Enthalpy Definitions

Enthalpy Change of Reaction (ΔH°)

The standard enthalpy change of reaction is the enthalpy change that accompanies a reaction in the molar quantities shown in a chemical equation under standard conditions with all reactants and products in their standard states.

Enthalpy Change of Formation (ΔH⦵f)

The standard enthalpy change of formation is the enthalpy change that takes place when 1 mole of a compound is formed from its elements under standard conditions, with all reactants and products in their standard states.

Enthalpy Change of Combustion (ΔH°c)

The standard enthalpy change of combustion is the enthalpy change that takes place when 1 mole of a substance reacts completely with oxygen under standard conditions, with all the reactants and products in their standard states.

Enthalpy Change of Neutralisation (ΔHneut)

The standard enthalpy change of neutralisation is the energy change that accompanies the reaction of an acid by a base to form one mole of water under standard conditions, with all reactants and products in their standard states.

Enthalpy of Atomisation (ΔHₐₜ)

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.

First Ionisation Enthalpy (IE₁)

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

Second Ionisation Enthalpy (IE₂)

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

First Electron Affinity (EA₁)

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

The first electron affinity is exothermic for atoms that normally form negative ions. This is due to the fact that the ion is more stable than the atom and there is an attraction between the nucleus and the electron.

Which atoms have an exothermic 1st electron affinity?

Fluorine (F)

Chlorine (Cl)

Bromine (Br)

Iodine (I)

Oxygen (O)

Sulfur (S)

Phosphorus (P)

Second Electron Affinity (EA₂)

The enthalpy change when 1 electron is added to each 1- ion in 1 mole of gaseous 1- ions to produce 1 mole of gaseous 2- ions.

The second electron affinity for oxygen is endothermic because it takes energy to overcome the repulsive force between the negative ion and the electron.

Standard Lattice Enthalpy Of Formation (ΔLEH⦵)

The enthalpy change when one mole of an ionic lattice is formed from its gaseous ions under standard conditions.

Enthalpy of Solution

The enthalpy change that takes place when 1 mole of solute dissolves in water.

Enthalpy of Hydration

Enthalpy change that accompanies the dissolving of gaseous ions to form 1 mole of aqueous ions.

Lattice Enthalpy

The energy released by the formation of 1 mol of Ionic lattices from gaseous ions.