What happen when substances change state?

...The motion of the particles change.
The particles of a substance, even a solid, are always in motion. As a solid is heated, its particles gain energy and if the vibrations are fast enough, the particles break loose. The process in which a solid becomes a liquid is known as melting.

As the temperature of a liquid is lowered, its particles lose energy. Eventually, the particles move slowly enough for the attractions between them to cause the liquid to become a solid. This process is called freezing.








Because water freezes at 0°C. Freezing does not happen only in low temperatures, some substances are frozen at room temperature or above. Example: An aluminum can.

When substances lose or gain energy, one of two things can happen:

1. Its teperature change.
2. Its state can change.

But both do NOT happen at the same time.
If you measure the temperature of boiling water, you will find that the temperature stays at 100°C until all of the liquid has become a gas.