A change of state occurs when matter is converted from one physical state to another. For example, when water is heated, it changes from a liquid to a gas. A change of state is usually accompanied by a change intemperature and/or pressure.

Matter commonly exists in one of three forms, or states: solid, liquid, or gas. One fundamental way in which these three states differ from each other is the energy of the particles of which they are made. The particles in a solid contain relatively little energy and move slowly. The particles in a liquid contain more energy and move more rapidly. The particles in a gas contain still more energy and move still more rapidly.

The state in which matter occurs can be changed by adding or removing energy. When water is heated, heat energy is added to water molecules...