# Solids, Liquids and Gases: Particle Theory and Pressure in Gases

## Solids, Liquids and Gases: Particle Theory and Pressure in Gases

Topic: Solids, Liquids, and Gases: Particle Theory and Pressure in Gases

• Understand that all substances are made of small particles, which are in continuous motion. In solids, they vibrate in fixed positions. In liquids, they can move freely around each other. In gases, they move rapidly in all directions.

• Comprehend that heating a substance increases the energy of its particles. This leads to an increase in the speed of gas particles and an increase in the distance between particles in a liquid or solid, causing the substance to expand.

• Know the three states of matter: solid, liquid, gas. Each has unique properties. Solids have a fixed shape and volume, liquids adopt the shape of their container but have a fixed volume, gases adopt the shape and volume of their container.

• A change of state, like melting, freezing, evaporating, or condensing, involves energy being transferred without changing the temperature.

• Recognize that atmospheric pressure is caused by air molecules colliding with surfaces. The pressure of a gas in a sealed container is due to the molecules colliding with the walls of the container.

• Understand the relationship between pressure and volume of a confined gas at constant temperature (Boyle’s Law). If the volume increases, the pressure decreases, and vice versa.

• Realize that an increase in temperature increases the pressure of a gas in a sealed container. This is due to an increase in the speed and frequency of collisions between gas molecules and the container.

• Comprehend that Brownian motion is the random movement of particles in a fluid (liquid or gas), as a result of continuous collisions with other fast-moving molecules. This provides evidence for the kinetic theory of matter.

• Be aware that melting and boiling points are indicative of the strength of forces between particles of a substance. The stronger the forces, the higher the melting and boiling points.

• Explore the concept of density, defined as mass per unit volume. Solids are generally denser than liquids, and liquids denser than gases.

Also arrange your revision in a mixture of ways: diagrams, flashcards, revision guides, and practise questions. This approach can also lead to more effective retention of information.