chem 2

Solubility Rule

"Like dissolves like"—polar solvents dissolve polar/ionic solutes; nonpolar solvents dissolve nonpolar solutes.

Saturated Solution

A solution containing the maximum amount of solute that can be dissolved at a given temperature.

Supersaturated Solution

An unstable solution that contains more dissolved solute than a saturated solution; excess solute will precipitate if disturbed.

Henry's Law Concept

The solubility of a gas in a liquid is directly proportional to the partial pressure of that gas above the liquid.

Raoult's Law Concept

The vapor pressure of a solvent decreases when a non-volatile solute is added because solute particles occupy the surface.

Colligative Property

A property that depends only on the number of solute particles present, not on their identity.

van't Hoff Factor (i)

The ratio of moles of particles in solution to moles of solute dissolved; used for ionizing compounds (electrolytes).

Colloid

A mixture where particles are larger than molecules but small enough to remain suspended; characterized by the Tyndall Effect (scattering light).

Factors Affecting Reaction Rate

Concentration, temperature, surface area, and the presence of a catalyst.

Reaction Order

Defined by the exponents in a rate law; determined only by experimental data, not stoichiometric coefficients.

Zero Order Reaction

A reaction where the rate is independent of the concentration of the reactant.

First Order Reaction

A reaction where the rate is directly proportional to the concentration of one reactant.

Collision Theory

Reactants must collide with sufficient energy (Activation Energy) and correct orientation to react.

Activation Energy (Ea)

The minimum energy required to initiate a chemical reaction.

Catalyst

A substance that increases reaction rate by providing an alternative pathway with a lower activation energy; it is not consumed.

Reaction Intermediate

A species produced in one step of a mechanism and consumed in a subsequent step.

Rate-Determining Step

The slowest step in a multi-step reaction mechanism that limits the overall reaction rate.

Dynamic Equilibrium

The state where the rates of the forward and reverse reactions are equal, and concentrations remain constant.

Equilibrium Constant (K)

The ratio of product concentrations to reactant concentrations at equilibrium, each raised to the power of their coefficients.

Excluded Species in K

Pure solids (s) and pure liquids (l) are never included in equilibrium expressions because their concentrations are constant.

Reaction Quotient (Q)

A value calculated using the same expression as K but with non-equilibrium concentrations to determine the direction of shift.

Q < K

The system will shift to the right (toward products) to reach equilibrium.

Q > K

The system will shift to the left (toward reactants) to reach equilibrium.

Le Chatelier's Principle

If a system at equilibrium is stressed, the position of the equilibrium will shift in the direction that relieves the stress.

Pressure Shift (Gases)

Increasing pressure (by decreasing volume) shifts the equilibrium toward the side with fewer moles of gas.

Temperature Shift (Exothermic)

Increasing temperature shifts the equilibrium toward the reactants (left) as heat is treated as a product.

Temperature Shift (Endothermic)

Increasing temperature shifts the equilibrium toward the products (right) as heat is treated as a reactant.