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13.4 Phase Change

13.4 Phase Change. A. Phase change that requires energy. 1. Melting/MP 2. Vaporization/evaporation. 2. Vaporization/evaporation  liquid -------> vapor (gaseous form of liquid or solid at room temp)

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13.4 Phase Change

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  1. 13.4 Phase Change A. Phase change that requires energy

  2. 1. Melting/MP • 2. Vaporization/evaporation

  3. 2. Vaporization/evaporation  liquid -------> vapor (gaseous form of liquid or solid at room temp) • energy is needed to overcome the intermolecular forces

  4. in order to evaporate • particles must move fast enough to overcome attractive forces • and escape surface into vapor state

  5. Evaporation: • a cooling process • because the faster moving particles escape, • so the avg. K.E. decreases.

  6. open system: liquid can all eventually evaporate • --rate of evap. greater than condensation • Closed—can eventually reach equilibrium

  7. 3. Vapor Pressure • pressure of vapor particles above the liquid • due to collisions of particles with each other and walls of container • Depends on # of vapor particles & temp. • higher temp --> higher vapor pressure

  8. 4. Boiling Point: • temperature at which vapor pressure equals the external or atmospheric pressure • Normal boiling point--at 1 atm. pressure • water =100oC

  9. Boiling point changes with atm. Pressure • lower atm. pressure means lower boiling pt. (mountains) • higher atm. pressure means higher boiling pt. (below sea level) • Why use pressure cooker?

  10. 5. Sublimation • Solid --> Vapor • ex: dry ice moth balls air wicks ice in freezer

  11. B. Phase changes that release energy • 1. Condensation—at certain temperature, particles attracted and group together as liquid • 2. Deposition • 3. Freezing

  12. Freezing Point = Melting Point freezing: Liquid --> Solid melting: Solid --> Liquid(happen at same temp.) Melting--endothermic Freezing--exothermic

  13. MP & BP depend on intermolecular forces stronger attractive forces ==> higher MP disp. dipole H bond Lower M.P. <-------> Higher M.P.

  14. C. Heating Curves:temperature vs. time graph to show energy change GAS Both liquid & gas What is happening at the flat line? Why is the Temp no longer changing? LIQUID Both solid & liquid SOLID E is now used not to make molc move faster, but to break apart IMF!

  15. boiling gas condensation & boiling point condensing Heat of fusion liquid Heat of vaporization melting Melting & freezing point solid freezing Heat Energy added 

  16. 1. -10oC (ice) ----> 0oC (ice) • increase temp, increase avg. K.E. • 2. 0oC (ice) ----> OoC (water) • melting: increase P.E. • overcome hydrogen bonds that hold molecules in fixed positions • molar heat of fusion

  17. 3. 0oC (water) ----> 100oC (water) • increase temp. • overcome more H bonds

  18. 4. 100oC(water) --->100oC(steam) • Boiling • molecules move completely apart • overcome all attractions • molar heat of vaporization

  19. 5. 100oC (steam) ---> 110oC (steam) --increase temp.

  20. phase changes SOLID LIQUID GAS

  21. phase changes SOLID freezing deposition melting sublimation vaporization boiling LIQUID GAS condensation

  22. What is the boiling point of this substance? Vapor Pressure of a Gas torr 1,140 760 380 0 30 60 90 temperature

  23. Kinetic Energy increases as temperature increases • Potential Energy increases as when flat lined. (Energy is used to break bonds instead of raise temp.)

  24. Temp D’s as energy added to ice cube to create steam. Where is Kinetic Energy changing? Where is Potential Energy changing? DKE DPE DKE DPE DKE

  25. Is Kinetic Energy higher at 1 or 2? Why? Both have same Kinetic energy because both at same temp.!

  26. Is Potential Energy higher at 1 or 2? Why? 2 has more Potential Energy because it has gained energy used to break bonds!

  27. What is the boiling point of this substance? Vapor Pressure of a Gas torr 1,140 760 380 0 30 60 90 temperature

  28. Kinetic Energy increases as temperature increases • Potential Energy increases as when flat lined. (Energy is used to break bonds instead of raise temp.)

  29. Temp D’s as energy added to ice cube to create steam. Where is Kinetic Energy changing? Where is Potential Energy changing? DKE DPE DKE DPE DKE

  30. Is Kinetic Energy higher at 1 or 2? Why? Both have same Kinetic energy because both at same temp.!

  31. Is Potential Energy higher at 1 or 2? Why? 2 has more Potential Energy because it has gained energy used to break bonds!

  32. Energy and Phase change Lab(Determining melting & freezing point) • Open Science Folder • Click on Logger Pro 3.4 • Open Chemistry with computers • Open Exp.02 Freeze Melt Water • Click on Experiment & select Connect Interface, LabPro: Com1 (Temp should be about 23o C and time axis needs to be changed to 30 minutes!) • Right click on Time (y-axis) • Select Graph Options & Axes Options Tab • Find x-axis info and change right box from 15 to 30 min

  33. Check time in 30 minutes Check temp.

  34. Place temp probe in test tube ¼ filled w/ dH2O • Click Start • Do not click stop till temp. rises back to room temp! • Gently stir distilled water in salt-ice bath w/ stir rod (Peek at water in test tube every once in while to note phase) • Remove test tube from salt-ice bath when temp is -10oC (that is negative 10 degrees Celsius!) • Allow room temp. to add energy to ice until back at room temp. • Copy graph, close program and do not save, log off • Answer postlab questions

  35. Lab Results

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