Cambridge IGCSE Chemistry 1 States of Matter Exam Questions

About Cambridge IGCSE Chemistry 1 States of Matter

States of matter opens the Cambridge IGCSE Chemistry 0620 syllabus and introduces the particle model used throughout the course. You need to describe the structure and properties of solids, liquids and gases, name every change of state, and explain them using the kinetic particle theory. Heating and cooling curves, the effect of temperature and pressure on the volume of a gas, and diffusion are all included. The ideas link directly to bonding, rates of reaction and gas volume calculations in stoichiometry. Examiners like to ask you to interpret a cooling curve, explain the position of a white ring in a diffusion tube, or describe particle arrangement and motion precisely.

What you need to know

• 1.1 Properties of the states Solids have a fixed shape and volume; liquids have a fixed volume but take the shape of their container; gases have no fixed shape or volume and can be compressed. These properties come from how closely packed the particles are and how freely they move.
• 1.1 Changes of state Melting, boiling, evaporation, freezing and condensation. Melting and boiling happen at fixed temperatures for a pure substance; evaporation happens at the surface of a liquid at temperatures below its boiling point.
• 1.1 Kinetic particle theory Solid: particles closely packed in a regular arrangement, vibrating about fixed positions. Liquid: closely packed but irregular, moving around each other. Gas: far apart, randomly arranged, moving quickly in all directions.
• 1.1 Heating and cooling curves Flat sections show a change of state, where energy is used to overcome the forces between particles instead of raising the temperature. Sloping sections show a single state being heated or cooled.
• 1.1 Gases (Supplement) Increasing temperature makes gas particles move faster and collide with the walls harder and more often, so the volume increases at constant pressure. Increasing pressure pushes the particles closer together, so the volume decreases.
• 1.2 Diffusion Diffusion is the net movement of particles from a region of higher concentration to lower concentration because of their random motion. It happens in gases and liquids. Extended candidates must explain that gases with a lower relative molecular mass diffuse faster.

Common mistakes in 1 States of Matter

• Saying particles in a solid do not move. They vibrate about fixed positions.
• Saying particles expand or melt when heated. The particles themselves stay the same size; they move faster and further apart.
• Confusing evaporation with boiling. Evaporation occurs only at the surface and below the boiling point; boiling occurs throughout the liquid at the boiling point.
• Describing the temperature as rising during a change of state. On a heating curve the temperature stays constant while the substance melts or boils.
• Placing the white ring of ammonium chloride in the middle of the diffusion tube. It forms nearer the hydrochloric acid end because ammonia has a lower Mr and diffuses faster.

Try three 1 States of Matter exam-style questions