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The particle model and changes of state
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Everything is made of tiny particles. How they are arranged and how they move explains solids, liquids and gases.
Solids, liquids and gases
The particle model says all matter is made of tiny particles. The difference between the states is how the particles are arranged and how they move.
Gas pressure
Gas particles hit the walls of their container. Each hit pushes on the wall. All these pushes cause gas pressure.
If you heat the gas, the particles move faster and hit harder and more often, so the pressure goes up.
If you heat the gas, the particles move faster and hit harder and more often, so the pressure goes up.
Changes of state
Melting: solid to liquid. Freezing: liquid to solid.
Boiling and evaporating: liquid to gas. Condensing: gas to liquid.
Sublimation: solid straight to gas.
Changes of state are physical changes: the particles are not changed, only rearranged, so the mass stays the same and the change can be reversed.
Pure water melts at 0 °C and boils at 100 °C.
Boiling and evaporating: liquid to gas. Condensing: gas to liquid.
Sublimation: solid straight to gas.
Changes of state are physical changes: the particles are not changed, only rearranged, so the mass stays the same and the change can be reversed.
Pure water melts at 0 °C and boils at 100 °C.
Use the particle model to explain why a gas can be squashed but a solid cannot.
- In a gas the particles are far apart, with lots of space between them.
- Squashing pushes them closer into that space.
- In a solid the particles are already touching, so there is no space.
Answer: Gas particles have big spaces between them; solid particles are already touching.
Solids: close, regular, vibrate. Liquids: close, random, move past each other. Gases: far apart, fast, random. Gas pressure comes from particles hitting walls. Changes of state are physical and keep the mass the same.
The interactive lesson includes the diagrams for this topic.
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