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Aim: I.O.SWBAT: 1)Define vapor pressure 2)Interpret phase change diagrams 3)Describe critical temperature and pressure 4)Draw a phase change diagram MOTIVATION: What happens ice at -25oC if your add heat to it?
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Do-Now: How does the behavior of a liquid in a closed container differ from that in an open one? Vapor: Gas form of a substance that is a solid or a liquid at room temperature.
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LIQUID GAS Dynamic equilibrium: Vaporization and condensation occur at the same rate.
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As more molecules escape the liquid, the pressure they exert increases. Vapor pressure: partial pressure of the vapor over the liquid measured at equilibrium
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At any temperature, some molecules in a liquid have enough energy to escape. As the temperature rises, the fraction of molecules that have enough energy to escape increases.
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Boiling point: is the temperature at which the vapor pressure of a liquid equals the surroundings pressure.
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Vapor Pressure Curves The normal boiling point is the temperature at which its vapor pressure is 760 torr.
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Volatile liquids: Liquids with a high vapor pressure and weak intermolecular forces. (have low boiling points ) Volatility: The tendency of a substance to evaporate easily.
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PRACTICE: 1)Why does the vapor pressure of a liquid depend on intermolecular forces? 2)Why does it take longer to hard boil an egg at high elevations? 3)How does a pressure cooker cook food faster?
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Do-Now: Complete hand-out.
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Phase diagram: Is a graphic representation of the relationships between the physical state of a substance and its pressure and temperature.
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The AB line is the liquid-vapor interface. Each point along this line is the boiling point of the substance at that pressure.
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Triple point (A): solid, liquid and gas are in nequilibrium. Critical point (B): Beyond this temperature gas cannot be liquefied by increasing pressure.
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The AD line is the interface between liquid and solid. The melting point at each pressure can be found along this line.
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Below A the substance cannot exist in the liquid state. Along the AC line the solid and gas phases are in equilibrium. (the sublimation point at each pressure is along this line)
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Phase Diagram of Water The slope of the solid– liquid line is negative. –As the pressure is increased at a temperature just below the melting point, water goes from a solid to a liquid.
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The high critical point of water is due to the strong van der Waals forces between water molecules.
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Phase Diagram of Carbon Dioxide Carbon dioxide cannot exist in the liquid state at pressures below 5.11 atm. CO 2 sublimes at normal pressures. Isotherm: constant temperature Isobar: constant pressure
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PRACTICE: Complete Hand-Out HW#44
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