1. The States of matter

2. Phase Rule

3. The phase rule is a useful device for relating the effect of the least number of independent variables (e.g., temperature, pressure, and concentration) upon the various phases (solid, liquid, and gaseous) that can exist in an equilibrium system containing a number of components.

4. Phase rule is expressed as follows:
F= C – P + 2
Where
F is number of degrees of freedom in system,
C is number of components, and
P is number of phases present.

5. The number of degrees of freedom is the least number of intensive variables (temperature, pressure, concentration, refractive index, density, viscosity, etc.) that must be fixed to describe the system completely and here lies the utility of the phase rule.

7. Systems Containing One Component

9. Escaping Tendency
This concept say that the heat in the hotter body has a greater escaping tendency than that in the colder one. Temperature is a quantitative measure of the escaping tendency of heat, and at thermal equilibrium, when both bodies finally have the same temperature, the escaping tendency of each constituent is the same in all parts of the system.

10. A quantitative measure of the escaping tendencies of material substances undergoing physical and chemical transformations is free energy. For a pure substance, the free energy per mole, or the molar free energy, provides a measure of escaping tendency; for the constituent of a solution, it is the partial molar free energy or chemical potential that is used as an expression of escaping tendency.

11. The free energy of 1 mole of ice is greater than that of liquid water at 1 atm above 0°C and is spontaneously converted into water because
∆G = G liq – G ice < 0
At 0°C, at which temperature the system is in equilibrium, the molar free energies of ice and water are identical and ΔG = 0. In terms of escaping tendencies, the escaping tendency of ice is greater than the escaping tendency of liquid water above 0°C, whereas at equilibrium, the escaping tendencies of water in both phases are identical.

12. Thank you for listening