SilberbergChap12ISM

# SilberbergChap12ISM - CHAPTER 12 INTERMOLECULAR FORCES LIQUIDS SOLIDS AND PHASE CHANGES 12.1 The energy of attraction is a potential energy and

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CHAPTER 12 INTERMOLECULAR FORCES: LIQUIDS, SOLIDS, AND PHASE CHANGES 12.1 The energy of attraction is a potential energy and denoted E p . The energy of motion is kinetic energy and denoted E k . The relative strength of E p vs. E k determines the phase of the substance. In the gas phase, E p << E k because the gas particles experience little attraction for one another and the particles are moving very fast. In the solid phase, E p >> E k because the particles are very close together and are only vibrating in place. Two properties that differ between a gas and a solid are the volume and density. The volume of a gas expands to fill the container it is in while the volume of a solid is constant no matter what container holds the solid. Density of a gas is much less than the density of a solid. The density of a gas also varies significantly with temperature and pressure changes. The density of a solid is only slightly altered by changes in temperature and pressure. Compressibility and ability to flow are other properties that differ between gases and solids. 12.2 a) intermolecular b) intermolecular c) intermolecular d) intramolecular 12.3 a) This is because the distance between particles is much greater in the gas. b) This is because the interparticle forces are greater in the solid. 12.4 a) Heat of fusion refers to the change between the solid and the liquid states and heat of vaporization refers to the change between liquid and gas states. In the change from solid to liquid, the kinetic energy of the molecules must increase only enough partially to offset the intermolecular attractions between molecules. In the change from liquid to gas, the kinetic energy of the molecules must increase enough to overcome the intermolecular forces. The energy to overcome the intermolecular forces for the molecules to move freely in the gaseous state is much greater than the amount of energy needed to allow the molecules to move more easily past each other but still stay very close together. b) The net force holding molecules together in the solid state is greater than that in the liquid state. Thus, to change solid molecules to gaseous molecules in sublimation requires more energy than to change liquid molecules to gaseous molecules in vaporization. c) At a given temperature and pressure, the magnitude of Δ Η vap is the same as the magnitude of Δ cond . The only difference is in the sign: Δ vap = – Δ cond . 12.5 a) Condensation The water vapor in the air condenses to liquid when the temperature drops during the n i g h t . b) Fusion (melting) Solid ice melts to liquid water. c) Evaporation Liquid water on clothes evaporates to water vapor. 12.6 a) deposition b) sublimation c) crystallization (freezing) 12.7 The propane gas molecules slow down as the gas is compressed. Therefore, much of the kinetic energy lost by the propane molecules is released to the surroundings upon liquefaction.

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## This note was uploaded on 04/19/2011 for the course CHM 2046 taught by Professor Veige/martin during the Spring '07 term at University of Florida.

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SilberbergChap12ISM - CHAPTER 12 INTERMOLECULAR FORCES LIQUIDS SOLIDS AND PHASE CHANGES 12.1 The energy of attraction is a potential energy and

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