Facts At Your Fingertips: Matter and materials – Changing states
A substance may not always remain in the same state of matter. It can change state when it is at different temperatures.
For example, a solid can become a liquid if it becomes hot enough and a liquid may become a solid if it is cooled enough.
Boiling and evaporation
When water is heated to boiling point, bubbles appear.
These bubbles are made because some of the liquid has changed to an invisible gas called water vapor, or steam. Water boils at 212°F (100°C). The water vapor escapes into the air in a process called evaporation. Evaporation can also occur more slowly. For example, wet hair dries because of evaporation.
Condensation
The opposite of evaporation is condensation and this process occurs when a gas cools and becomes a liquid. When water vapor comes into contact with something cool, it turns back into a liquid. Condensation often forms on windows as the temperature drops overnight.
Freezing
When a liquid becomes cold enough, it will freeze and become a solid. The temperature at which a substance turns into a solid is called its freezing point.
Water freezes at 32ºF (0ºC) and its solid state is called ice. Jet fuel freezes at around −52°F (−47°C).
Melting
When a solid is heated to a high enough temperature, it becomes a liquid, or melts. The increase in temperature causes the particles in the solid to move more freely until eventually they achieve a liquid state.
The temperature at which a solid becomes a liquid is known as its melting point. The melting point and freezing point of a substance are the same temperature.