Unit 4 · Chemical Reactions

Physical change ● (core concept) — A change in a substance's properties but not its composition, such as a phase change or separating a mixture.

Chemical change ● (core concept) — A change in which new substances with different compositions form; evidence includes heat or light being produced, gas forming, a precipitate appearing, or a color change.

Balanced chemical equation ● (core concept) — A chemical equation in which atoms and charge are conserved on both sides.

Molecular equation ● (core concept) — A chemical equation written with complete neutral formulas for all reactants and products.

Complete ionic equation ● (core concept) — A chemical equation showing all strong electrolytes as their dissociated ions.

Net ionic equation ● (core concept) — A chemical equation that includes only the species that actually change, omitting spectator ions that appear unchanged on both sides.

Particulate representations of reactions ● (core concept) — Translating between a symbolic chemical equation and a particle-level diagram, which shows how atoms and ions rearrange during a reaction.

Chemical process ● (core concept) — A process involving bond breaking and bond formation, such as a chemical reaction.

Physical process ● (core concept) — A process in which only intermolecular forces change, not chemical bonds — for example, phase changes or the separation of mixtures.

Salt dissolution: physical or chemical process ● (core concept) — Dissolving a salt in water can be plausibly argued as either a physical or a chemical process: ionic bonds are broken and ion-dipole interactions form between ions and water.

Stoichiometry ● (core concept) — Using the mole ratios from a balanced chemical equation to calculate how much product forms from given reactants, or how much reactant is needed.

Limiting reactant ● (core concept) — The reactant that is completely consumed first in a reaction and therefore determines the maximum amount of product that can form.

Titration ● (core concept) — A technique for determining the amount of an analyte by reacting it with a titrant of known concentration.

Analyte ● (core concept) — The substance whose amount is being measured in a titration.

Titrant ● (core concept) — The solution of known concentration added during a titration.

Equivalence point (titration) ● (core concept) — The point in a titration at which the analyte has been completely consumed by the titrant.

Endpoint ● (core concept) — The observable color change of an indicator in a titration, signaling that the equivalence point has been reached.

Acid-base reaction ● (core concept) — A reaction involving the transfer of a proton (H⁺) from an acid to a base.

Oxidation-reduction (redox) reaction ● (core concept) — A reaction involving the transfer of electrons, in which the oxidation numbers of some species change.

Oxidation ● (core concept) — Loss of electrons by a species.

Reduction ● (core concept) — Gain of electrons by a species.

Oxidation number ● (core concept) — A bookkeeping number assigned to each atom, used to identify which species is oxidized and which is reduced in a redox reaction.

Precipitation reaction ● (core concept) — A reaction in which mixing solutions of ions forms an insoluble ionic compound. Salts of Na⁺, K⁺, NH₄⁺, and NO₃⁻ are always soluble.

Combustion reaction ● (core concept) — A subclass of redox reactions in which a species reacts with oxygen; hydrocarbons burn completely to form CO₂ and H₂O.

Brønsted-Lowry acid ● (core concept) — A proton (H⁺) donor.

Brønsted-Lowry base ● (core concept) — A proton (H⁺) acceptor.

Conjugate acid-base pair ● (core concept) — An acid and a base that differ by one proton, formed when a Brønsted-Lowry acid donates its proton to a base.

Water in acid-base reactions ● (core concept) — In aqueous solutions, water can both accept protons from and donate protons to dissolved species, playing an active role in many acid-base reactions.

Half-reaction ● (core concept) — The oxidation half or the reduction half of a redox reaction, written separately; a balanced redox equation is built by combining half-reactions.