1.5 Liquids, Solids, and Advanced Phases

Critical Temperature

The temperature above which a liquid phase can no longer exist, regardless of the pressure applied.

Critical Pressure

The minimum pressure required to liquefy a gas at its critical temperature.

Vapor Pressure

The pressure exerted by vapor molecules above a liquid when evaporation and condensation reach dynamic equilibrium.

Boiling Point

The temperature at which the vapor pressure of a liquid becomes equal to the atmospheric pressure.

Crystalline Solids

Solids with a fixed geometric pattern, a definite melting point, and anisotropic properties.

Amorphous Solids

Solids with randomly arranged molecules, no definite melting point, and isotropic properties (supercooled liquids).

Polymorphism

The ability of a chemical compound to exist in more than one crystalline form (same compound, different structures).

Allotropy

A special case of polymorphism occurring in elemental substances, such as graphite and diamond.

Solvates

Crystal forms where residual solvent molecules are trapped inside the crystalline lattice (pseudopolymorphs).

Hydrates

Solvates in which the trapped residual solvent is water.

Anhydrous Crystals

Crystals with no water of crystallization; they typically exhibit higher aqueous solubility than their hydrate forms.

Mesophase

An intermediate phase between solids and liquids, also known as the liquid crystalline state.

Thermotropic LC

Liquid crystals that transition phases as a direct result of temperature changes (heating of solids).

Lyotropic LC

Liquid crystals that form as a result of the action of certain solvents on solids.

Supercritical Fluid

A substance maintained beyond its critical temperature and pressure, exhibiting properties intermediate between a liquid and a gas.

Phase

A homogeneous, physically distinct, and mechanically separable portion of a system that is uniform throughout.

Gibbs Phase Rule

Equation used to find the degrees of freedom: F = (C - P) + 2.

Eutectic Mixture

A combination of two or more components that melts at a lower temperature than any of its individual constituents.

Eutectic Point

The specific temperature and composition where liquid and solid phases of a mixture coexist in equilibrium.