States of Matter and Kinetic Particle Theory: Practice Questions

These are original questions written for Marlbridge, for revision and practice on this content. They are not reproduced past-paper questions, and they do not replicate the exam’s exact structure, question count or mark tariffs — examination boards hold copyright in their own papers. Use these alongside the official past papers available free from your board.

Related: States of Matter revision notes

Tier note: questions and parts marked (0620 Extended, 5070 required) go beyond 0620 Core: explaining changes of state and heating curves in terms of kinetic particle theory (syllabus 1.1 outcome 5), explaining the effects of temperature and pressure on a gas in terms of particles (1.1 outcome 6) and the effect of relative molecular mass on the rate of diffusion (1.2 outcome 2). Everything else is 0620 Core. 5070 has no tiers, so O Level candidates need all of it.

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Section A

1. Describe the arrangement, separation and movement of particles in a solid, a liquid and a gas. [6]

2. Name the change of state for each: solid → liquid, liquid → gas, gas → liquid, liquid → solid. [4]

Section B

3. (0620 Extended, 5070 required) A student heats ice from −20 °C until it becomes steam and plots temperature against time.

(a) Explain why the temperature stays constant at 0 °C even though heat is still supplied. [3] (b) Explain why the flat section at 100 °C is longer than the one at 0 °C. [2]

4. Bromine vapour spreads to fill a gas jar.

(a) Name and define the process. [2] (b) Explain why it happens faster at higher temperature. [2] (c) (0620 Extended, 5070 required) Ammonia and hydrogen chloride are released at opposite ends of a tube. Explain why the white ring forms nearer the hydrogen chloride end. [3]

5. (0620 Extended, 5070 required) Explain, in terms of particles, why a gas exerts pressure on the walls of its container and why the pressure rises when the gas is heated at constant volume. [4]

6. (0620 Extended, 5070 required) Explain why a substance with strong forces between its particles has a high melting point. [2]

7. Explain, in terms of particle separation and arrangement, why a solid has a fixed shape and volume, a liquid has a fixed volume but no fixed shape, and a gas has neither. [3]

8. State whether diffusion occurs in solids, and explain why or why not. [2]

9. (0620 Extended, 5070 required) Explain the separate effects of (a) increasing temperature and (b) increasing pressure on the volume of a fixed mass of gas. [3]

10. A question asks a student to explain a change of state, but the student only describes what happens. Why does this lose marks? [1]

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11. Describe the arrangement and the motion of the particles in a liquid, and state one way in which the particles in a gas are different. [3]

Answers

1. Any 2 of the 3 points per state earn credit (arrangement, separation, movement — 1 mark each, capped at 2 marks per state, 6 marks total). Solid — particles are closely packed in a regular arrangement, with the smallest separation between them, vibrating about fixed positions [1] [1]. Liquid — particles are close together but randomly arranged, with a separation similar to a solid’s, able to slide past one another [1] [1]. Gas — particles are far apart and randomly arranged, with the largest separation between them, moving rapidly in all directions [1] [1].

2. Melting [1]; boiling or evaporation [1]; condensing [1]; freezing [1]. (Sublimation — solid directly to gas — is not one of the five changes of state named by 0620/5070 and would not be creditable here.)

3. (a) The energy supplied is used to overcome the forces of attraction between the particles [1] rather than to increase their kinetic energy [1]; since temperature is a measure of average kinetic energy, it stays constant during the change of state [1]. (b) Boiling requires all the remaining forces between particles to be broken so they can separate completely [1], whereas melting only loosens them enough to let particles slide — so more energy, and therefore more time, is needed [1].

4. (a) Diffusion [1] — the net movement of particles from a region of higher concentration to a region of lower concentration until evenly spread [1]. (b) The particles have more kinetic energy and move faster [1], so they spread through the container more quickly [1]. (c) Ammonia has a lower relative molecular mass (17) than hydrogen chloride (36.5) [1], so at the same temperature its molecules travel faster [1] and cover a greater distance before meeting — so the ring forms further from the ammonia end [1].

5. The gas particles are in constant random motion and collide with the walls of the container [1]; each collision exerts a small force, and the force per unit area is the pressure [1]. On heating, the particles gain kinetic energy and move faster [1], so collisions are more frequent and harder, increasing the pressure [1].

6. More energy is needed to overcome the stronger forces of attraction between the particles [1], so a higher temperature must be reached before the solid melts [1].

7. A solid has a fixed shape and volume because its particles are held in fixed positions and cannot move from them [1]. A liquid has a fixed volume but takes the shape of its container because its particles are still close together but can slide past one another [1]. A gas has neither, and can be compressed, because of the large spaces between its widely separated particles [1].

8. No [1] — solid particles are held in fixed positions and cannot move throughout the material, so there is no net movement of particles from one region to another [1].

9. (a) Increasing temperature gives particles more kinetic energy, so they move faster and collide with the container walls more frequently and with greater force [1]; if free to expand, the gas’s volume increases [1]. (b) Increasing pressure pushes the particles closer together, reducing the space between them, so the gas’s volume decreases [1]. (0620 Core, syllabus 1.1 outcome 4, needs only the direction of each effect: volume increases with temperature and decreases with pressure. The particle explanation is Extended.)

10. Describing only states what happens, while explaining requires reference to particle energy, motion and the forces between particles — an answer that merely describes when asked to explain does not earn the explanation marks [1].

11. In a liquid the particles are close together (touching) and irregularly arranged [1], and they move randomly and slide past one another [1]. In a gas the particles are far apart (or: move faster, in all directions) [1].

Examiner insight (June 2025): answers lost marks by describing the liquid itself (“it takes the shape of its container”) instead of its particles, or by getting the spacing or speed of the particles wrong. Describe individual particles. Try the real question next: Cambridge IGCSE Chemistry 0620, June 2025, Paper 32, Question 2.

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Where marks are usually lost

• Saying particles in a solid do not move — they vibrate.
• (0620 Extended, 5070 required) Explaining the flat section as “the heat is lost”.
• (0620 Extended, 5070 required) Forgetting to link molecular mass to speed of diffusion.
• (0620 Extended, 5070 required) Saying pressure is caused by particles “pushing” rather than colliding.
• Describing a change of state when the command word asks for an explanation.
• Saying diffusion happens in solids, or that particles in a solid have no energy at all.