1. Phase Changes Courtesy www.lab-initio.com

2. CA Standards Students know energy is released when a material condenses or freezes and is absorbed when a material evaporates or melts.

3. Water phase changes Temperature remains __________ during a phase change. constant

4. Kinetic Energy, Potential Energy and a Heating Curve. Since Temperature is a measure of "Average Kinetic Energy", any change in temperature is a change in Kinetic Energy. Since temperature does not change during a phase change, the energy that is gained or lost is Potential Energy. Remember the 3 Ps. Plateau, Phase change and Potential Energy Change.

5. Add these abbreviations to graph! PE = Potential energy KE = Kinetic energy KE PE KE PE

6. Exothermic Processes Processes in which energy is released as it proceeds, and surroundings become warmer Reactants  Products + energy

7. Endothermic Processes Processes in which energy is absorbed as it proceeds, and surroundings become colder Reactants + energy  Products

8. Effect of Pressure on Boiling Point

9. Phase Diagram  Represents phases as a function of temperature and pressure.  Critical temperature: temperature above which the vapor can not be liquefied.  Critical pressure: pressure required to liquefy AT the critical temperature.  Critical point: critical temperature and pressure (for water, T c = 374°C and 218 atm).

10. Phase changes by Name

11. Standard Temperature Standard Temperature equals:  273 Kelvin (273 K)  0  C

12. Converting Celsius to Kelvin Many problems involving temperature require that the temperature be in KELVINS! Kelvins =  C + 273 °C = Kelvins - 273

13. Melting point Melting - change from solid to liquid Melting point - SPECIFIC temperature when melting occurs. Each pure substance has a SPECIFIC melting point. M.P. of Water = 0°C (32°F)

14. Boiling Point Boiling Point – temperature at which a liquid boils Each pure substance has a SPECIFIC boiling point. Examples: B.P. of Water = 100°C (212°F)

15. What’s the temperature at point B in kelvins?

16. What’s the temperature at point C in kelvins?

17. Which region is kinetic energy the highest? I II III IV

18. Which region has the lowest potential energy? I II III IV

19. Water

20. Carbon dioxide Phase Diagram for Carbon dioxide

21. Carbon

22. Phase Diagram for Sulfur