Explain the Process of Phase Changes

Matter exists in three forms: as a solid, a liquid or as a gas. These are called phases of matter. If we take a chunk of ice (solid water) from the freezer and leave it in a pan on the kitchen counter, it is easy to predict that it will melt (become liquid water). If you then place the pan of water on the stove and heat it, it will boil and evaporate (become gaseous water - water vapor).

Typically, as you add heat to a solid, it expands and becomes a liquid, which expands and becomes a gas. The gas will then continue to expand as it is heated.