1.8 Thermodynamics definitions

AQA A Level Chemistry

Enthalpy of formation

the enthalpy change when one mole of a substance is formed from its elements with all reactants and products in their standard state. Endo- or exothermic

Enthalpy of combustion

The enthalpy change when one mole of a substance in its standard state is completely burned in oxygen. Exothermic.

Enthalpy of atomisation (element)

The enthalpy change when one mole of gaseous atoms is formed from the element in its standard state. Endothermic.

Enthalpy of atomisation (compound)

The enthalpy change when one mole of a compound in its standard state is converted into gaseous atoms. Endothermic.

Bond dissociation enthalpy

The enthalpy change when one mole of gaseous molecules each breaks a particular covalent bond to form two free radicals. Endothermic.

1st Ionisation enthalpy

The enthalpy change when one mole of gaseous atoms is converted into one more of gaseous, singly charged positive ions. Endothermic

2nd Ionisation enthalpy

The enthalpy change when one mole of gaseous, singly charged positive ions is converted into one mole of gaseous, doubly charged ions. Endothermic

1st electron affinity

The enthalpy change when one mole of gaseous atoms is converted into one mole of gaseous, singly negative ions. Exothermic.

2nd electron affinity

The enthalpy change when one mole of gaseous, singly negative ions is converted into one mole of gaseous, doubly negative ions. Exothermic.

Lattice dissociation enthalpy

The enthalpy change when one mole of an ionic compound is separated into its gaseous ions. Endothermic

Lattice formation enthalpy

The enthalpy change when one mole of an ionic compound is formed from its gaseous ions. Exothermic

Enthalpy of hydration

The enthalpy change when one mole of gaseous ions is converted into one mole of aqueous ions. Exothermic

Enthalpy of solution

The enthalpy change when one mole of an ionic compound completely dissolves in water to give a solution of infinite dilution. Endo-or exothermic