Kinetic Particle Theory Exam Questions
Practice IGCSE Chemistry exam questions on kinetic particle theory. Covers particle motion, Brownian motion, temperature and kinetic energy, and evidence for the theory with mark schemes and examiner notes.
Published by IGCSEChemistry.com.my
Chemistry teaching team: K. S. Tan (15+ years teaching IGCSE Chemistry) and Ms Yash (10+ years teaching IGCSE Chemistry) and Ms Kartini (15+ years teaching IGCSE Chemistry).
Mapped to Cambridge IGCSE Chemistry 0620 (2026–2028). Last updated 2026-08-19.
These questions test your understanding of kinetic particle theory. Answer each one before revealing the mark scheme.
Question 1 (3 marks, Core)
A student observes smoke particles under a microscope. The smoke particles appear as bright specks that move in a jerky, random way.
(a) Describe the movement of the smoke particles. (1)
(b) Explain why the smoke particles move this way. (2)
Mark scheme
(a) The smoke particles move in random, jerky/zigzag paths [1]
(b) The smoke particles are bombarded / hit by air molecules [1] which are too small to see but are moving randomly and at high speed [1]
Examiner note: “The air pushes the smoke” is too vague. You must state that air molecules collide with the smoke particles. The randomness of the movement is because air molecules hit from different directions at different times.
Question 2 (2 marks, Core)
State the name given to the random movement of visible particles caused by collisions with invisible molecules. Explain what this observation provides evidence for.
Mark scheme
- Brownian motion [1]
- It provides evidence that gas/liquid particles are in constant random motion / evidence for kinetic particle theory [1]
Examiner note: Spelling matters — “Brownian” must have a capital B. “Brown’s motion” is not accepted.
Question 3 (3 marks, Supplement)
Use kinetic particle theory to explain what happens to a gas when it is heated in a sealed container of fixed volume.
Mark scheme
- Heating gives the gas particles more kinetic energy [1]
- The particles move faster [1]
- They collide with the walls more frequently and with greater force, so the pressure increases [1]
Examiner note: “The particles expand” is wrong — individual particles do not expand. It is the increased speed and collision rate that matters. In a fixed volume, the gas cannot expand, so pressure increases instead.
Question 4 (4 marks, Supplement)
A student inflates a balloon and places it in a freezer.
(a) Predict what will happen to the size of the balloon. (1)
(b) Use kinetic particle theory to explain your prediction. (3)
Mark scheme
(a) The balloon will get smaller / deflate partially [1]
(b) At lower temperature, the gas particles have less kinetic energy and move more slowly [1]. They hit the walls of the balloon less frequently and with less force [1]. The reduced pressure inside allows the external atmospheric pressure to push the balloon inward / the balloon contracts [1].
Examiner note: “The gas contracts” without a particle explanation scores 0. You must explain the chain: lower temperature → less KE → fewer/weaker collisions → lower pressure → balloon shrinks.
Question 5 (2 marks, Core)
State two key assumptions of kinetic particle theory.
Mark scheme
Any two from:
- All matter is made of tiny particles [1]
- Particles are in constant random motion [1]
- Particles in a gas move in straight lines between collisions [1]
- The temperature of a substance is related to the average kinetic energy of its particles [1]
Examiner note: “Particles move” is not enough — you must include “constant” and/or “random” motion to score the mark.
Question 6 (3 marks, Core)
Pollen grains scattered on the surface of water are observed under a microscope. The grains move in a random, jerky manner.
(a) Explain why the pollen grains move. (2)
(b) Predict how the movement would change if the water temperature is increased. (1)
Mark scheme
(a) Water molecules collide with / bombard the pollen grains [1]. The collisions are uneven / from random directions, causing the pollen to move in a jerky, random way [1].
(b) The pollen grains would move faster / more vigorously because the water molecules have more kinetic energy at higher temperatures and hit the pollen harder [1]
Examiner note: This is Brownian motion in a liquid rather than a gas — the same principle applies. The pollen grains are large enough to see; the water molecules are not.
Question 7 (4 marks, Supplement)
A bicycle tyre is pumped up on a cold morning (5 degC). After cycling on a hot day, the temperature of the air inside the tyre reaches 45 degC. The volume of the tyre does not change significantly.
(a) Explain, using kinetic particle theory, why the pressure inside the tyre increases. (3)
(b) Suggest why the tyre might eventually burst if cycling continues in extreme heat. (1)
Mark scheme
(a) The air particles gain kinetic energy as temperature rises [1]. They move faster and collide with the walls of the tyre more frequently [1] and with greater force, so the total force on the tyre wall increases / pressure increases [1].
(b) The pressure inside could exceed the strength of the tyre wall / exceed the pressure the tyre can withstand [1]
Examiner note: “Hot air takes up more space” is a macroscopic description, not a kinetic theory explanation. You must link temperature → kinetic energy → speed → collision frequency and force → pressure.
What to revise if you scored below 5
If you struggled with Brownian motion (Questions 1-2, 6), make sure you understand the difference between the visible particles and the invisible molecules causing the movement. If the pressure questions (3, 4, 7) were difficult, revisit the kinetic particle theory notes and practise the chain of reasoning: temperature → kinetic energy → particle speed → collision frequency and force → pressure.
Studying this yourself? Tutoring arrangements are normally made by a parent or guardian. Message us for the details to share with them, or send them this page.