1.1

Solids, liquids and gases

Cambridge IGCSE Chemistry (0620)  · Unit 1: States of matter  · 19 flashcards

Solids, liquids and gases is topic 1.1 in the Cambridge IGCSE Chemistry (0620) syllabus , positioned in Unit 1 — States of matter , alongside Particle theory.  In one line: Particles in a solid are closely packed in a regular arrangement. They vibrate about fixed positions, with limited movement and low kinetic energy.

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 confirm this is a high-yield topic: Cambridge has set undefined questions worth 687 marks here (about 10.9% of all Chemistry marks across those years).

The deck below contains 19 flashcards — 7 definitions and 12 key concepts — covering the precise wording mark schemes reward.  Use the 7 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.

Key definition

Describe the particle arrangement and motion in a solid

Particles in a solid are closely packed in a regular arrangement. They vibrate about fixed positions, with limited movement and low kinetic energy.

Example: Iron atoms in a block of iron.

What the Cambridge 0620 syllabus says

Official 2026-2028 spec

These 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.

  1. State State the distinguishing properties of solids, liquids and gases
  2. Describe Describe the structures of solids, liquids and gases in terms of particle separation, arrangement and motion
  3. Describe Describe changes of state in terms of melting, boiling, evaporating, freezing and condensing
  4. Describe Describe the effects of temperature and pressure on the volume of a gas
  5. Explain Explain changes of state in terms of kinetic particle theory, including the interpretation of heating and cooling curves Supplement
  6. Explain Explain, in terms of kinetic particle theory, the effects of temperature and pressure on the volume of a gas Supplement
Definition Flip

Describe the particle arrangement and motion in a solid.

Answer Flip

Particles in a solid are closely packed in a regular arrangement. They vibrate about fixed positions, with limited movement and low kinetic energy.

Example: Iron atoms in a block of iron.
Definition Flip

Describe the particle arrangement and motion in a liquid.

Answer Flip

Particles in a liquid are close together but not in a regular arrangement. They can move and slide past each other, with higher kinetic energy than solids.

Example: Water molecules in a glass of water.
Definition Flip

Describe the particle arrangement and motion in a gas.

Answer Flip

Particles in a gas are widely separated and randomly arranged. They move rapidly and randomly in all directions, with high kinetic energy.

Example: Oxygen molecules in the air.
Key Concept Flip

What happens to particle kinetic energy during melting?

Answer Flip

During melting, particles gain kinetic energy, allowing them to overcome the forces holding them in a fixed position in the solid.

Example: Ice (solid water) gaining energy to become liquid water.
Key Concept Flip

What happens to particle kinetic energy during boiling?

Answer Flip

During boiling, particles gain sufficient kinetic energy to overcome all intermolecular forces, allowing them to escape into the gaseous state.

Example: Liquid water gaining energy to become steam (gaseous water).
Key Concept Flip

Explain evaporation in terms of kinetic particle theory.

Answer Flip

Evaporation occurs when particles at the surface of a liquid gain enough kinetic energy to overcome the intermolecular forces and escape into the gas phase. This happens at temperatures below the boiling point.

Example: Water evaporating from a puddle.
Key Concept Flip

Describe the effect of increasing temperature on the volume of a gas, assuming pressure is constant.

Answer Flip

Increasing the temperature of a gas increases the kinetic energy of the particles, causing them to move faster and collide more frequently and forcefully with the walls of the container, increasing the volume.

Example: Heating a balloon will make it expand.
Key Concept Flip

Describe the effect of increasing pressure on the volume of a gas, assuming temperature is constant.

Answer Flip

Increasing the pressure on a gas forces the particles closer together, decreasing the volume. The particles have less space to move around.

Example: Compressing air in a syringe reduces its volume.
Definition Flip

What is condensation?

Answer Flip

Condensation is the change of state from a gas to a liquid. This happens when the gas loses energy and the particles slow down enough for intermolecular forces to form.

Example: Water vapor turning into liquid water on a cold surface.
Definition Flip

What is freezing?

Answer Flip

Freezing is the change of state from a liquid to a solid. This happens when the liquid loses energy and the particles slow down enough for intermolecular forces to hold them in fixed positions.

Example: Liquid water turning into ice.
Definition Flip

What is a closed system?

Answer Flip

A closed system is one where matter cannot enter or leave, although energy can.

Example: A sealed container with a chemical reaction taking place inside.
Key Concept Flip

Explain melting in terms of kinetic particle theory.

Answer Flip

When a solid is heated, the particles gain kinetic energy and vibrate more vigorously. At the melting point, the particles have enough energy to overcome the forces holding them in fixed positions, allowing them to move more freely as a liquid.

Definition Flip

Define a 'physical change'. Give an example.

Answer Flip

A physical change alters the form or appearance of a substance but does not change its chemical composition. Dissolving sodium chloride (NaCl) in water is a physical change, as the NaCl remains NaCl, only dispersed within the water.

Key Concept Flip

Explain why gases can be compressed but solids and liquids cannot.

Answer Flip

Gas particles are far apart with large spaces between them, so when pressure is applied, the particles can be pushed closer together. In solids and liquids, particles are already close together with very little space between them, so they cannot be compressed further.

Key Concept Flip

Describe what happens to the particles when a liquid evaporates.

Answer Flip

During evaporation, the most energetic particles at the surface of the liquid have enough kinetic energy to overcome the attractive forces between particles and escape into the gas phase. This happens at any temperature, not just at the boiling point. The remaining liquid cools because the average kinetic energy of the remaining particles decreases.

Key Concept Flip

Explain why increasing the temperature of a gas in a sealed container increases its pressure.

Answer Flip

Increasing the temperature gives the gas particles more kinetic energy, so they move faster. The faster-moving particles hit the walls of the container more frequently and with greater force. Since pressure = force per unit area, the pressure increases. The volume stays constant because the container is sealed.

Key Concept Flip

Sketch and interpret a heating curve for water, labelling the key features.

Answer Flip

A heating curve shows temperature (y-axis) vs time (x-axis):

1. Rising section (solid): temperature increases as ice warms
2. Flat section at 0°C: melting — energy breaks bonds between particles, temperature stays constant
3. Rising section (liquid): temperature increases as water warms
4. Flat section at 100°C: boiling — energy overcomes intermolecular forces, temperature stays constant
5. Rising section (gas): temperature increases as steam warms

The flat sections show state changes where energy is used to overcome forces, not to increase temperature.

Key Concept Flip

What is the difference between boiling and evaporation?

Answer Flip

Boiling occurs at a fixed temperature (the boiling point) throughout the liquid, forming bubbles of gas. Evaporation occurs at any temperature but only at the surface of the liquid. Boiling requires continuous heating; evaporation happens naturally when surface particles gain enough energy to escape.

Key Concept Flip

Explain why the temperature remains constant during a change of state.

Answer Flip

During a change of state (melting or boiling), the energy supplied is used to overcome the forces of attraction between particles rather than to increase their kinetic energy. Since temperature is a measure of the average kinetic energy of particles, the temperature stays constant until the state change is complete.

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1.2 Particle theory

Key Questions: Solids, liquids and gases

Describe the particle arrangement and motion in a solid.

Particles in a solid are closely packed in a regular arrangement. They vibrate about fixed positions, with limited movement and low kinetic energy.

Example: Iron atoms in a block of iron.
Describe the particle arrangement and motion in a liquid.

Particles in a liquid are close together but not in a regular arrangement. They can move and slide past each other, with higher kinetic energy than solids.

Example: Water molecules in a glass of water.
Describe the particle arrangement and motion in a gas.

Particles in a gas are widely separated and randomly arranged. They move rapidly and randomly in all directions, with high kinetic energy.

Example: Oxygen molecules in the air.
What is condensation?

Condensation is the change of state from a gas to a liquid. This happens when the gas loses energy and the particles slow down enough for intermolecular forces to form.

Example: Water vapor turning into liquid water on a cold surface.
What is freezing?

Freezing is the change of state from a liquid to a solid. This happens when the liquid loses energy and the particles slow down enough for intermolecular forces to hold them in fixed positions.

Example: Liquid water turning into ice.

Tips to avoid common mistakes in Solids, liquids and gases

More topics in Unit 1 — States of matter

Solids, liquids and gases sits alongside these Chemistry decks in the same syllabus unit. Each uses the same spaced-repetition system, so progress in one informs the next.

1.2 Particle theory

9 flashcards

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.

solid liquid gas state of matter particle arrangement movement kinetic theory diffusion Brownian motion melting boiling freezing condensation evaporation sublimation

Key terms covered in this Solids, liquids and gases 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.

Describe the particle arrangement and motion in a solid
Describe the particle arrangement and motion in a liquid
Describe the particle arrangement and motion in a gas
Condensation
Freezing
Closed system
A 'physical change'. Give an example

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