Chapter 11 - CHEMISTRY The Molecular Science Chapter eleven...

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CHEMISTRY The Molecular Science Chapter eleven Liquids, Solids and Materials
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Liquids At a low enough temperature, when the kinetic energy of molecules becomes less than the intermolecular forces between molecules, a gas will begin to condense. Molecules in the liquid phase are mobile. Difficult to compress – distance between molecules is << than that of a gas. Viscosity – resistance of a fluid to flow. – depends on the strength of IFs and shape of molecule. Increase IF increases viscosity. An increase in temperature, decreases viscosity: – molecules have a greater KE to overcome IFs.
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Surface Tension Surface molecules have no IFs above them get pulled into the interior. Less stable than interior molecules. Molecules are the most stable with fewest molecules at its surface sphere. surface tension – resistance of a liquid to increase its surface area.
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Surface Tensions of Some Liquids Molecules with stronger IFs have larger surface tensions.
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Capillary action liquid rises in a small diameter tube due to the IFs between the liquid and the inner wall material.
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Equilibrium Vapor Pressure In a closed system containing only water: Initially rate of evaporation> condensation. After some time rate of evaporation = rate of condensation. EQUILIBRIUM liquid <=> vapor The pressure of the vapor above the liquid surface at equilibrium = vapor pressure. Volatility = ability of substance to vaporize. Higher VP smaller IFs
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Vapor Pressure Increasing temperature increases the KE of liquid molecules. molecules have a greater tendency to escape the liquid surface. larger number of molecules with sufficient energy to escape. increases the vapor pressure.
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Pressure vs. Temperature 0 200 400 600 800 1000 1200 0 20 40 60 80 100 120 Temperature, C Vapor Pressure, torr Water Vapor pressure increases with temperature.
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Boiling Liquids When VP = P atm , a liquid begins to boil throughout liquid <=> vapor Normal bp: VP = 760 mm Hg Differences in bp due to strength of Ifs. Stronger IFs higher bp. Vapor pressure as a function of temperature
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Relative Humidity The vapor pressure of water in the atmosphere: RH = p H2O / p º H2O p H2O = actual partial pressure of water in the atmosphere. p º H2O = equilibrium partial pressure of water. (Table 10.5 p. 458)
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Phase Changes
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Vaporization and Condensation evaporation condensation
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Phase Changes Evaporation - phase change from liquid to gas. Enthalpy of vaporization (ΔH
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This note was uploaded on 10/03/2010 for the course CHE 131 taught by Professor Kerber during the Summer '08 term at SUNY Stony Brook.

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Chapter 11 - CHEMISTRY The Molecular Science Chapter eleven...

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