1. Phase Changes Any time the state of matter changes, intermolecular forces are “created or destroyed” This requires energy (think temperature or pressure).

2. Phase Changes Evaporation vs. Boiling Evaporation vs. Boiling Evaporation occurs when particles at the surface of a liquid become a gas. Evaporation occurs when particles at the surface of a liquid become a gas. [http://wps.prenhall.com/wps/media/objects/476/488316/Instructor_Resources/Chapter_12/FG12_11.JPG]

3. Phase Changes Boiling occurs when particles throughout the liquid become a gas [http://whatscookingamerica.net/Foto4/BoilingWater.bmp]

4. [http://wps.prenhall.com/wps/media/objects/602/616516/Media_Assets/Chapter10/Text_Images/FG10_12.JPG] Boiling causes liquid to gas conversion to occur faster.

5. Heating Curve Graph that shows temperature of a substance over time. Graph that shows temperature of a substance over time. “Plateaus” represent two phases present. “Plateaus” represent two phases present. Click here for an animation [http://dbhs.wvusd.k12.ca.us/webdocs/NChO/NChO-92-Local-30.GIF]

6. [http://www.bbc.co.uk/schools/ks3bitesize/science/images/sci_dia_21.gif] or condensing or freezing Heating Curve For H 2 O

7. Phase Changes & Thermo q = (m)(s)(ΔT) But ΔT = 0 during a phase change Heat (q) is still being added so a different equation is needed….

8. Phase Changes & Thermo q = (moles of substance)( Δ H phase change ) q = (moles of substance)( Δ H phase change ) How much energy does it take to change 54.0 g of ice to liquid water? How much energy does it take to change 54.0 g of ice to liquid water?

9. Phase Changes & Thermo 54.0 g H 2 O 18.0 g H 2 O 1 mol H 2 O = 3.00 mol H 2 O First, find the moles of water:

10. Phase Changes & Thermo Then, plug into the equation to solve: Then, plug into the equation to solve: q = (3.00 moles)(6.01 kJ/mol) q = (3.00 moles)(6.01 kJ/mol) q = 18.0 kJ of energy q = 18.0 kJ of energy

11. Phase Changes & Thermo What if the temperature changes and the phase changes? What if the temperature changes and the phase changes? Example: Example: How much energy does it take to melt 108 g of ice an heat it to a temperature of 50.0 o C? How much energy does it take to melt 108 g of ice an heat it to a temperature of 50.0 o C?

12. Phase Changes & Thermo q = (moles)(ΔH fus ) + (m)(s)(ΔT) Find the moles of water… 108 g H 2 O 18.0 g H 2 O 1 mol H 2 O = 6.00 mol H 2 O

13. Phase Changes & Thermo

14. q = 36.1 kJ + 22600 J q = 36.1 kJ + 22600 J Or… Or… q = 58.7 kJ q = 58.7 kJ

15. Phase Diagrams Graph that shows how pressure and temperature affect the phases of matter. Graph that shows how pressure and temperature affect the phases of matter. [http://cwx.prenhall.com/bookbind/pubbooks/hillchem3/medialib/me dia_portfolio/text_images/CH11/FG11_10.JPG]

16. [http://library.thinkquest.org/C006669/media/Chem/img/Graphs/Phase.gif]

17. [http://cwx.prenhall.com/bookbind/pubbooks/hillchem3/medialib/media_portfolio/text_images/CH11/FG11_06.JPG]

18. Phase Diagrams The triple point is where all three phases of matter coexist. The triple point is where all three phases of matter coexist. Click here for a video example [http://tbn0.google.com/images?q=tbn:tA2QLC4fXbJWjM:http://img.sc oop.co.nz/stories/images/0611/0c994da3e92a18f9a4cb.jpeg]

19. Dry IceCO 2 Gas