D. Ion – Dipole Forces Occurs when an ionic compound is mixed with a polar compound 12
IV. Vaporization and Vapor Pressure Phase is a homogeneous part of the system in contact with other parts of the system but separated from them by a well – defined boundary. 13
A. Vapor Pressure Equilibrium is reached between liquid and vapor, the net number of molecules exchanging does not change. 14
Molar heat of vaporization ( H vap ) is the energy required to vaporize 1 mole of a liquid at its boiling point. ln P = - H vap RT + C Clausius-Clapeyron Equation Vapor Pressure Versus Temperature B. Vapor Pressure and Temperature 15
Example 16 Glacier National Park in Montana is a great vacation spot. It is about 4100 ft above sea level with an atmospheric pressure of 681 mm Hg. At what temperature does water ( H vap = 40.7 kJ/mol) boil in the park?
C. Boiling Point 17 The boiling point is the temperature at which the (equilibrium) vapor pressure of a liquid is equal to the external pressure. The normal boiling point is the temperature at which a liquid boils when the external pressure is 1 atm.
D. Critical Temperature and Pressure 18 There are temperatures and pressures for gasses and liquids that when reached the molecule exhibit unique properties The critical temperature (T c ) is the temperature above which the gas cannot be made to liquefy, no matter how great the applied pressure. The critical pressure (P c ) is the minimum pressure that must be applied to bring about liquefaction at the critical temperature.
V. Phase Diagrams 19 The melting point of a solid or the freezing point of a liquid is the temperature at which the solid and liquid phases coexist in equilibrium. The sublimation of a solid or the deposition of a gas is the temperature at which the solid and gas phases coexist in equilibrium. The vaporization of a liquid or the condensation of a gas is the temperature at which the solid and gas phases coexist in equilibrium.