1. Phase Changes

2.  A PHASE CHANGE is a reversible physical change that occurs when a substance changes from one state of matter to another  The temperature of a substance does not change temperature during a phase change.

3. Phase Changes

4.  Melting Solid changes to liquid  Freezing Liquid changes to solid melting point = freezing point  Sublimation Solid changes to gas EX: dry ice  Vaporization (boiling) liquid changes to gas at the boiling point  Evaporation liquid changes to gas below the boiling point  Condensation Gas changes to liquid  Deposition Gas changes to solid Ex. frost

5. Phase Changes

6. Energy is absorbed or released during a phase change.  Endothermic – absorbs energy from surroundings (gets cold) Endothermic reactions get cold because energy is needed to form the products, which are higher energy than the reactants.  Exothermic - releases energy to surroundings(gets hot) Exothermic reactions release heat because the products are less energy than the reactants. Heat accounts for this extra energy and can be identified by a rising temperature.

7. Endo or Exo?  Which processes are exothermic?  Which processes are endothermic?

8. endothermic is adding heat or energy (ENdothermic heat is ENtering)  Boiling endothermic  Sublimation endothermic  Melting endothermic  Vaporization Endothermic  Evaporation endothermic exothermic is removing heat or energy (EXothermic heat is EXiting)  Freezing exothermic  Condensation exothermic  Deposition exothermic

9. Heating Curves  Kinetic Energy motion of particles related to temperature changes  Potential Energy space between particles related to phase changes

10. B. Heating Curves Solid - KE  Melting - PE  (no temp change) Liquid - KE  Boiling - PE  (no temp change) Gas - KE 

11. Heating Curves  Heat of Fusion energy required to change from solid to liquid (melting)  One gram of ice absorbs 334 joules (J) of energy as it melts some attractive forces are broken Usually energy is needed to break bonds and energy is released when bonds form.

12. Heating Curves  Heat of Vaporization energy required (absorbed) to change from liquid to gas One gram of water gains 2258 joules of energy when it vaporizes at 100° C all attractive forces are broken EX: steam burns, sweating