state in each situation. Then use the particle model to explain what happens to particle energy and motion during heating.

1. Solid wax becomes liquid wax. Name the change of state.

2. Liquid water becomes water vapour. Name the change of state.

3. Water vapour forms liquid droplets on a cold window. Name the change of state.

4. Explain what happens to particle energy and movement as a solid is heated until it melts. [3 marks]

Heating Data

Study the temperature readings for a pure substance as it is heated. Use the table to identify its melting and boiling points, then interpret the flat sections.

Time (min)	Temperature (°C)
0	20
2	40
4	60
6	60
8	80
10	100
12	100

1. At what temperature does melting occur?

2. At what temperature does boiling occur?

3. During which time interval is the substance boiling?

4. Why does the temperature stay constant during melting, even though energy is being supplied? [3 marks]

Diffusion in Gases

Apply the particle model to the situations below. In your explanations, refer to random particle movement and concentration where relevant.

1. A drop of perfume is released in one corner of a room. Explain how its smell can spread across the room. [3 marks]

2. In which direction do perfume particles diffuse overall: from a region of higher concentration to lower concentration, or from lower to higher concentration?

3. A gas spreads through a room more quickly when it is warmer. Explain why. [3 marks]

Explaining Gas Pressure

Use particle collisions to explain gas pressure. For the calculation, use pressure = force ÷ area and give the correct unit.

1. What causes gas particles to exert pressure on the walls of a sealed container? [3 marks]

2. A gas exerts a force of 24 N on a wall with an area of 6 m². Calculate the pressure.

3. The same gas is compressed into a smaller container at constant temperature. Explain how the pressure changes. [3 marks]

4. A sealed container of gas is heated without changing its volume. Explain why its pressure increases. [3 marks]

Answer Key

Activity 1: 1. Regularly packed; vibrate. ; 2. Move or slide. ; 3. Randomly. ; 4. Liquid particles can move past one another, allowing the liquid to flow; solid particles remain in fixed positions and only vibrate, so the solid keeps its shape.

Activity 2: 1. Melting. ; 2. Boiling (vaporisation). ; 3. Condensation. ; 4. The particles gain energy and vibrate more strongly; at the melting point, energy is used to overcome attractions between particles rather than raise the temperature; particles then move past one another as a liquid.

Activity 3: 1. 60 °C. ; 2. 100 °C. ; 3. 10–12 minutes. ; 4. Energy is used to overcome attractions between particles and change the state; it does not increase the particles’ average kinetic energy during the melting plateau, so the temperature remains constant.

Activity 4: 1. Perfume particles move randomly and diffuse from the high-concentration region near the drop into regions of lower concentration, spreading through the air. ; 2. From higher concentration to lower concentration. ; 3. At a higher temperature, gas particles have more kinetic energy and move faster, so diffusion occurs more quickly.

Activity 5: 1. Gas particles move randomly and collide with the container walls; each collision exerts a force, and the combined force per unit area produces pressure. ; 2. 24 ÷ 6 = 4 Pa. ; 3. Pressure increases: particles have less space and collide with the walls more frequently; at constant temperature their average kinetic energy does not increase. ; 4. Heating gives the particles more kinetic energy, so they move faster and collide with the walls more frequently and with greater force, increasing pressure.