AP Chem Unit 4

Physical Change

A change in matter's form or phase without change in chemical composition (e.g., melting, dissolving).

Chemical Change

A transformation producing substances with different compositions; evidenced by color change, gas evolution, precipitate formation, heat/light production.

Balanced Chemical Equation

A representation of a reaction where the number of atoms of each element and total charge are equal on both sides.

Molecular Equation

A chemical equation showing full formulas of all reactants and products.

Complete Ionic Equation

A chemical equation showing all soluble ionic compounds dissociated into individual ions.

Net Ionic Equation

A chemical equation showing only the species that actually participate in the reaction (spectator ions removed).

Spectator Ion

An ion present in solution that does not participate in the reaction; appears on both sides of the complete ionic equation.

Law of Conservation of Mass

Matter is neither created nor destroyed in a chemical reaction; total mass of reactants equals total mass of products.

Stoichiometry

The quantitative relationship between reactants and products in a balanced chemical equation; coefficients represent mole ratios.

Limiting Reactant (Reagent)

The reactant that is completely consumed first and determines the maximum amount of product formed.

Excess Reactant

The reactant that remains after the limiting reactant is consumed.

Theoretical Yield

The maximum amount of product calculated from stoichiometry assuming complete reaction.

Percent Yield

(Actual yield / Theoretical yield) × 100%; a measure of reaction efficiency.

Titration

A procedure where a solution of known concentration (titrant) is added to an analyte solution until the reaction is complete; used to determine concentration.

Equivalence Point

The point in a titration where the analyte has been completely consumed by the titrant; stoichiometric amounts have reacted.

Endpoint

The observable event (e.g., color change) that signals the equivalence point in a titration.

Analyte

The substance being measured or identified in a titration or analysis.

Titrant

The solution of known concentration added from a buret during a titration.

Acid-Base Reaction

A reaction involving the transfer of one or more protons (H⁺ ions) between chemical species.

Brønsted-Lowry Acid

A proton (H⁺) donor.

Brønsted-Lowry Base

A proton (H⁺) acceptor.

Conjugate Acid-Base Pair

A pair of species that differ by one proton; HA and A⁻ are a conjugate pair.

Precipitation Reaction

A reaction in which two soluble ionic compounds react to form an insoluble ionic compound (precipitate).

Solubility Rules (AP level)

All sodium, potassium, ammonium, and nitrate salts are soluble in water.

Oxidation-Reduction (Redox) Reaction

A reaction involving the transfer of electrons between species; one species is oxidized, another is reduced.

Oxidation

The loss of electrons; oxidation number increases.

Reduction

The gain of electrons; oxidation number decreases.

Oxidation Number

A number assigned to an atom in a molecule or ion that represents the hypothetical charge it would have if the compound were fully ionic; used to identify redox reactions.

Half-Reaction

A representation of either the oxidation or the reduction portion of a redox reaction; used to balance redox equations.

Combustion Reaction

A redox reaction in which a substance reacts with oxygen gas; complete combustion of hydrocarbons produces CO₂ and H₂O.