Vapor Pressure Emily Humpton , Ben Klein, Julia Kuzel

1. Vapor Pressure Emily Humpton, Ben Klein, Julia Kuzel

2. Vapor Pressure- the constant pressure exerted by a vapor (gaseous state of a typically solid or liquid substance) in equilibrium with its liquid or solid phase

3. Dynamic Equilibrium- when two opposing processes occur at the same rate (ex. Condensation and evaporation). The vapor pressure of a liquid is the pressure exerted by its vapor when the liquid and vapor states are in dynamic equilibrium When this occurs the vapor is said to be saturated

4. Volatility, Vapor Pressure and Temperature Dynamic equilibrium does not occur in an open container, therefore open containers do not have vapor pressure High vapor pressure evaporates more quickly and is volatile (gasoline) Low vapor pressure evaporates more slowly and is not volatile (motor oil) As temperature increases, vapor pressure increases

6. Vapor pressure and boiling point Liquids boil when the external and vapor pressures are equal Temperature of boiling point increases with increasing pressure Normal Boiling Point-boiling point at 1 atm http://hyperphysics.phy-astr.gsu.edu/Hbase/Kinetic/vappre.html

7. The varying boiling points depending on pressure are used in real life for pressure cookers and central cooling systems http://media3.washingtonpost.com/wp-dyn/content/graphic/2007/02/20/GR2007022000797.gif

8. Clausius-Clapeyron Equation

9. Questions • 11.37 Explain how each of the following affects the vapor pressure of a liquid: • A) Volume of liquid • B) Surface area • C) Intermolecular attractive forces • D) Temperature • 11.38 A liquid that has an equilibrium vapor pressure of 130mm Hg at 298 K is placed into a 1-L vessel. What is pressure difference shown on manometer, and what is composition of the gas in the vessel if: • 200 mL of liquid is added and frozen at the bottom, then the gas is evacuated. Liquid melts to 298 K • 200 mL of liquid is added at atmospheric pressure, and after a few minutes the vessels is closed off • A few mL of the liquid is introduced into the vessel at 298 K while it has 1atm pressure of air in it, no air escapes. After some time a few drops liquid remain No Affect No Affect When forces increase vp decreases Vp increases with temp. increase Pressure is 130 mm Hg and gas is all evaporated liquid 760mm Hg gas is from part A Still 890mm Hg some gas added from liquid

10. Questions 11.39 Place the following substances in order of increasing volatility: CH4, CBr4, CH2Cl2, CH3Cl, CHBr3, CH2Br2 11.40 PCl3 and AsCl3 are similar substances, with similar geometries and bonding modes. a) Which of these two substances would you expect to be the more volatile at room temperature? b) Which substance would you expect to have the higher boiling point? c) In which substance would the kinetic energies of the molecules be greater than 40º C, a temperature well below either substance’s boiling point? d) In which substance would you expect the intermolecular forces to be larger? CBr4 < CHBr3 < CH2Br2 < CH2Cl2 < CH3Cl < CH4

11. Questions 11.41 a) Two pans of boiling water are on different burners of a stove. One pan of water is boiling vigorously, while the other is boiling gently. What can be said about the temperature of the water in the two pans? b) A large container of water and a small one are at the same temperature. What can be said about the relative vapor pressures of the water in the two containers? 11.42 Explain the following observations: a) Water evaporates more quickly on a hot, dry day than on a hot, humid day. b) It takes longer to cook hard-boiled eggs at high altitudes than low altitudes. The temperature of the water in the two pans is the same. At the same temperature, the vapor pressures of water in the two containers is the same On a dry day, the external pressure is lower, so the water can more easily evaporate At higher altitudes, there is less pressure, and a low vapor pressure allows water to boil at a lower pressure.

12. Questions 11.43 a) Use the vapor-pressure curve in Figure 11.22 to estimate the boiling point of diethyl ether at 400 torr. b) Use the vapor-pressure table in Appendix B to determine the boiling point of water when the external pressure is 25 torr. 11.44 a) Suppose the pressure inside a pressure cooker reaches 1.2 atm. By using the vapor-pressure table in Appendix B, estimate the temperature at which water will boil in this cooker. b) Use the vapor-pressure curve in Figure 11.22 to estimate the external pressure under which ethyl alcohol will boil at 70º C. Approximately 17º C Approximately 28º C 105º C 500 torr

13. Questions 11.45 Mt. Denali in Alaska is the tallest peak in the United States (20,320 ft). a) If the barometric pressure at the top of the mountain is 340 torr, at what temperature will water boil there? Refer to Appendix B. b) If the temperature at the top is 12º C, would a container of diethyl ether experience a pressure greater than the local atmospheric pressure? 11.46 Reno, Nevada, is about 4500 ft above sea level. a) If the barometric pressure is 680 mm Hg in Reno, at what temperature will water boil? Refer to Appendix B. b) What can you say about the average kinetic energies of the water molecules at the boiling point in Reno as compared with those at the boiling point in Chicago, where the barometric pressure is 752 mm Hg? If you believe the average kinetic energies are different, explain how it is that boiling of water can occur at two different average kinetic energies of the water molecules. 75º C The vapor pressure is approximately 325 torr, which is less than the atmospheric pressure of 340 torr 97º C

14. Works Cited Brown, Theodore E., H. Eugene LeMay, and Bruce Edward Bursten. Chemistry : The Central Science. Upper Saddle River: Prentice Hall, 2002. Nave, Rod. "Vapor Pressure." Hyperphysics. Aug. 2000. Georgia State University. 3 Dec. 2008 <http://hyperphysics.phy- astr.gsu.edu/hbase/kinetic/vappre.html>. "Vapor Pressure." Chem Purdue. 2004. Purdue University. 3 Dec. 2008 <http://www.chem.purdue.edu/gchelp/liquids/vpress.html>.