A-level AQA Chemistry • Thermodynamics Definitions

Standard Enthalpy of Formation (-ve)

Enthalpy change when one mole of a compound is formed from its constituent elements under standard conditions, all reactants and products are in standard states.

Standard Enthalpy change of Combustion (-ve)

Enthalpy change that accompanies the formation of one mole of substance completely burned in oxygen.

Standard Enthalpy of Atomisation (+ve)

Enthalpy change which accompanies the formation of one mole of gaseous atoms from the element in the standard states and standard conditions.

First ionisation energy (+ve)

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

Second ionisation energy (+ve)

Standard enthalpy change when one mole of gaseous single positive charged ions are converted into double charged ions.

First electron affinity (-ve)

Standard enthalpy change when one mole of gaseous atoms gain one electron to form an ion with a single negative charge.

Second electron affinity (+ve)

Standard enthalpy change when one mole of negatively charged ions gain an electron.

Lattice enthalpy of formation (-ve)

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

Enthalpy of solution (+/-ve)

One mole of ionic compound is dissolved in water under standard conditions.

Standard enthalpy of hydration (-ve)

One mole of aqueous ions are formed from their gaseous ions under standard conditions.

Lattice enthalpy of dissociation (+ve)

Standard enthalpy change when one mole of solid ionic compound dissociated into its gaseous ions.

Mean bond enthalpy (-ve)

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