5.2.1 Lattice Enthalpy

What is lattice enthalpy?

The enthalpy change that accompanies the formation of one mole of an ionic compound from its gaseous ions under standard conditions

What is lattice enthalpy used as a measure of?

Strength of an ionic bond

What is the lattice enthalpy of NaCl (s)?

Na+ (g) + Cl- (g) —> NaCl (s)

Are lattice enthalpies endothermic or exothermic?

Always exothermic

Requires the formation of ionic bonds which is exothermic

What is the standard enthalpy change of formation?

Enthalpy change that occurs when one mole of a compound is formed from its constituent elements under standard conditions with all reactants and products in their standard states

Are standard enthalpy changes of formation in general exothermic or endothermic?

Exothermic

What is the standard enthalpy change of atomisation?

The enthalpy change that takes place when one mole of gaseous atoms form from the element in its standard state

What is the standard enthalpy change of atomisation of Ca?

Ca (s) —> Ca(g)

Are standard enthalpies of atomisation endothermic or exothermic and why?

Always endothermic

Requires energy to overcome the intermolecular forces

What is the first ionisation energy?

Enthalpy change that occurs when one mole of electrons is removed from one mole of gaseous atoms to form one mole of gaseous 1+ ions

Are first ionisation energies endothermic or exothermic?

Endothermic

What is second ionisation energy?

Enthalpy change that occurs when one mole of electrons is removed from one mole of gaseous 1+ ions to form one mole of gaseous 2+ ions

Are second ionisation energies endothermic or exothermic?

Endothermic

What is first electron affinity?

Enthalpy change that occurs when one electron is added to each atom in one mole of gaseous atoms to form one mole of 1- ions

What is the first electron affinity of oxygen?

O (g) + e- —> O-(g)

Are first electron affinities endothermic or exothermic?

Exothermic (for an electronegative element)

What is second electron affinity?

Enthalpy change that occurs when one electron is added to each ion in one mole of gaseous 1- ion to form one mole of 2- ions

What is the second electron affinity of oxygen?

O- (g) + e- —> O2- (g)

Are second and further electron affinities endothermic or exothermic?

Endothermic

What is standard enthalpy change of solution?

Enthalpy change that occurs when one mole of a solute dissolves in a solvent

What is the standard enthalpy change of solution of sodium chloride in water?

Na+Cl- + aq —> Na+ (aq) + Cl- (aq)

Are enthalpy change of solution endothermic or exothermic?

Can be either

What occurs when a solid ionic compounds dissolves in water?

1. Ionic lattice breaks up to form separate gaseous ions

2. Separate gaseous ions interact with polar water molecules to form hydrated aqueous ions

What is the enthalpy of hydration?

Enthalpy change that occurs when gaseous ions are dissolved in water to form one mole of aqueous ions