Chapter 11 CHEM VOCABULARY

The short-range attractive forces operating between the particles that make up the units of a liquid or solid substance. These same forces also cause gases to liquefy or solidify at low temperatures and high pressures.

Intermolecular Forces

Intermolecular forces resulting from attractions between induced dipoles. Also called London dispersion forces

Dispersion (London) Forces

A force that becomes significant when polar molecules come in close contact with one another. The force is attractive when the positive end of one polar molecule approaches the negative end of another

Dipole- Dipole Forces

Bonding that results from intermolecular attractions between molecules containing hydrogen bonded to an electronegative element. The most important examples involve OH, NH, and HF

Hydrogen Bonding

The ease with which the electron cloud of an atom or a molecule is distorted by an outside influence, thereby inducing a dipole moment.

Polarizability

The force that exists between an ion and a neutral polar molecule that possesses a permanent dipole moment.

ion- dipole force

A measure of the resistance of fluids to flow.

Viscosity

The intermolecular, cohesive attraction that causes a liquid to minimize its surface area.

Surface Tension

The process by which a liquid rises in a tube because of a combination of adhesion to the walls of the tube and cohesion between liquid particles.

Capillary Action

The conversion of a substance from one state of matter to another. The phase changes we consider are melting and freezing 1solid ∆ liquid2, sublimation and deposition, and vaporization and condensation

Phase Changes

The enthalpy change, ∆H, for melting a solid.

Heat of Fusion

A graphic representation of the equilibria among the solid, liquid, and gaseous phases of a substance as a function of temperature and pressure

phase diagram

The enthalpy change, ∆H, for vaporization of a solid

heat of sublimation

The enthalpy change, ∆H, for vaporization of a liquid

heat of vaporization

The highest temperature at which it is possible to convert the gaseous form of a substance to a liquid. The critical temperature increases with an increase in the magnitude of intermolecular forces

Critical Temperature

The pressure at which a gas at its critical temperature is converted to a liquid state.

critical pressure

When the temperature exceeds the critical temperature and the pressure exceeds the critical pressure, the liquid and gas phases are indistinguishable from each other

supercritical fluid

The pressure exerted by a vapor in equilibrium with its liquid or solid phase.

vapor pressure

A state of balance in which opposing processes occur at the same rate

Dynamic Equilibrium

Tending to evaporate readily.

Volatile

The boiling point at 1 atm pressure.

Normal Boiling Point

The melting point at 1 atm pressure.

Normal Melting Point

The temperature at which solid, liquid, and gas phases coexist in equilibrium.

Triple Point

A substance that exhibits one or more partially ordered liquid phases above the melting point of the solid form. By contrast, in nonliquid crystalline substances the liquid phase that forms upon melting is completely unordered.

Liquid Crystal

A liquid crystal in which the molecules are aligned in the same general direction, along their long axes, but in which the ends of the molecules are not aligned.

Nematic Liquid Crystal

A liquid crystal in which the molecules are aligned along their long axes and arranged in sheets, with the ends of the molecules aligned. There are several different kinds of smectic phases.

Smectie Liquid Crystal

A liquid crystal formed from flat, disc-shaped molecules that align through a stacking of the molecular discs.

Cholesteric Liquid Crystal