Liquids and Intermolecular Forces

A series of practice flashcards covering states of matter, various intermolecular forces, energy changes in phase transitions, and properties of liquid crystals based on the lecture notes.

Condensed phases

The solid and liquid states of matter where particles are closer together than in the gas state.

Intermolecular forces

Attractions between molecules that are strong enough to control physical properties such as boiling points, melting points, vapor pressures, and viscosities.

Van der Waals forces

A group of intermolecular forces consisting of dipole-dipole interactions, hydrogen bonding, and London dispersion forces.

London dispersion forces

Attractions between an instantaneous dipole and an induced dipole present in all molecules, both polar and nonpolar.

Polarizability

The tendency of an electron cloud to distort, allowing for the formation of a dipole.

Dipole-dipole interactions

Attractions between molecules that have permanent dipoles, occurring when the positive end of one molecule is attracted to the negative end of another.

Hydrogen bonding

Unusually strong dipole-dipole interactions experienced when H is bonded to N, O, or F.

Ion-dipole interactions

A fourth type of force important in solutions of ions, whose strength makes it possible for ionic substances to dissolve in polar solvents.

Viscosity

The resistance of a liquid to flow, which increases with stronger intermolecular forces and decreases with higher temperature.

Surface tension

The result of the net inward force experienced by the molecules on the surface of a liquid.

Heat of fusion

The energy required to change a solid at its melting point to a liquid.

Heat of vaporization

The energy required to change a liquid at its boiling point to a gas.

Heat of sublimation

The energy required to change a solid directly to a gas.

Dynamic equilibrium

A state in which liquid molecules evaporate and vapor molecules condense at the same rate.

Boiling point

The temperature at which the vapor pressure of a liquid equals atmospheric pressure.

Normal boiling point

The temperature at which the vapor pressure of a liquid is $760\,\text{torr}$.

Clausius-Clapeyron equation

The equation quantifying the relationship between vapor pressure and temperature: $\ln P = -\frac{\Delta H_{\text{vap}}}{RT} + C$.

Phase diagrams

Displays of the state of a substance at various pressures and temperatures, showing where equilibria exist between phases.

Triple point

The specific temperature and pressure (T) on a phase diagram at which all three states are in equilibrium.

Critical point

The point (C) on a phase diagram above which the liquid and vapor phases are indistinguishable from each other.

Liquid crystals

An intermediate state between solid and liquid where substances have some traits of both, including a degree of molecular order.

Nematic liquid crystals

Liquid crystals in which molecules are ordered in only one dimension, along the long axis.

Smectic liquid crystals

Liquid crystals in which molecules are ordered in two dimensions, along the long axis and in layers.

Cholesteryl liquid crystals

Nematic-like liquid crystals that are layered at angles to each other and can exhibit color changes with temperature changes.