Liquids and Solids_S13 - LIQUIDS AND SOLIDS VAPOR PRESSURE...

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LIQUIDS AND SOLIDS VAPOR PRESSURE AND CHANGES OF STATE Vapor Pressure It is the partial pressure exerted on the surface of a substance by its vapor that is in dynamic equilibrium with the condensed phase in a closed container. Ex: H 2 O (l) H 2 O (g) We have dynamic equilibrium when the rate of evaporation of water = the rate of its condensation at a certain temperature. At this point, one can measure the vapor pressure. A liquid in a closed container Zumdahl, S. S. Chemical Principles , 6 th ed.; Boston: Houghton Mifflin Company, 2010. The rates of condensation and evaporation over time for a liquid sealed in a closed container Zumdahl, S. S. Chemical Principles , 6 th ed.; Boston: Houghton Mifflin Company, 2010. 1
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At a fixed temperature, the vapor pressure of a liquid is constant. Liquids with high vapor pressure at room temperature are called volatile . Ex: ethanol, dimethyl ether, acetaldehyde… (What can you say about the intermolecular forces of such liquids?) Solids have much lower vapor pressure than liquids. The process by which solids vaporize is called ………………. Ex: moth balls, dry ice, iodine... Vapor Pressure and Intermolecular Forces As the strengths of intermolecular forces decrease, vaporization …………… As the vaporization increases, the vapor pressure ……………….. Compare the vapor pressure of dimethyl ether and ethanol: dimethyl ether ethanol Compare the vapor pressure of pentane and decane: pentane decane Compare the vapor pressure of acetone and 1-propanol: Acetone 1-propanol 2
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The Variation of Vapor Pressure with Temperature Number of molecules in a liquid with given energy vs. kinetic energy: (a) at a lower temperature T 1 ; (b) At a higher temperature, T 2 Zumdahl, S. S. Chemical Principles , 6 th ed.; Boston: Houghton Mifflin Company, 2010.
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