Enthalpy Change Terms

Enthalpy Change of Reaction

The enthalpy change that accompanies a reaction in the molar quantities shown in a chemical equation under standard conditions, and with everything in its standard state.

Enthalpy change of formation

Enthalpy change when one mole of a substance is formed from its constituent elements under standard conditions, with all the reactants and products in their standard states

2 Na (s) + ½ O²(g) → Na²O (s)

Enthalpy change of combustion

Enthalpy change when one mole of a substance reacts completely with oxygen under standard conditions, with all the reactants in their standard states

H² (g) + ½ O² (g) → H²O (l)

Enthalpy change of neutralisation

Energy change that accompanies the reaction of an acid by a base to produce 1 mole of water (l), under standard conditions with all the reactants in their standard states.

Enthalpy change of atomisation

The enthalpy change that takes place for the formation of 1 mole of gaseous atoms from the element in its standard state under standard conditions.

½ Br2(l) → Br(g)

First Ionisation enthalpy

The enthalpy change required to remove one electron from each atom in 1 mole of gaseous atoms to form one mole of gaseous 1+ ions

Second ionisation enthalpy

The enthalpy change required to remove one electron from one mole of gaseous 1+ ions to produce one mole of gaseous 2+ ions.

First Electron affinity

The enthalpy change that occurs when 1 electron is added to each atom in one mole of gaseous atoms to form one mole of gaseous 1- ions

Second electron affinity

The enthalpy change that occurs when 1 electron is added to each atom in one mole of gaseous 1- ions to form one mole of gaseous 2- ions.

Enthalpy change of solution

The enthalpy change that takes place when one mole of solute dissolves in a solvent.

NaCl(s) + aq → Na+(aq) + Cl-(aq)

Enthalpy of Hydration

Enthalpy change that accompanies the dissolving of gaseous ions to form one mole of aqueous ions.

X+/X- + aq → X+/X- (always exothermic)

Average bond enthalpy

The energy required to break one mole of bonds in gaseous molecules

Lattice Enthalpy

Enthalpy change when one mole of ionic lattice is formed from its gaseous ions