Particle theory
Cambridge IGCSE Chemistry (0620) · Unit 1: States of matter · 9 flashcards
Particle theory is topic 1.2 in the Cambridge IGCSE Chemistry (0620) syllabus , positioned in Unit 1 — States of matter , alongside Solids, liquids and gases. In one line: Diffusion is the movement of particles from an area of high concentration to an area of low concentration due to their random motion. The rate of diffusion depends on factors like temperature and particle mass; higher temperature increases motion, lower mass increases diffusion.
This topic is examined in Paper 1 (multiple-choice) and Papers 3/4 (theory), plus Paper 5 or Paper 6 (practical / alternative to practical). Past papers from 2022 to 2025 show this topic across undefined questions worth 289 marks (around 4.6% of all Chemistry marks in those years).
The deck below contains 9 flashcards — 2 definitions, 1 key concept and 6 identification cards — covering the precise wording mark schemes reward. Use the 2 definition cards to lock down command-word answers (define, state), then move on to the concept and application cards to handle explain, describe and compare questions.
Describe diffusion in terms of kinetic particle theory
Diffusion is the movement of particles from an area of high concentration to an area of low concentration due to their random motion. The rate of diffusion depends on factors like temperature and particle mass; higher temperature increases motion, lower mass increases diffusion.
What the Cambridge 0620 syllabus says
Official 2026-2028 specThese are the exact learning objectives Cambridge sets for this topic. Match the command word (Describe, Explain, State, etc.) in your answer to score full marks.
- Describe and explain Describe and explain diffusion in terms of kinetic particle theory
- Describe and explain Describe and explain the effect of relative molecular mass on the rate of diffusion of gases Supplement
Describe diffusion in terms of kinetic particle theory.
Diffusion is the movement of particles from an area of high concentration to an area of low concentration due to their random motion. The rate of diffusion depends on factors like temperature and particle mass; higher temperature increases motion, lower mass increases diffusion.
How does relative molecular mass (Mr) affect the rate of diffusion of gases?
Gases with lower relative molecular mass (Mr) diffuse faster than gases with higher Mr. Lighter particles move faster at the same temperature.
Give an example of a greenhouse gas.
Examples of greenhouse gases include carbon dioxide (CO₂), methane (CH₄), water vapor (H₂O), and nitrous oxide (N₂O).
Name a compound that reacts with acid rain.
Calcium hydroxide (lime), calcium carbonate (limestone), or calcium oxide react with acid rain, neutralizing the acidic components.
What is the purpose of a catalytic converter?
Catalytic converters are used to reduce pollution by converting harmful gases, like carbon monoxide and nitrogen oxides, into less harmful substances, such as carbon dioxide and nitrogen.
What are the products of complete combustion?
Complete combustion of hydrocarbons produces carbon dioxide (CO₂) and water (H₂O).
Name the acid catalyst used for the creation of alkenes from alcohols.
Phosphoric acid (H₃PO₄) is a common catalyst used in the dehydration of alcohols to form alkenes.
Give two examples of alcohols that could be produced from hydration of butene.
Butan-1-ol and Butan-2-ol can be produced through the hydration of butene. They are isomers of Butanol.
Which gas reduces the oxygen-carrying capacity of blood?
Carbon monoxide reduces the oxygen-carrying capacity of the blood, potentially causing breathing problems, drowsiness, headaches, sickness, or even death.
Key Questions: Particle theory
Describe diffusion in terms of kinetic particle theory.
Diffusion is the movement of particles from an area of high concentration to an area of low concentration due to their random motion. The rate of diffusion depends on factors like temperature and particle mass; higher temperature increases motion, lower mass increases diffusion.
What is the purpose of a catalytic converter?
Catalytic converters are used to reduce pollution by converting harmful gases, like carbon monoxide and nitrogen oxides, into less harmful substances, such as carbon dioxide and nitrogen.
Tips to avoid common mistakes in Particle theory
- ● Solid, liquid, and gas: learn how the assumptions of particle theory explain each state's volume, shape, and density.
- ● In your answers about particle theory, highlight particle arrangement AND the spacing between them, e.g. gases have particles far apart and randomly arranged.
- ● When describing a gas using the Kinetic Particle Theory, mention that the particles are widely separated, randomly arranged, and move randomly at high speed.
- ● For kinetic particle theory, study and compare particle separation, arrangement and motion in solids, liquids, and gases.
- ● Create a table comparing particle arrangement and motion in solids, liquids, and gases to highlight the distinctions.
More topics in Unit 1 — States of matter
Particle theory sits alongside these Chemistry decks in the same syllabus unit. Each uses the same spaced-repetition system, so progress in one informs the next.
Cambridge syllabus keywords to use in your answers
These are the official Cambridge 0620 terms tagged to this section. Mark schemes credit responses that use the exact term — weave them into your answers verbatim rather than paraphrasing.
Key terms covered in this Particle theory deck
Every term below is defined in the flashcards above. Use the list as a quick recall test before your exam — if you can't define one of these in your own words, flip back to that card.
Related Chemistry guides
Long-read articles that go beyond the deck — cover the whole subject's common mistakes, high-yield content and revision pacing.
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