1. Phase Changes Phase Diagrams and Heating Curves

2. Phase Diagrams  Show the phases of a substance at different temps and pressures. Courtesy Christy Johannesson www.nisd.net/communicationsarts/pages/chem

3. Triple Point Plot LeMay Jr, Beall, Robblee, Brower, Chemistry Connections to Our Changing World, 1996, page 488 solid liquid gas melting freezing sublimation deposition vaporization condensation Temperature ( o C) Pressure (atm) 0.6 2.6

4. Liquid VaporSolid Normal melting point Normal boiling point 101.3 0.61 0.016 100 0 Temperature ( o C) Pressure (KPa) Triple point Critical pressure Critical point Critical temperature 373.99 22,058

5. Critical Point  Critical point: the temperature (called critical temperature) above which a substance will always be as gas regardless of the pressure

6. Triple Point  Pressure and temperature where all three phases of matter exist AT THE SAME TIME!!  http://www.youtube.com/watch?v=B LRqpJN9zeA http://www.youtube.com/watch?v=B LRqpJN9zeA

7. Law of Conservation of Energy E after = E before 2 H 2 + O 2  2 H 2 O + energy  Energy Changes +  + WOOF!

8. Law of Conservation of Energy ENERGY CO 2 + H 2 OC 2 H 2 + O 2 PE reactants PE products KE stopper heat, light, sound E after = E before 2 H 2 + O 2  2 H 2 O + energy  Energy Changes +  + WOOF!

9. Law of Conservation of Energy ENERGY C 2 H 2 + O 2 PE reactants PE products KE stopper heat, light, sound E after = E before  Energy Changes 2C 2 H 2 + 5O 2  4 CO 2 + 2H 2 O + energy

10. Heating Curves Temperature ( o C) 40 20 0 -20 -40 -60 -80 -100 120 100 80 60 140 Time Melting - PE  Solid - KE  Liquid - KE  Boiling - PE  Gas - KE 

11. Heating Curves  Temperature Change change in KE (molecular motion) depends on heat capacity  Heat Capacity energy required to raise the temp of 1 gram of a substance by 1°C Water has a very high heat capacity Courtesy Christy Johannesson www.nisd.net/communicationsarts/pages/chem

12. Heating Curves  Phase Change change in PE (molecular arrangement) temp remains constant  Heat of Fusion (  H fus ) energy required to melt 1 gram of a substance at its m.p. Courtesy Christy Johannesson www.nisd.net/communicationsarts/pages/chem

13. Heating Curves  Heat of Vaporization (  H vap ) energy required to boil 1 gram of a substance at its b.p. usually larger than  H fus …why?  EX: sweating, steam burns, the drinking bird Courtesy Christy Johannesson www.nisd.net/communicationsarts/pages/chem