Thermodynamics key definitions

Standard Conditions

298K

100kPa

Standard enthalpy change of formation

Enthalpy change when 1 mole of a compound is formed from its constituent elements under standard conditions, and all species in their standard states

Standard enthalpy change of combustion

Enthalpy change when 1 mole of a substance is completely burnt in oxygen

Standard enthalpy of atomisation

Enthalpy change which accompanies the formation of 1 mole of gaseous atoms from the element in its standard state under standard conditions

First ionisation energy

Standard enthalpy change when 1 mole of gaseous atoms is converted into a mole of gaseous ions, each with a single positive charge

Mg (g) → Mg+ (g) + e-

Second ionisation energy

Loss of a mole of electrons from a mole of singly positively charged ions

Mg+ (g) → Mg2+ (g) + e-

First electron affinity

Standard enthalpy change when a mole of gaseous atoms is converted into a mole of gaseous ions, each with a single negative charge

O (g) + e- → O- (g)

Second electron affinity

Enthalpy change when a mole of electrons is added to a mole of gaseous ions each with a single negative charge to form ions with a 2- charge

O- (g) + e- → O2- (g)

Lattice enthalpy of formation

Standard enthalpy change when 1 mole of solid ionic compound is formed from gaseous ions.

Na+ (g) + Cl- (g) → NaCl (s)

Lattice enthalpy of dissociation

Standard enthalpy change when 1 mole of a solid ionic compound dissociates into its gaseous ions

Enthalpy of hydration

Standard enthalpy change when water molecules surround 1 mole of gaseous ions.

Na+ (g) + aq → Na+ (aq)

Enthalpy of solution

Standard enthalpy change when 1 mole of solution dissolves completely in sufficient solvent to form a solution in which the molecules or ions are far enough apart not to interact with eachother

Mean bond enthalpy

Enthalpy change when 1 mole of gaseous molecules, each breaks a covalent bond to form 2 free radicals, averaged over a range of compounds

Enthalpy change

Heat change at constant pressure