Chapter 1: States of matter — Part 1

01 The three states of matter

Matter exists in three states: solid, liquid, and gas. These states are distinguished by the arrangement, separation, and motion of their particles, which determines their physical properties.

Solid

Particles are closely packed in a fixed, regular arrangement (lattice). They possess the least amount of energy and only vibrate in fixed positions. Because the particles are touching with no space between them, solids cannot be compressed and have a fixed shape and volume.

Liquid

Particles are close together but have a random arrangement. They possess more energy than solids and are able to move past each other, allowing liquids to flow and take the shape of their container. Like solids, the particles are still touching, so they cannot be compressed.

Gas

Particles are spread far apart and have a random arrangement. They possess the most energy and move randomly in all directions at high speeds. Because of the large spaces between particles, gases can be compressed and will expand to fill any container.

02 Particle diagrams

Structures can be described in terms of the arrangement and separation of particles in each state.

03 Kinetic particle theory and changes of state

Changes of state are physical changes because they involve overcoming or forming the forces between particles without changing the chemical composition of the substance. According to kinetic particle theory, heating a substance increases the kinetic energy of its particles, causing them to move faster.

Melting

As a solid is heated, particles vibrate more violently until they gain enough energy to overcome the attractive forces holding them in a fixed lattice, turning into a liquid.

Boiling

This occurs at a specific temperature (the boiling point). Bubbles of gas form throughout the liquid and rise to the surface to escape.

Evaporation

This occurs at the surface of the liquid only and can happen at temperatures below the boiling point.

Condensation

As a gas cools, particles lose kinetic energy and move slower, allowing attractive forces to pull them together into a liquid.

Freezing

Further cooling of a liquid causes particles to lose enough energy to be locked into a fixed, regular arrangement as a solid.

Sublimation

A direct transition from a solid to a gas (or vice versa), skipping the liquid phase entirely.

04 Heating and cooling curves

When a substance changes state, its temperature remains constant despite the continued addition or removal of thermal energy. On a graph of temperature against time, these periods appear as horizontal plateaus.

During melting and boiling

The energy added is used to break the attractive forces between particles rather than increasing their kinetic energy (temperature).

During condensing and freezing

The energy released comes from the formation of forces between particles, keeping the temperature steady.

05 Effects of temperature and pressure on gas volume

The volume of a gas is highly sensitive to changes in its environment, which can be explained by kinetic particle theory:

Temperature

Increasing the temperature increases the kinetic energy of gas particles. They move faster and collide with the walls of their container more frequently and with more force. If the container is flexible, this causes the volume to increase.

Pressure

Increasing the pressure on a gas forces the particles closer together. Because there is so much empty space between gas particles, this results in a decrease in volume.