What Causes Matter to Change States?

When matter changes states, it's due to the addition or removal of thermal energy. This process is known as a change of state. For example, when a solid turns into a liquid (melting) or a liquid turns into a gas (evaporation), heat energy is added. On the other hand, when a gas turns into a liquid (condensation) or a liquid turns into a solid (freezing), heat energy is removed. These changes occur at specific temperatures known as the melting point, boiling point, and freezing point, which vary depending on the substance.