Gen Chem Key Terms Ch.11 & Ch.13 & Ch.16 (up to Rate Law)

antibonding MO

• placing electrons in these orbitals decreases the stability of the molecule

bonding MO

Electrons occupying such an orbital stabilize the molecule.

molecular orbital (MO)

An orbital of given energy and shape that extends over a molecule and can be occupied by no more than two paired electrons.

molecular orbital (MO) diagram

A depiction of the relative energy and number of electrons in each MO, as well as the atomic orbitals from which the MOs form.

molecular orbital (MO) theory

• way to describe bonding between atoms as a combination of their orbitals

• helps predict bond order and bond length which VB theory cannot

pi (π) bond

A covalent bond formed by sideways overlap of two atomic orbitals that has two regions of electron density, one above and one below the internuclear axis.

sigma (σ) bond

A type of covalent bond that arises through end-to-end orbital overlap and has most of its electron density along an imaginary line joining the nuclei.

boiling point elevation (ΔTb)

The increase in the boiling point of a solvent caused by the presence of dissolved solute.

charge density

The ratio of the charge of an ion to its volume.

colligative property

A property of a solution that depends on the number, not the identity, of solute particles. (See also boiling point elevation, freezing point depression, osmotic pressure, and vapor pressure lowering.)

colloid

A heterogeneous mixture in which a dispersed (solute-like) substance is distributed throughout a dispersive (solvent-like) substance.

desalination

A process used to remove large amounts of ions from seawater, usually by reverse osmosis.

dipole-induced dipole force

The intermolecular attraction between a polar molecule and the oppositely charged pole it induces in a nearby molecule.

entropy (S)

A thermodynamic quantity related to the number of ways the energy of a system can be dispersed through the motions of its particles.

fractional distillation

A physical process involving numerous vaporization-condensation steps used to separate two or more volatile components.

freezing point depression (ΔTf)

The lowering of the freezing point of a solvent caused by the presence of dissolved solute particles.

heat of hydration (ΔHhydr)

(also enthalpy of hydration) The enthalpy change occurring when 1 mol of a gaseous species (often an ion) is hydrated. The sum of the enthalpies from separating water molecules and mixing the gaseous species with them; designated ΔHhydr at the standard state.

heat of solution (ΔHsoln)

(also enthalpy of solution) The enthalpy change occurring when a solution forms from solute and solvent. The sum of the enthalpies from separating solute and solvent substances and mixing them; designated ΔHsoln at the standard state.

Henry’s law

A law stating that the solubility of a gas in a liquid is directly proportional to the partial pressure of the gas above the liquid: Sgas = kH × Pgas.

hydration

Solvation in water.

hydration shell

The oriented cluster of water molecules that surrounds an ion in aqueous solution.

ideal solution

A solution that follows Raoult's law at any concentration.

immiscible

Insoluble; usually applied to liquids that do not dissolve in each other.

like-dissolves-like rule

An empirical observation stating that substances having similar kinds of intermolecular forces dissolve in each other.

mass percent [% (w/w)]

(also mass % or percent by mass) The fraction by mass expressed as a percentage. A concentration term expressed as the mass of solute dissolved in 100. parts by mass of solution.

miscible

Soluble in any proportion.

molality (m)

A concentration term expressed as number of moles of solute dissolved in 1000 g (1 kg) of solvent.

mole fraction (X)

A concentration term expressed as the ratio of number of moles of solute to the total number of moles (solute plus solvent).

nonelectrolyte

A substance whose aqueous solution does not conduct an electric current.

osmosis

The process by which solvent flows through a semipermeable membrane from a dilute to a concentrated solution.

osmotic pressure (π)

The pressure that results from the ability of solvent, but not solute, particles to cross a semipermeable membrane. The pressure required to prevent the net movement of solvent across the membrane.

Raoult’s law

A law stating that the vapor pressure of solvent above a solution equals the mole fraction of solvent times the vapor pressure of pure solvent: Psolvent = Xsolvent * P^o solvent.

reverse osmosis

A process for preparing drinkable water that uses an applied pressure greater than the osmotic pressure to remove ions from an aqueous solution, typically seawater.

saturated solution

A solution that contains the maximum amount of dissolved solute at a given temperature (prepared with undissolved solute present).

semipermeable membrane

A membrane that allows solvent, but not solute, to pass through.

solubility (S)

The maximum amount of solute that dissolves in a fixed quantity of a particular solvent at a specified temperature.

solute

The substance that dissolves in the solvent.

solvation

The process of surrounding a solute particle with solvent particles.

solvent

The substance in which one or more solutes dissolve.

strong electrolyte

A substance that is a good conductor of electric current in solution because it dissociates or ionizes completely.

supersaturated solution

An unstable solution in which more solute is dissolved than in a saturated solution.

suspension

A heterogeneous mixture containing particles that are visibly distinct from the surrounding fluid.

Tyndall effect

The scattering of light by a colloid.

unsaturated solution

A solution in which more solute can be dissolved at a given temperature.

vapor pressure lowering (ΔP)

The lowering of the vapor pressure of a solvent caused by the presence of dissolved solute particles.

weak electrolyte

A substance that is a poor conductor of electric current in solution because it only partially dissociates or ionizes.

average rate

The change in concentration of reactants (or products) divided by a finite time period.

initial rate

The instantaneous rate at the moment the reactants are mixed, that is, at t = 0.

collision theory

A model that explains reaction rate as based on the number, energy, and orientation of colliding particles.

instantaneous rate

The reaction rate at a particular time, given by the slope of a tangent to a plot of reactant concentration vs. time.

rate constant (k)

The proportionality constant that relates reaction rate to reactant (and product) concentrations.

rate law

(also rate equation) An equation that expresses the rate of a reaction as a function of reactant (and product) concentrations and temperature.

reaction rate

The change in the concentrations of reactants (or products) with time.