All matter can be found in four physical states: solid, liquid, gas, and plasma. A substance can switch from one state to another (from solid to liquid, from liquid to gas, from gas to solid, or vice versa) when exposed to changes in temperature and pressure.
These changes of state modify the volume of the substances. They tend to expand by heating and contract by cooling, without implying changes at a chemical level, but on a physical level.
The phenomena occuring when matter passes from solid to liquid and vice versa are:
- Fusion. Process in which a substance changes its state from solid to liquid by increasing its temperature. This process occurs at a certain temperature called the “melting point”, which is different for each substance. For instance: the melting point of water is 0 ° C.
- Solidification. Process by which a substance changes its state from liquid to solid. This process happens when the pressure of the liquid substance is greatly increased. For instance: water that is transformed into ice by compression (a very difficult procedure to achieve)
- Freezing. Process by which a substance changes from a liquid to a solid by decreasing its temperature. Liquid freezes when its temperature drops below its freezing point (the temperature at which the liquid turns into a solid). For instance: the water that turns into ice cubes.
The difference between the states of aggregation of matter is given by the closeness or distance that exists between the particles that make up that substance. Due to this closeness, the cohesion forces (attractive forces) between the particles will be greater or lesser and that, among other factors, will determine the state of aggregation of a certain substance.
In a liquid state (intermediate cohesion), matter has a defined volume but not a fixed shape; solid matter (with higher cohesion) has a defined shape and the particles are together; matter in the gaseous state (less cohesion) expands freely and does not have a defined volume or shape.
Examples of transition from liquids to solids (solidification and freezing)
- Fruits => ice cream
- Water => ice
- Milk => frozen milk
- Honey => crystallized honey
- Alcohol => solidified alcohol
- Mercury => solidified mercury
- Lava => volcanic stone
Examples of transition from solids to liquids (melting)
- Ice => water
- Sugar => caramel
- Glass => liquid glass
- Chocolate => melted chocolate
- Cheeses => melted cheese
- Butter => melted butter
- Candle => liquid paraffin
- Plastics => liquid plastics
- Metals => molten metals
- Fat => liquid fat / oil