2. Vapor Pressure

3. Evaporation H 2 O(g) molecules (water vapor) H 2 O(l) molecules

4. Evaporation H 2 O(g) molecules (water vapor) H 2 O(l) molecules

5. Evaporation H 2 O(g) molecules (water vapor) H 2 O(l) molecules

6. How Vapor Pressure is Measured 1 atm = 760 mm Hg 760 mm + 120 mm = 880 mm Hg Animation by Raymond Chang All rights reserved

7. Manometer Atmospheric Pressure Zumdahl, Zumdahl, DeCoste, World of Chemistry  2002, page 401

8. Manometer A BIG = small + height ________ = small + __________ 760 mm Hg h = 120 mm 760 mm 120 mm Small = 640 mm Hg ? Zumdahl, Zumdahl, DeCoste, World of Chemistry  2002, page 401

9. Manometer B BIG = small + height BIG = ________ + _________ 760 mm 120 mm BIG = 880 mm Hg 760 mm Hg h = 120 mm ? Zumdahl, Zumdahl, DeCoste, World of Chemistry  2002, page 401

10. The Manometer and Vapor Pressure

11. Barometer & Manometer atmospheric pressure = 101.3 kPa atmospheric pressure = 100.4 kPa atmospheric pressure = 101.7 kPa confined gas confined gas confined gas 600 mm 200 mm 325 mm 150 mm 100 mm 500 mm 750 mm (a) (b) (c) (d)

12. Pressure and Temperature STP (Standard Temperature and Pressure) standard temperaturestandard pressure 1 atm 101.3 kPa 760 mm Hg 273 K 0oC0oC Equations / Conversion Factors: K = o C + 273 o C = K – 273 1 atm = 101.3 kPa = 760 mm Hg

13. Convert 25 o C to Kelvin. K = o C + 273 How many mm Hg is 231.5 kPa? How many kPa is 1.37 atm? 25 o C + 273 298 K = X kPa = 1.37 atm 101.3 kPa 1 atm = 138.8 kPa X mm Hg = 231.5 kPa 760 mm Hg 101.3 kPa = 1737 mm Hg

14. PaPa CONFINED GAS AIR PRESSURE Hg HEIGHT DIFFERENCE manometer: manometer: measures the pressure of a confined gas higher pressure

15. CONFINED GAS AIR PRESSURE Hg HEIGHT DIFFERENCE manometer: manometer: measures the pressure of a confined gas

16. 101.3 kPa Atmospheric pressure is 96.5 kPa; mercury height difference is 233 mm. Find confined gas pressure, in atm. SMALL + HEIGHT = BIG 0.953 atm + 0.307 atm = X atm X = 1.26 atm 96.5 kPa 1 atm + 233 mm Hg 760 mm Hg 1 atm = X atm 96.5 kPa + 233 mm Hg = X atm 233 mm Hg 96.5 kPa X atm BIG small 1.26 atm

17. Vapor Pressure more “sticky” less likely to vaporize In general: LOW v.p. not very “sticky” more likely to vaporize In general: HIGH v.p.  measure of the tendency for liquid particles to enter gas phase at a given temp.  a measure of “stickiness” of liquid particles to each other NOT all liquids have same v.p. at same temp.

18. 020406080 100 0 20 40 60 80 100 TEMPERATURE ( o C) PRESSURE (kPa) CHLOROFORM ETHANOL WATER Volatile substances evaporate easily (have high v.p.’s). BOILING  when vapor pressure = confining pressure (usually from atmosphere) b.p. = 78 o C b.p. = 100 o C atmospheric pressure is 101.3 kPa

19. Vapor Pressure 93.3 80.0 66.6 53.3 40.0 26.7 13.3 0 102030405060708090100 61.3 o C78.4 o C100 o C chloroform ethyl alcohol water Pressure (KPa) Temperature ( o C) 101.3

20. ETHANOL WATER AIR PRESSURE (~100 kPa) VAPOR PRESSURE (~5 kPa) VAPOR PRESSURE (~10 kPa) BOILING  when vapor pressure = confining pressure (usually from atmosphere) At sea level and 20 o C…

21. ETHANOL WATER NET PRESSURE (~95 kPa) NET PRESSURE (~90 kPa)

22. Water Molecules in Liquid and Steam

23. Microscopic view of a liquid near its surface The high energy molecules escape the surface.

24. Behavior of a liquid in a closed container

25. Water rapidly boiling on a stove

26. Copyright © 2006 Pearson Benjamin Cummings. All rights reserved. Pressure Cooker

27. 120 o C

28. Formation of a bubble is opposed by the pressure of the atmosphere Zumdahl, Zumdahl, DeCoste, World of Chemistry  2002, page 452

29. Vapor Pressure 93.3 80.0 66.6 53.3 40.0 26.7 13.3 0 102030405060708090100 61.3 o C78.4 o C100 o C chloroform ethyl alcohol water Pressure (KPa) Temperature ( o C) 101.3

30. Boiling Point and Pressure

31. Vapor Pressure and Boiling Keys Vapor Pressure and Boiling http://www.unit5.org/chemistry/GasLaws.html

32. Heating / Cooling Curve of Water 140 120 100 80 60 40 20 0 -20 Temperature ( o C) Heat added at a constant rate liquid water water and steam steam ice and water ice Heating Cooling

33. Gas Collected Over Water

34. Measuring the Vapor Pressure of a Liquid Davis, Metcalfe, Williams, Castka, Modern Chemistry, 1999, page 376

35. Gas Mixtures and Dalton’s Law

36. Gases Dissolved in Liquids