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What is Matter?
Matter is the name scientists have given for anything that has MASS - for example, human beings are made of matter. There are three states in which matter can exist: solid, liquid or gas.
- SOLIDS have a fixed hard shape
- LIQUIDS have no fixed shape and will take the shape of any container they are put in, but the volume is fixed
- GASES have neither fixed shape nor fixed volume and will spread or diffuse indefinitely
Why do changes in state occur?
Most substances can exist in any of these three states depending on their temperature. For example water (H20) is a gas (steam) when heated above 100șC, it is a liquid at room temperature and becomes a solid (ice) when its temperature goes below 0șC, in winter for instance.
Substances can be made to change state by changing their temperature. This is done either by applying heat or by cooling.
- When a solid is changed to a liquid state we call it MELTING
- When a liquid is changed to a gas we call it BOILING or VAPOURISING
- When a gas is changed to a liquid we call it CONDENSING
- When a liquid is changed to a solid we call it SOLIDIFYING or FREEZING
What happens when these changes occur?
Substances are made of molecules. In a solid the molecules are packed tightly together, in a liquid the molecules move around more energetically and in a gas there is a lot of space between molecules and they flow around freely. When a substance is heated the molecules start to move around more, they take up more space and the substance expands. It is not the molecules themselves that get bigger, but the room they need to move around. The heat that is applied provides the molecules with the energy they need to increase their movement.
In the same way, if things are cooled energy is extracted as heat, and the substance will change from gas to liquid to solid. A good example of this occurring naturally is steam condensing as water on a cold surface in a bathroom. The warm steam meets the cold mirror surface, which conducts the heat of the steam away and water droplets are formed. a good example of this happening mechanically (by artificial means) is a refrigeration system - your fridge.
