Chapter 11 CHM 108 Fall 2011 Suroviec
A. Changes between phases • Using temperature, pressure or both you can convert from one phase to another
II. Intermolecular Forces • Originate from interactions between charges, partial charges and temporary charges
II. Intermolecular Forces • Looking at the difference between an O-H bond and 2 H2O molecules
A. Dispersion Forces • One intermolecular force present in all molecules and atoms s the dispersion force
A. Dispersion Forces • Magnitude of dispersion force depends on how easily the atom/molecule can polarize
B. Dipole – Dipole Forces • Exists in all molecules that are polar – that have permanent dipoles.
B. Dipole – Dipole Forces • Polarity is important in determining miscibility
C. H – Bonding • hydrogen bond = a special dipole-dipole interaction between they hydrogen atom in a polar N-H, O-H, or F-H bond and an electronegative O, N, or F atom.
D. Ion – Dipole Forces • Occurs when an ionic compound is mixed with a polar compound
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.
A. Vapor Pressure • Equilibrium is reached between liquid and vapor, the net number of molecules exchanging does not change.
Clausius-Clapeyron Equation ln P = - Vapor Pressure Versus Temperature DHvap + C RT B. Vapor Pressure and Temperature Molar heat of vaporization (DHvap) is the energy required to vaporize 1 mole of a liquid at its boiling point.
Example • 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 (DHvap = 40.7 kJ/mol) boil in the park?
C. Boiling Point • 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 • There are temperatures and pressures for gasses and liquids that when reached the molecule exhibit unique properties • The critical temperature (Tc) is the temperature above which the gas cannot be made to liquefy, no matter how great the applied pressure. • The critical pressure (Pc) is the minimum pressure that must be applied to bring about liquefaction at the critical temperature.
V. Phase Diagrams • 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.