# Solids, Liquids and Gases: Temperature and Particle Theory

## Solids, Liquids and Gases: Temperature and Particle Theory

• Each substance can exist in three different states: solid, liquid, and gas.

• The state of a substance at room temperature is determined by the forces between its particles.

• Particles in a solid are closely packed in a regular pattern. They vibrate in fixed positions but do not move from place to place.

• Solid substances have a fixed shape and cannot flow.

• Particles in a liquid are in a random arrangement but are still close together.

• They can move around each other, hence liquids can flow and take the shape of their container.

• In gases, particles are far apart in a random arrangement. They move freely and have most energy among the three states of matter.

• Gases fill any container they are put in, and can be easily compressed because of the large spaces between particles.

• Temperature is a measure of the average kinetic energy of particles in a substance.

• Increasing the temperature of a substance gives the particles more energy. This can cause a substance to change state: from solid to liquid (melting), liquid to gas (evaporating/boiling) or from solid straight to gas (sublimation).

• Decreasing the temperature removes energy from the particles. This can make a substance change from gas to liquid (condensing) or from liquid to solid (freezing).

• The greater the temperature, the greater the kinetic energy of the particles and the faster they move.

• The Kelvin (K) is the SI unit for temperature, where 0K (absolute zero) is the point at which particles have minimum (but not zero) kinetic energy.

• A substance can stay at the same temperature despite energy being added when it is changing state (melting, boiling) because the energy is being used to break bonds between the particles.

• In every change of state, there is no change in the mass of a substance.

• This particle theory helps explain the different states of matter, and how substances change state with changes in temperature.