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| Question | Answer |
| How can most physical changes be understood? | By using the particle model. |
| What is the particle model? | The particle model is a simple representation of solids, liquids and gases. |
| What does the particle model assume? | The particle model assumes that all forms of matter are made up of invisible particles that are: -hard and incompressible -attracted to each other -constantly moving |
| How are the particles in solids? | In solids, the attraction between particles binds them tightly together. For this reason, solids are incompressible and hold their shape. |
| How are the particles in liquids? | In liquids, the particles are also packed tightly together, which makes liquids incompressible. |
| How are the particles in gases? | In gases, the particles are not stuck to each other at all and there are large spaces between gas particles which makes them highly compressible. |
| How can the physical changes of expansion and contraction be understood? | The physical changes of expansion and contraction can be understood by looking at how the motion of particles changes with temperature. |
| As the temperature increases what else happens? | As the temperature increases, so do the vibrations of the particles. |
| What happens if the vibration increases? | It pushes the particles further apart, causing the solid to expand. |
| What happens when a solid is cooled? | The particles vibrate less, allowing them to be packed more tightly and the solid contracts. |
| What is the difference between the particles in solids and liquids? | In liquids the particles are free to move, so liquids tend to expand and contract more than solids. |
| What happens when the temperature of a gas is increased? | When the temperature of a gas is increased, the particles travel faster. |
| What happens if the particles travel faster? | They hit the sides of their container more frequently and with more force. |
| What happens if a gas is cooled? | If a gas is cooled, the particles travel slower and hit the sides of their container less frequently and with less force. |
| How does the particle model explain changes of state? | The particle model explains the changes of state by looking at the relationship between how the particles move and the attraction between them. |
| What is freezing? | Freezing is the opposite of melting. As the free-moving particles in the liquid are cooled, they become less energetic, and eventually the attraction between the particles is able to fix them in position, forming a solid. |
| When does evaporation occur? | Evaporation occurs when particles in a liquid escape from the surface of the liquid to form a gas. |
| What is condensation? | When a gas is cooled and the particles move slower until the forces of attraction between the particles can hold and stick them together to form liquid droplets. |
| When are mixtures formed? | Mixtures are formed when two or more pure substances are mixed together. |
| What is diffusion? | Diffusion is a process where two liquids or two gases mix due to the motion of their particles. |
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