1. Changes of State Change of state= conversion or a substance from one physical form to another All changes of state are PHYSICAL changes, no changes in identity!

2. Energy and Changes of State During a change of state, energy changes. Energy= related to the motion of its particles Energy added=particles move faster Energy removed= particles move slower Temperature= measure of speed of its particles or a measure of energy

3. Melting: Solids to Liquids Melting= the change of state from a solid to a liquid Example: ice cube melting Melting point= temperature at which the substance changes from solid to liquid Most substances have a unique melting point

4. Melting: Solids to Liquids For a solid to melt, particles must overcome attractions Energy is absorbed= Melting is endothermic Endothermic= energy absorbed in a change of state, takes in heat

5. Freezing: Liquids to Solids Freezing= the change of state from a liquid to a solid Freezing point= the temperature at which a liquid changes into a solid (opposite is melting)

6. Freezing: Liquids to Solids For a liquid to freeze, atoms must slow down and remove energy. Energy is removed= freezing is exothermic Exothermic- energy is removed in a change of state, heat released

8. Vaporization: Liquids to Gases Vaporization= the change of state from liquid to gas Boiling= vaporization that occurs through out a liquid Boiling point= temperature at which a liquid boils Water boils at 100 degrees Celsius. Evaporation= vaporization that occurs at the surface of a liquid below its boiling point Example: sweating

9. Vaporization: Liquids to Gases

10. Pressure affects boiling point The higher you go from sea level, the less air, and the lower the atmospheric pressure

11. Condensation: Gases to Liquids Condensation= change of state from a gas to a liquid Condensation point= temperature at which the gas becomes a liquid and is the same temperature as the boiling point at a given pressure Condensation is exothermic!

13. Sublimation: Solids directly to gases Sublimation= change of state from a solid directly to a gas Example- dry ice We use sublimation to keep food, medicine, and other materials cold without getting them wet. Sublimation is endothermic and requires energy!

14. Comparing changes of State Remember! The state depends on how fast the atoms move and how strongly they are attracted.

15. Comparing changes of State

16. Temperature change VS. change of state Only when a change of state happens, a temperature change occurs. While a substance changes state, temperature change does not occur.

18. Phase change diagram

19. Questions! 1. Compare endothermic and exothermic changes. 2. Classify each change of state (melting, freezing, vaporization, condensation, and sublimation) as endothermic or exothermic. 3. Describe how the motion and arrangement of particles changes as a substance freezers. 4. How are evaporation and boiling different? How are they similar?