chem chp summaries - Chapter 11 Solids, Liquids, and...

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Chapter 11Solids, Liquids, and Intermolecular Forces (11.1, 11.2, 11.3)The forces that hold molecules or atoms together in a liquid or solid are called intermolecularforces. The strength of the intermolecular forces in a substance determines its phase. Dispersionforces are always present because they result from the fluctuations in electron distribution withinatoms and molecules. These are the weakest intermolecular forces, but they are significant inmolecules with high molar masses. Dipole-dipole forces, generally stronger than dispersionforces, are present in all polar molecules. Hydrogen bonding occurs in polar molecules thatcontain hydrogen atoms bonded directly to fluorine, oxygen, or nitrogen. These are the strongestintermolecular forces. Ion-dipole forces occur in ionic compounds mixed with polar compounds,and they are especially important in aqueous solutions.Surface Tension, Viscosity, and Capillary Action (11.4)Surface tension results from the tendency of liquids to minimize their surface area in order tomaximize the interactions between their constituent particles, thus lowering their potentialenergy. Surface tension causes water droplets to form spheres and allows insects and paper clipsto "float" on the surface of water. Viscosity is the resistance of a liquid to flow. Viscosityincreases with increasing strength of intermolecular forces and decreases with increasingtemperature. Capillary action is the ability of a liquid to flow against gravity up a narrow tube. Itis the result of adhesive forces, the attraction between the molecules and the surface of the tube,and cohesive forces, the attraction between the molecules in the liquid.Vaporization and Vapor Pressure (11.5, 11.7)Vaporization, the phase transition from liquid to gas, occurs when thermal energy overcomes theintermolecular forces present in a liquid. The opposite process is condensation. Vaporization isendothermic and condensation is exothermic. The rate of vaporization increases with increasingtemperature, increasing surface area, and decreasing strength of intermolecular forces. The heatof vaporizationis the heat required to vaporize one mole of a liquid. In a sealed

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Term
Spring
Professor
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