Enthalpy and entropy key definitions

Enthalpy of formation (DfHº)

Enthalpy change when one mole of a substance is formed from its constituent elements with all substances in their standard states.

Exothermic reaction

A reaction that releases energy, resulting in a negative enthalpy change.

Enthalpy of combustion (DcHº)

Enthalpy change when one mole of a substance undergoes complete combustion in oxygen with all substances in standard states.

Enthalpy of neutralisation (DneutHº)

Enthalpy change when 1 mole of water is formed in a reaction between an acid and alkali under standard conditions.

Ionisation enthalpy (DieHº)

The enthalpy change when each atom in one mole of gaseous atoms loses one electron to form one mole of gaseous 1+ ions.

First electron affinity (DeaHº)

Enthalpy change when each atom in one mole of gaseous atoms gains one electron to form one mole of gaseous 1– ions.

Enthalpy of atomisation (DatHº)

Enthalpy change when one mole of gaseous atoms is produced from an element in its standard state.

Hydration enthalpy (DhydHº)

Enthalpy change when one mole of gaseous ions become hydrated (dissolved in water).

Enthalpy of solution (DsolHº)

Enthalpy change when one mole of an ionic solid dissolves in water so that the dissolved ions do not interact with each other.

Bond dissociation enthalpy (DdisHº)

Enthalpy change when one mole of covalent bonds is broken in the gaseous state.

Lattice enthalpy of formation (DLEFHº)

Enthalpy change when one mole of a solid ionic compound is formed from its constituent ions in the gas phase.

Lattice enthalpy of dissociation (DLEDHº)

Enthalpy change when one mole of a solid ionic compound is broken up into its constituent ions in the gas phase.

Enthalpy of vaporisation (DvapHº)

Enthalpy change when one mole of a liquid is turned into a gas.

Enthalpy of fusion (DfusHº)

Enthalpy change when one mole of a solid is turned into a liquid.