IB Chemistry Reactivity 3. What Are the Mechanisms of Chemical Change? Key Definitions

The equilibrium constant for the dissociation of a weak acid in water, $K_a = \mathrm{\frac{[H^+][A^-]}{[HA]}}$. A larger value of $K_a$ means the acid dissociates more fully, so it is a stronger acid.

Acid–base indicators are weak acids that exist in equilibrium between their protonated form (HInd) and deprotonated form (Ind⁻).

An amphiprotic species is a chemical species that can either donate a proton (acting as an acid) or accept a proton (acting as a base), depending on the reaction conditions.

The anode is the electrode in an electrochemical cell where oxidation occurs. Electrons are produced at the anode and flow into the external circuit.

The positively charged, non-aromatic intermediate formed when a benzene ring donates a pair of π-electrons to an electrophile. Its delocalized system is broken, so it is less stable than benzene.

A Brønsted–Lowry acid is a proton (H⁺) donor, which gives up a hydrogen ion in a reaction.

A Brønsted–Lowry base is a proton (H⁺) acceptor, which gains a hydrogen ion in a reaction.

The Brønsted–Lowry theory, introduced in 1923, defines acids and bases based on their ability to transfer protons (H⁺ ions).

Buffers are solutions that resist changes in pH when small amounts of acid ($H⁺$ ions) or base ($OH⁻$ ions) are added.

A carbocation is a carbon atom that carries a positive charge, formed when a bond is broken heterolytically, leaving the carbon electron-deficient.

The cathode is the electrode in an electrochemical cell where reduction occurs. Electrons arrive at the cathode from the external circuit.

A conjugate acid–base pair consists of two species that differ by exactly one proton ($H^+$).

A coordination bond (also known as a dative covalent bond) forms when both electrons in the shared pair come from the same atom.

An electrochemical cell is a device that uses redox (reduction-oxidation) reactions to either produce or consume electrical energy.

Electrodes are solid surfaces where the redox reactions occur

Electrolysis uses electrical energy to drive non-spontaneous redox reactions.

An electrolytic cell is a device that uses electrical energy to force a non-spontaneous redox reaction to occur.

An electrophile is a species that accepts an electron pair to form a covalent bond.

Electroplating is a process that uses an electrolytic cell to coat an object (usually the cathode) with a thin layer of metal.

The equilibrium constant $K$ is a ratio that provides a snapshot of the relative concentrations of products and reactants at equilibrium for a reversible chemical reaction.

The equivalence point in a titration is the precise moment when the amount of base added is chemically equivalent to the amount of acid initially present.

Gibbs free energy ($\Delta G$) is a thermodynamic property that determines whether a chemical reaction is spontaneous under constant pressure and temperature.

A half-equation focuses on one part of a redox reaction: either the oxidation or reduction process.

In chemistry, heterolytic fission refers to the breaking of a covalent bond where both bonding electrons are transferred to one of the two bonded atoms.