Chapter 16 Notes - Chapter 16.10 and 16.11: PHASE CHANGES...

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Chapter 16.10 and 16.11: PHASE CHANGES VAPOR PRESSURE Figure 16.44: Behavior of a liquid in a closed container. Initially mostly evaporation occurs, but eventually rate of evaporation equals rate of condensation At equilibrium: if NO other gas present than liquid’s vapor, P = Vapor Pressure of liquid = P vap VP is INDEPENDENT of container size - as long as there’s SOME liquid! Measuring vapor pressure of a liquid using a simple barometer. Figure 16.46: Ordinarily the height of Hg in the column is a measure of atmospheric pressure But if some liquid is trapped in the top of a second mercury barometer, it generates a VP which then forces some Hg down the tube. The two barometers can be compared to see the VP of the liquid in the second barometer. Why vapor pressure rises steeply with increasing temperature: Figure 16.47: Attractive forces tend to discourage evaporation and encourage condensation. Molecules must break free of the bulk liquid to evaporate! As T increases more of them have enough KE to do so! Figure 16.48: Vapor pressure of water, ethanol, and diethyl ether as a function of temperature. The STRONGER the IM forces . .... the LOWER the vapor pressure of the gas! BOILING: When its VP = Ambient P, a liquid BOILS. Normal boiling point: Temperature when VP =
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Chapter 16 Notes - Chapter 16.10 and 16.11: PHASE CHANGES...

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