The existence of S,L,G phases is determined uniquely by any two state variables, if only one component is present. Any form of phase transition (L-G, S-L, S-G) can be described by the Clapeyron equation dp/dT=Dh/(T.Dv), where Dh is the latent heat and Dv is the corresponding change of specific volume. From the Clapeyron equation the relationships between pressure and temperature at phase equilibrium can be derived or, on the other hand, knowing the relationship between the equilibrium pressure and temperature p(T), the latent heats can be calculated.
If more than one component is present in the system, a more involved theoretical approach based on chemical potentials ( has to be used (mi - partial derivative of Gibbs energy with respect to the amount of the i-th component, must be the same in both coexisting phases for any component). This general approach can be replaced either by using experimental data in the form of phase diagrams of equilibrium, or by simple laws valid with certain assumptions:
Equilibrium between a mixture of liquids (composition xi) and vapours (pi) can be described by Raoult's law pi=pi"xi if the solution is ideal (mutual interaction of molecules is independent of the nature of the components), and by Dalton's law of additivity of partial pressures p=sum(pi).
Absorption of gases in a liquid phase (e.g., absorption of O2 in water) can be described by Henry's law: pi=Hxi, where H is a proportionality constant (analogous with Raoult's law, the only difference is that Henry's constant H cannot be identified with the equilibrium pressure of saturated vapours pi", because the gas does not exist in the liquid phase at a given temperature). Remark: Please distinguish absorption and adsorption, the former describes absorption of matter, radiation, noise etc., in a volume,
while the latter describes sticking matter to a surface.
We have not discussed the question of miscibility of components. All gases are miscible in any ratio, while only some liquids or solids can form homogeneous solutions. Liquids, to be miscible, should be bound to each other by similar forces. For example, nonpolar hydrocarbons (oils) are immiscible in highly polar water, while polar alcohols form homogeneous water solutions in any ratio (the polarity of alcohols is caused by the polar hydroxyl -OH group).
Solids exist either in a crystalline or in an amorphous form, depending on the composition of molten solids and the rate of cooling during precipitation. All mechanical and thermodynamic properties of solids depend on the arrangement of atoms in a lattice. Compare, e.g., hard and nonconductive diamond with soft and conductive graphite, both materials being pure carbon. When speaking, for example, of ice I, ice II or iron (, iron ( and iron (, we have in mind different crystallographic structures. In the case of mixtures it is the composition and the temperature that determine whether the substance will be a homogeneous solution (substitutional or interstitial, depending on the relative size of the atoms) or a heterogeneous mixture. Phase diagrams of solid mixtures help us to predict the melting point and the structure of a material at different temperatures and compositions and thus to estimate the properties needed for optimal processing and application (see, e.g., http://www.prism.gatech.edu/~wr35/phase_di
Verses for fun:
EQUILIBRIUM p, T, mi
Don't dive too deep,
don't quarrel with your boss,
pressure is dangerous,
his mind should be the same,
dress before sleep,
exactly as yours.
temperature could be less,
And small advice at end:
Never remorse.
mi=dG/dn
Deviated guys with respect to none
have little sense for this stupid fun.
PAPASAX isn't my daddy's saxophone or sax
pA is pA SAt times X.
peoples
mailto: Zitny