Physics 0625 · syllabus 2.1
Cambridge IGCSE Physics 0625 — Kinetic particle model of matter topical past papers
Solids, liquids and gases explained by particles, changes of state, Brownian motion, gas pressure from collisions, absolute zero and kelvin, and pV = constant.
- Questions
- 1,345
- Years
- 2009–2026
- With mark scheme
- 99%
- Questions 2022–2026
- 486
Anyone can browse these pages. Opening the questions and their mark schemes takes a free Momentum account.
What Kinetic particle model of matter covers
The kinetic particle model explains how solids, liquids and gases behave. In a solid the particles are packed closely in a regular pattern and vibrate about fixed positions, so a solid keeps its shape and volume. In a liquid they are still close together but arranged irregularly and able to slide past one another, so a liquid flows and takes the shape of its container while keeping its volume. In a gas they are far apart and move quickly and randomly, so a gas spreads to fill any container and is easy to compress. Melting, boiling, evaporation, condensation and solidification are the changes between these states.
The hotter a substance, the faster its particles move. Nothing can be colder than absolute zero, −273 °C or 0 K, where the particles would have the least kinetic energy they can have; a temperature in kelvin is the Celsius temperature plus 273. A gas presses on its container because its particles keep colliding with the walls. Heating a fixed mass of gas in a fixed volume makes the particles move faster, so they hit the walls harder and more often and the pressure rises; squeezing the same gas into a smaller volume at a constant temperature also raises the pressure, because the particles hit each part of the walls more often.
The evidence for moving particles is Brownian motion: smoke particles in air, seen through a microscope, jiggle about at random because the much smaller air molecules, far too small to see, strike them unevenly from all sides. Extended candidates explain gas pressure as the force per unit area produced by particles colliding with a surface, link the properties of each state to the forces and distances between its particles, and use pV = constant for a fixed mass of gas kept at a steady temperature, sketching the curve it gives, on which doubling the pressure halves the volume.
In the syllabus
The headings this topic has in the Cambridge International 2026–2028 syllabus, as the board prints them.
- 2.1 Kinetic particle model of matter
What you should be able to do
- Describe how the particles in solids, liquids and gases are arranged, how far apart they are and how they move, and draw a particle diagram of each
- Name the changes of state between solids, liquids and gases
- Convert temperatures between degrees Celsius and kelvin, and explain absolute zero in terms of particle motion
- Explain gas pressure, and how it changes with temperature and with volume, in terms of particle collisions
- Describe Brownian motion and explain what it shows about the particles of a gas or liquid
- Use pV = constant for a fixed mass of gas kept at a steady temperature, and sketch the p–V graph (Extended)
Key ideas
- Solid: close, regular, vibrating; liquid: close, irregular, sliding past each other; gas: far apart, fast, random
- T (in K) = θ (in °C) + 273; absolute zero is 0 K, or −273 °C
- A higher temperature means a higher average kinetic energy of the particles
- Gas pressure is the force per unit area of particles colliding with a surface (Extended)
- For a fixed mass of gas at constant temperature, pV = constant, so p₁V₁ = p₂V₂ (Extended)
How Kinetic particle model of matter has been examined
From 2022 to 2026, Kinetic particle model of matter was on Paper 4 · Theory (Extended) in 14 of 14 exam series, worth about 16% of that paper’s marks.
| Paper | Questions | Share of marks | Series |
|---|---|---|---|
| Paper 1 · Multiple Choice (Core) | 187 | 15% | 14 of 14 |
| Paper 2 · Multiple Choice (Extended) | 180 | 14% | 14 of 14 |
| Paper 3 · Theory (Core) | 41 | 12% | 13 of 14 |
| Paper 4 · Theory (Extended) | 49 | 16% | 14 of 14 |
| Paper 6 · Alternative to Practical | 29 | 22% | 14 of 14 |
Momentum’s own count, over the questions in its bank for these years: a series is one exam session, every zone included, and a question filed under two chapters counts in both. Median marks per question: 1. The bank files this topic together with neighbouring ones, so these figures count every question in its chapters, including some on those topics.
Filed in Momentum under: Thermal Effects.
A worked example
Air sealed in a syringe takes up 60 cm³ at a pressure of 1.0 × 10⁵ Pa. The plunger is pushed in slowly, so that the temperature stays the same, until the air takes up 24 cm³. Find the new pressure, and the volume at which the pressure would be 1.5 × 10⁵ Pa.
- At constant temperature, p₁V₁ = p₂V₂
- (1.0 × 10⁵) × 60 = p₂ × 24, so p₂ = (6.0 × 10⁶) / 24 = 2.5 × 10⁵ Pa
- For 1.5 × 10⁵ Pa: V = (6.0 × 10⁶) / (1.5 × 10⁵) = 40 cm³
- Check: the smaller the volume, the larger the pressure, and pV stays at 6.0 × 10⁶ Pa cm³ throughout
Answer: 2.5 × 10⁵ Pa at 24 cm³; the pressure is 1.5 × 10⁵ Pa when the volume is 40 cm³
Written by Momentum for this page, with its own numbers; it is not taken from a past paper.
Mistakes that cost marks
- Saying the particles themselves expand or melt — the particles stay the same size; they move faster and, in solids and liquids, slightly further apart
- Explaining a rise in pressure on heating with 'more collisions' alone — the particles move faster, so they hit the walls more often and with more force each time
- Saying the air molecules are what you see in Brownian motion — the moving specks are smoke particles; the air molecules that hit them are far too small to see
- Subtracting 273 instead of adding it — 27 °C is 300 K, and a temperature in kelvin is never negative
- Using pV = constant when the temperature changes, or with the volumes in different units — it holds only at constant temperature, with p and V in the same units before and after
Exam technique
- In particle explanations, cover all three: how the particles are arranged, how far apart they are and how they move
- For gas pressure, build the chain: the particles move, collide with the walls, each collision exerts a force, and the force per unit area is the pressure
- In pV problems, write p₁V₁ = p₂V₂, substitute, and check that a smaller volume has given a larger pressure
- Draw the particles the same size in all three states, touching in solids and liquids and widely spaced in gases
Practising in Momentum
- Every question in a chapter as one list, from every paper and year in the bank, newest first or shuffled.
- Each question turns over to its own part of the mark scheme, where the board published one.
- Narrow by paper, year, session, zone and marks, and star the questions worth keeping.
- Pick chapters, a number of questions and a time, and the exam builder draws a mock to sit and mark.
Past-paper questions and mark schemes are the copyright of Cambridge International. Momentum shows them to signed-in learners for revision and does not publish them on these pages.