Chemistry A level Definitions (Chp 19 - 30)

Chemistry Definitions:

Standard enthalpy change of atomisation, ΔH_at: Enthalpy change when 1 mole of gaseous atoms is formed from its element under standard conditions.

Standard enthalpy change of hydration, ΔH_hyd: Enthalpy change when 1 mole of a specified gaseous ion dissolves in a sufficient amount of water to form a very dilute solution under standard conditions.

Standard electrode potential: Voltage produced when a standard half-cell (ion concentration 1.00 mol/dm³ at 298 K) is connected to a standard hydrogen electrode under standard conditions.

Standard cell potential: Difference in standard electrode potential between 2 specified half-cells.

Conjugate pair(acid-base): Acid-base pair on each side of an acid-base equilibrium equation that are related to each other by the difference of a hydrogen ion, e.g. the acid in the forward reaction and the base in the backward reaction.

Ionic product of water, K_w: Equilibrium constant for ionisation of water. K_w = [H⁺][OH^-]

Acid dissociation constant, K_a: Equilibrium constant for the dissociation of a weak acid.

Buffer solution: A solution that minimises changes in pH when moderate amounts of acid or base are added.

Solubility product, K_sp: Product of the concentrations of each ion in a saturated solution of a sparingly soluble salt at 298K, raised to the power of their relative concentrations.

Half-time, t_1/2: Time taken for the amount (or concentrations) of the limiting reactant in a reaction to decrease to half its initial value.

Homogeneous Catalysis: A type of catalysis in which the catalyst and reactants are in the same phase.

Heterogeneous Catalysis: A type of catalysis in which the catalyst is in a different phase from the reactants.

Entropy: Number of possible arrangements of the particles and their energy in a given system.

Surrounding (in enthalpy changes): Anything other than the chemical reactants and products.