Ionisation energy

• The?ionisation?energy?(ΔH_IE^?) is the standard enthalpy change that occurs on the removal of 1 mole of electrons from 1 mole of gaseous atoms or positively charged ions
• Ionisation energy?is always endothermic as energy is need to overcome the attraction between an electron and the nucleus
• The?first ionisation energy (ΔH_IE1^?)?is the energy required to remove one mole of electrons from 1 mole of gaseous atoms of an element to form 1 mole of 1+ ions in the gaseous phase

ΔH_IE1^?Al (g) → Al⁺?(g) + e^–? ? ? ? ? ΔH_IE1^??= +577 kJ mol^-1

• The?second ionisation energy (ΔH_IE2^?)?is the energy required to remove 1 mole of electrons from 1 mole of gaseous 1+ ions to form 1 mole of 2+ ions in the gaseous phase

ΔH_IE2^?Al⁺?(g) → Al²⁺?(g) + e^–? ? ? ΔH_IE2^??= +1820 kJ mol^-1

Enthalpy of Atomisation

• The?enthalpy of atomisation?(ΔH_at^?) is the standard enthalpy change that occurs on the formation of 1 mole of separate gaseous atoms an element in its standard state
• The ΔH_at^??is always?endothermic?as energy is always required to?break?any bonds between the atoms in the element or to break the element into its gaseous atoms
  • Since this is always an endothermic process, the enthalpy change will always have a?positive?value

Na (s) → Na (g)? ? ? ? ? ?ΔH_at^??= +108 kJ mol^?-1

?Cl (g) → Cl (g)? ? ? ? ? ΔH_at^??= +122 kJ mol^?-1

Electron Affinity

• The?electron affinity?(ΔH_EA^?) of an element is the energy change when 1 mole of electrons is gained by?1 mole?of gaseous atoms of an element to form?1 mole of gaseous ions under standard conditions
• For example, the first electron affinity of chlorine is:

Cl?(g)+ e^–?→ Cl^–?(g) ? ? ? ? ?ΔH_EA^??= -364 kJ mol^-1

• The?first electron affinity?is always?exothermic?as energy is released when electrons are attracted to the atoms
• However, the?second electron affinity?of an element can be?endothermic?as illustrated by oxygen:

O^–?(g) + e^–?→ O^2-?(g) ? ? ? ? ?ΔH_EA^??= +844 kJ mol^-1

• This is because a large force of?repulsion?must be overcome between the negatively charged ion and the second electron requiring a large input of energy

Lattice Enthalpy

• The?lattice enthalpy?(ΔH_lat^?) is defined as the standard enthalpy change that occurs on the formation of 1 mole of gaseous ions from the solid lattice
• The ΔH_lat^??is always?endothermic?as energy is always required to?break?any bonds between the ions in the lattice
  • Since this is always an endothermic process, the enthalpy change will always have a?positive?value

NaCl (s) → Na⁺?(g) + Cl^-?(g)? ? ?ΔH_lat^??= +790 kJ mol ^-1

Enthalpy of Solution?

• The?standard enthalpy change of solution (ΔH_sol^?)?is the enthalpy change when?1 mole?of an ionic substance?dissolves?in sufficient water to form an?infinitely?dilute solution
• The symbol?(aq)?is used to show that the solid is dissolved in?sufficient water
• ΔH_sol^??can be?exothermic?(negative) or?endothermic?(positive)

LiBr(s) → LiBr(aq)? ? ΔH_sol^??= -48.8 kJ mol^?-1

KCl (s) → KCI (aq)? ? ? ΔH_sol^??= +17.2 kJ mol^?-1

CaCl₂(s) → CaCl₂?(aq)? ? ? ?ΔH_sol^??= -82.8 kJ mol^?-1

Enthalpy of Hydration

• The?standard enthalpy change of hydration?(ΔH_hyd^?)?is the enthalpy change when?1 mole?of a specified?gaseous ion?dissolves?in sufficient water to form an infinitely dilute?solution

Mg^2+?(g) → Mg^2+?(aq)? ?ΔH_hyd^??= -1963 kJ mol^?-1

Br^-?(g) → Br^-?(aq)? ? ? ? ? ΔH_hyd^??= -328 kJ mol^?-1

• Hydration enthalpies are the measure of the energy that is released when there is an attraction formed between the ions and water molecules
• Hydration enthalpies are?exothermic
• The term?solvation?is used in place of hydration if water has been replaced by another solvent
• When an?ionic solid?dissolves in water, positive and negative ions are formed
• Water is a?polar?molecule with a δ- oxygen (O) atom and δ+ hydrogen (H) atoms which will form?ion-dipole attractions?with the ions present in the solution
• The oxygen atom in water will be attracted to the?positive ions?and the hydrogen atoms will be attracted to the?negative?ions

The polar water molecules will form ion-dipole bonds with the ions in solution causing the ions to become hydrated?