Physical and Chemical Equilibria

5.1 Physical Equilibria

Liquid - vapor equilibrium: vapor pressure; relation between vapor pressure and boiling point; liquid mixtures; Raoult's law.

• This sub-section should be taught with the use of models to fractional distillation (as applied to petroleum, liquid air).

Solid - liquid equilibrium: in a pure substance, depression of freezing point.

Solid solute - solvent equilibrium: definition of a saturated solution; fractional crystallization.

Liquid - Liquid equilibrium between two immiscible liquids: (a) Distribution coefficient, D, of a solute between the two liquids. Applications in solvent extraction.

(b) Equilibrium of two immiscible liquids with the vapor steam distillation.

• The distribution law only applies when the solute is in the same molecular state in both solvents. The quantitative effect of association of the solute in one is not required, thought its occurrence should be noted.

Chromatography and ion exchange: Simple consideration using paper and column chromatography.

• Relation to solvent extraction of liquid-liquid chromatography should be brought out. Uses of chromatography and ion exchange in separating mixtures of organic substances, water purification, etc., should be mentioned.

In this section, phase equlibria are considered with an emphasis on practical application in industry and in the laboratory. Phase diagrams should be approached experimentally and built up from experimental results. The practical use of phase diagrams should be emphasized and encouraged. The phase rule is not required and will not be examined. The determination of heat changes associated with phase changes should be treated.

5.2 Chemical Equilibria

Simple experimental demonstration of reversible reactions. The dynamic nature of chemical equilibrium.

• The nature of equilibrium as a macroscopic property should be emphasized.

The principal factors affecting equilibrium: concentration, pressure, temperature - Le Chatelier's principle (illustrated by experiment).

• The Haber process can be treated here to illustrate the industrial importance of equilibrium.

The equilibrium law: equilibrium constants in terms of partial pressures and concentrations of the equilibrium mixture and the rate at which equilibrium is obtained.