States of Matter and Kinetic Particle Theory: Practice Questions

These are original questions written for Marlbridge, in the style and at the standard of the examination. They are not reproduced past-paper questions — 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

---

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. 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) 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. 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. 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. 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]

---

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].

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].

---

Where marks are usually lost

• Saying particles in a solid do not move — they vibrate.
• Explaining the flat section as “the heat is lost”.
• Forgetting to link molecular mass to speed of diffusion.
• 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.