Practice questions · States of matter

Same particles, three arrangements.

Six original Cambridge-style questions on the particle picture of solids, liquids and gases, the properties that follow, and why a gas can be squashed but a liquid cannot.

Original questions All questions on this page are original work, written in the Cambridge IGCSE style. They are not from past papers. They test the same concepts and skills the syllabus rewards.

Answer everything from the particle picture

Spacing, arrangement, motion.

Solid: very close, regular, vibrate in place. Fixed shape and volume.
Liquid: close, random, move past each other. Fixed volume, takes the shape of its container.
Gas: far apart, fast and random. Fills the container, easily compressed.

[3 marks]

Describe the arrangement and motion of the particles in:

(a) a solid, [1] (b) a liquid, [1] (c) a gas. [1]

(a) Solid: particles in a fixed, regular, closely packed pattern, vibrating about fixed positions. ✓

(b) Liquid: particles close together but irregularly arranged, able to move past one another. ✓

[3 marks]

State whether each property describes a solid, a liquid, or a gas:

(a) has a fixed shape and a fixed volume, [1] (b) has a fixed volume but takes the shape of its container, [1] (c) spreads out to fill any container it is put in. [1]

(a) Solid. ✓

(b) Liquid. ✓

Analysis

[2 marks]

Explain, in terms of particles, why a gas can be compressed into a much smaller volume but a solid cannot.

In a gas the particles are far apart with large spaces between them, so they can be pushed closer together. ✓
In a solid the particles are already touching with no spare space, so it cannot be compressed. ✓

Analysis

[2 marks]

A solid keeps its own shape, but a liquid flows and takes the shape of its container. Explain this difference in terms of the particles.

In a solid the particles are held in fixed positions by strong forces and can only vibrate, so the shape is fixed. ✓
In a liquid the particles can move past one another, so the liquid can flow and take the shape of its container. ✓

Analysis

[2 marks]

When ice melts to water and then boils to steam, a student claims the water particles themselves change. Explain what actually changes and what stays the same.

The particles themselves do not change, they are the same water particles throughout. ✓
What changes is their arrangement, spacing, and how freely they move. ✓

Analysis

[2 marks]

A small amount of gas is released into a large empty sealed room. Explain, in terms of particle motion, why the gas spreads out to fill the whole room.

The gas particles move quickly in random directions. ✓
They travel until they collide with the walls or each other, spreading out until they are evenly distributed throughout the whole room. ✓

Mark this once you have attempted all six and checked your working. It records a Practiced badge on the topic and adds a one-time bonus. Revealing the solutions alone does not count.