Enthalpy Definitions

The standard molar enthalpy of formation, is the enthalpy change when one mole of a compound is formed from its constituent elements under standard conditions, all reactants and products in their standard states.

The standard enthalpy of atomisation, is the enthalpy change which accompanies the formation of one mole of gaseous atoms from the element in its standard state under standard conditions.

First ionisation energy, is the standard enthalpy change when one mole of gaseous atoms is converted into a mole of gaseous ions each with a single positive charge.

The first elecron affinity, is the standard enthalpy change when a mole of gaseous atoms is converted to a mole of gaseous ions, each with a single negative charge.

The second electron affinity, is the enthalpy change when a mole of electrons is added to a mole of gaseous ions each with a single negative charge to form ions each with two negative charges.

Lattice formation enthalpy, is the standard enthalpy change when one mole of solid ionic compound is formed from its gaseous ions.

Enthalpy of hydration, is the standard enthalpy change when water molecules surround one mole of gaseous ions.

Enthalpy of solution, is the standard enthalpy change when one mole of solute dissolves completely in sufficient solvent to form a solution in which the molecules or ions are far enough apart not to interact with each other.

Mean bond enthalpy, is the enthalpy change when one mole of gaseous molecules breaks a covalent bond to form two free radicals, averaged over a range of compounds.