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chem 211 8 notes

chem 211 8 notes - Phases and phase transitions Vapor...

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Phases and phase transitions Vapor pressure At a fixed temp, as long as some liquid is present, the vapor exerts a characteristic pressure regardless of the amount of liguid water present Liquids w/ high vapor pressures are volatile Vapor forms as molecues leave surface of liquid, molecules on surface are least strongly bound As more vapor forms, more vapor molecules get stuck to liquid Rate of condensation= rate of evaporation Volatility and intermolecular forces ΔG vap is standard free energy of vaporazaion: change in molar (gibbs) free energy when a liquid at 1 bar changes to vapor at bar 0 0 ln [ ] [ ] vap vap b initial H S P RT R HB K B + = - + = Vapor pressure of liquid is expected to be low nd its enthalpy of vaporization high if forces between molecues are strong Variation of vapor pressure w/ temperature Vapor pressure of liquid increases as temperature increases 0 2 1 1 2 1 1 ln vap H P P R T T = - clausius-Clapeyron equation Boiling At boiling point, vaporization occurs throughout the liquid, rapid vaporization Normal boiling point is the temperature when the vapor pressure of the liquid is 1 atm Strong intermolecular forces usually lead to high normal boiling points Freezing and melting Freezing temp is when solid and liquid phases are at a dynamic equilibrium at 1 atm Melting point of solid is same temperature at freezing point Often increase w/ pressure Phase diagrams
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