CHM 108Suroviec

Spring 2014

Chapter 111

I. Solids, Liquids and Gasses2

A. Changes between phases

Using temperature, pressure or both you can convert from one phase to another

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II. Intermolecular Forces

Originate from interactions between charges, partial charges and temporary charges

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II. Intermolecular Forces

Looking at the difference between an O-H bond and 2 H2O molecules

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A. Dispersion Forces

One intermolecular force present in all molecules and atoms s the dispersion force

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A. Dispersion Forces

Magnitude of dispersion force depends on how easily the atom/molecule can polarize

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B. Dipole – Dipole Forces

Exists in all molecules that are polar – that have permanent dipoles.

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B. Dipole – Dipole Forces

Polarity is important in determining miscibility

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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.

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D. Ion – Dipole Forces

Occurs when an ionic compound is mixed with a polar compound

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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.

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A. Vapor Pressure

Equilibrium is reached between liquid and vapor, the net number of molecules exchanging does not change.

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Molar heat of vaporization (Hvap) is the energy required to vaporize 1 mole of a liquid at its boiling point.

ln P = -Hvap

RT+ C

Clausius-Clapeyron Equation

Vapor Pressure Versus Temperature

B. Vapor Pressure and Temperature15

Example16

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 (Hvap = 40.7 kJ/mol) boil in the park?

C. Boiling Point17

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

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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 Diagrams19

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.

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