Thermodynamics

Enthalpy change of formation

• The enthalpy change when one mole of a compound is formed from it’s constituent elements in standard states under standard conditions.

• 2Na (s) + ½ O2 (g) → Na2O (s)

Enthalpy change of combustion

• Enthalpy change when one mole of a substance reacts with an excess of oxygen, in standard states.

• H2 (g) + ½ O2 (g) → H2O (l)

• Exothermic

Enthalpy change of neutralisation

• Enthalpy change when one mole of water is formed between an acid and alkali under standard conditions.

• ½ H2SO4 (aq) + NaOH (aq) → ½ Na2SO4 (aq) + H2O (l)

• Exothermic

First ionisation enthalpy

• Enthalpy change when each atom in a mole of gaseous atoms loses one electron to form one mole of gaseous 1+ ions.

• Mg (g) → Mg+ (g) + e-

• Endothermic

Second ionisation enthalpy

• Enthalpy change when each ion in a mole of gaseous 1+ ions loses an electron, forming a mole of gaseous 2+ ions.

• Mg+ (g)→ Mg2+(g) +e-

• Endothermic

First electron affinity

• When each atom in a mole of gaseous atoms gains one electron to form one mole of gaseous 1- ions.

• O (g) + e- → O- (g)

• Exothermic

Second electron affinity

• When each ion in a mole of gaseous 1- ions gains one electron to form one mole of gaseous 2- ions.

• O- (g) + e- → O2- (g)

• Endothermic

Enthalpy of atomisation

• Enthalpy change when 1 mole of gaseous atoms is formed from an element in standard states.

• Na (s) → Na (g)

• The enthalpy change for a solid metal turning to gaseous atoms can also be called the Enthalpy of sublimation and will numerically be the same as the enthalpy of atomisation.

• Endothermic

Hydration enthalpy

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

• Mg 2+ (g) +aq → Mg2+ (aq)

• Exothermic

Enthalpy of solution

• Enthalpy change when one mole of an ionic solid dissolves in an amount of water large enough that the dissolved ions are well separated and do not interact with each other.

• MgCl2 (s) +aq → Mg 2+ (aq) + 2Cl- (aq)

Lattice enthalpy of formation

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

• Mg2+ (g) + 2Cl- (g) → MgCl2 (s)

• Exothermic

Lattice enthalpy of dissociation

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

• MgCl2 (s) → Mg2+ (g) +2Cl- (g)

• Endothermic

Enthalpy of vaporisation

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

• H2O (l) → H2O (g)

• Endothermic

Enthalpy of fusion

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

• Mg (s) → Mg (l)

• Endothermic