Learn refrigeration

There are three commonly recognized states of matter solid, liquid and gas.

The solid state of matter is when the material has a definite volume or size and distinct shape at a given temperature.  

Solid to Liquid 

If heat energy is added to a solid, its molecules begin to vibrate more rapidly until they break out of their fixed positions and the solid becomes a liquid. The change from solid to liquid is called melting and occurs at a definite temperature, the Melting Point. The molecules of a liquid are free to move throughout the liquid but are held from escaping from the liquid by intermolecular forces. This gives a liquid a definite volume but no definite shape.

Liquid to Vapour

As more heat is added to the liquid, some molecules gain enough energy to break away completely from the liquid and escape into the surrounding space. Finally a temperature is reached at which molecules throughout the liquid are becoming energetic enough to escape and bubbles of vapor form and rise to the surface.

The change of the liquid to a vapor, or gas, in this manner is called boiling and occurs at the boiling Point. The molecules of a gas are free to move in every possible way. A gas has neither a definite shape nor a definite volume but expands to fill any container in which it is placed.