This mini-lesson walks you through the whole of Cambridge IGCSE Chemistry Topic 1: the three states and their properties, the kinetic particle model, the changes of state and heating curves, how temperature and pressure affect a gas, and diffusion.
Work through each screen, answer the questions as you go (some are wordy, some are calculations) and collect ⭐ stars. Items marked SUPPLEMENT are extended-only. Press Start when you're ready.
Matter exists in three states. Cambridge expects you to state the distinguishing properties of each:
Watch out: both liquids and gases can flow, so we call them fluids. The big differences are that a gas has no fixed volume and is easily compressed, while a liquid is not.
Describe each state in terms of particle separation, arrangement and motion:
Common mistake: heating does not make the particles themselves get bigger. The particles stay the same size — they gain energy, move more, and the spacing between them changes.
Tap the state that best matches each particle description.
Adding or removing energy moves a substance between states. Cambridge names five changes you must describe:
Conservation of mass: changes of state are physical changes — no new substance forms and mass is conserved. Sealed ice that melts then boils has the same mass throughout; only the arrangement and energy of the particles change.
Extension note: a few solids (e.g. solid carbon dioxide, iodine) turn straight to gas — sublimation. This is useful background, but the named changes assessed in 0620 Topic 1 are the five above.
Extended only. Explain changes of state using kinetic particle theory. As you heat a solid steadily, a heating curve (temperature against time) shows two flat plateaus:
Cooling curve: run it in reverse. Plateaus appear at the freezing point (gas→liquid→solid) as particles release energy while staying at the same temperature.
Cambridge expects you to describe the effects of temperature and pressure on the volume of a gas (qualitatively):
Supplement explanation SUPPLEMENT: in terms of kinetic particle theory, gas pressure comes from particles colliding with the walls. Heating makes them move faster and hit the walls harder and more often; if the container can expand, the gas takes up more room. Pushing the walls in (more pressure) packs the particles closer, so the volume falls.
Diffusion is the spreading out of particles from a region of higher concentration to a region of lower concentration, until they are evenly mixed.
Explain it with kinetic particle theory: particles are in constant random motion. They move from where there are more of them to where there are fewer, mixing without being stirred. Diffusion is fastest in gases (particles far apart, moving fast), slower in liquids, and negligible in solids.
Why it matters: smelling perfume across a room is diffusion — the smell particles move and spread through the air all on their own.
Extended only. The rate of diffusion of a gas depends on its relative molecular mass (Mr): lighter molecules diffuse faster than heavier ones at the same temperature.
In the classic experiment, cotton wool soaked in ammonia solution (giving NH₃ gas) and concentrated hydrochloric acid (giving HCl gas) are put at opposite ends of a glass tube. Where the gases meet, a white ring of ammonium chloride (NH₄Cl) forms — and it forms closer to the HCl end.
Reasoning SUPPLEMENT: at the same temperature the gas particles have the same average kinetic energy, so the lighter NH₃ molecules move faster and cover more of the tube before meeting the slower, heavier HCl molecules.
Three states: solid (fixed shape & volume), liquid (fixed volume, takes shape), gas (no fixed shape or volume, compressible).
Particle model: spacing, arrangement & motion increase solid → liquid → gas; particles don't change size, the spacing/energy does.
Changes of state: melting, boiling, evaporating, freezing, condensing — physical changes; mass conserved.
Heating curves SUPP: plateaus at m.p. & b.p. — energy overcomes forces, not raising temperature.
Gas volume: ↑ temperature → expands; ↑ pressure → smaller volume.
Diffusion: particles spread high → low concentration; SUPP lighter molecules diffuse faster (NH₃ vs HCl).
You've covered the whole of Cambridge IGCSE Chemistry (0620) Topic 1 — States of matter, with the Supplement (extended) items flagged. Press Finish to see your score.
You've worked through States of Matter for Cambridge IGCSE Chemistry. 🎉
Your stars: 0 / 0
Next: test yourself in the Evaluate stage Confidence Quiz, then lock it in with Verify.