Final answer:
Changing a solid to a liquid and then to a gas involves phase changes in matter, which occur when heat is added or removed, usually at the substance's melting or boiling point.
Step-by-step explanation:
Changing a solid to a liquid to a gas is changing the phase of matter. These transformations are known as phase changes, which occur when a substance transitions between different states of matter. During a phase change, the addition or removal of heat can cause matter to change phases, typically happening at specific temperatures known as the melting point or the boiling point. The process of changing from a solid to a liquid is called melting, and the transition from a liquid to a gas is referred to as vaporization, which includes boiling and evaporation. Conversely, cooling a substance can cause a gas to become a liquid or a solid, depending on how much heat is removed.