chapter_11revB

chapter_11revB - Vapor Pressure At any temperature, some...

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Unformatted text preview: Vapor Pressure 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. Vapor Pressure: As more molecules escape the liquid, the pressure they exert increases. The liquid and vapor reach a state of dynamic equilibrium: liquid molecules evaporate and vapor molecules condense at the same rate. Vapor Pressure The boiling point of a liquid is the temperature at which its vapor pressure equals atmospheric pressure. The normal boiling point is the temperature at which its vapor pressure is 760 torr. Phase Diagram of H2O The high critical temperature and critical pressure are due to the strong van der Waals forces between water molecules. Phase Diagram for H2O Note the high critical temperature and critical pressure: These are due to the strong van der Waals forces between water molecules. The slope of the solidliquid line is negative.This means that as the pressure is increased at a temperature just below the melting point, water goes from a solid to a liquid. Almost all other crystals have a positive melting slope ! Phase Diagram of Carbon Dioxide Carbon dioxide cannot exist in the liquid state at pressures below 5.11 atm; CO2 sublimes at normal pressures. The low critical temperature and critical pressure for CO2 make supercritical CO2 a good solvent for extracting nonpolar substances (such as caffeine). Solids Solids fall into two groups: Crystalline particles are in highly ordered arrangement. Solids Amorphous--no particular order in the arrangement of particles. Attractions in Ionic Crystals In ionic crystals, ions pack themselves so as to maximize the attractions and minimize repulsions between the ions. ...
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