1. Change of State Change of state is the change of a substance from one physical form to another. ALL CHANGES OF STATE ARE PHYSICAL CHANGES

2. Melting (endothermic) heat in Melting is the change of state from a solid to a liquid. Adding energy to a solid increases the temperature. As the temperature increases, the particles of the solid move faster and faster. Once the substance reaches it’s MELTING POINT, it becomes a liquid.

3. Boiling (endothermic) heat in Boiling is the change of a liquid to a vapor or gas. Boiling occurs when the vapor pressure of the substance reaches the atmospheric pressure. The temperature at which this occurs is called the boiling point.

4. Sublimation (endothermic) heat in Sublimation is the change of state where a solid turns directly into a gas. Skipping the liquid phase. During sublimation, the particles must gain enough energy to overcome their attraction, going from being very tightly packed together (as a solid) to rapidly moving and spreading apart (as a gas).

5. Freezing (exothermic) heat leaving Change of state from a liquid to a solid. Freezing is the reverse of melting so the melting point and freezing point for a substance is the same. During the freezing process, energy is removed from the substance causing the particles to slow which creates an attraction between them. The particles slow until they lock (or freeze) into place.

6. Evaporation Evaporation is the change of a substance from a liquid to a gas. Evaporation does not mean boiling. A substance can evaporate without boiling, for example sweat.

7. Condensation (exothermic) heat leaving Condensation is the change of state from a gas to a liquid. The condensation point is the temperature at which a gas becomes a liquid. During condensation, the fast moving particles of a gas clump together as energy (or heat) is removed.

8. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Section 3 Changes of State Chapter K2

9. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Exit Ticket Explain why freezing is an exothermic reaction.