Energetics II

The enthalpy change when 1 mole of a solid ionic compound is formed from its gaseous ions under standard conditions

• measure of disorder • number of ways that energy can be shared between particles

the enthalpy change when 1 mole of gaseous ions is made from an element in its standard state.

the enthalpy change when 1 mole of gaseous 1- ions are formed from 1 mole of gaseous atoms.

• size of charge • ionic radius

• larger charge = stronger electrostatic attraction between ions • therefore, more energy needed to overcome these forces, leading to a higher melting and boiling point.

• smaller ion = stronger electrostatic attraction between ions • can also pack closer together, more energy required to overcome the stronger forces = higher boiling and melting points.

• original ionic compound (formation of which is exothermic) • enthalpy of atomisation (for all elements if needed) (endothermic) • ionisation energy of Cation (endothermic) • 1st electron affinity of Anion (endothermic) • (going right now) enthalpy of lattice (exothermic) formation.

• assume a perfect ionic model • 100%, and attractions are purely electrostatic.

• different if the compound shows covalent character - ie the cation distorts the anion slightly (kind of like they are sharing) • The higher the covalent character, the higher the larger the difference would be in the theoretical and Born Haber value. • the Born Haber value for a compound would be larger than the theoretical when the compound has some covalent character.

• the enthalpy change when 1 mole of an ionic solid dissolves in a large enough amount of water to ensure they don’t interact.

• the enthalpy change when 1 mole of an ionic crystal is formed from its constituent gaseous ions.

• when one mole of gaseous ions become hydrated such that further dilution causes no heat change.

Enthalpy change of solution = -Enthalpy of lattice formation + sum of enthalpy of hydration.

• substance more likely soluble if exothermic • substance more likely to be insoluble if endothermic (as lattice energy much larger than hydration enthalpy.)

• entropy increases as there is more disorder, as solid changes to solution and number of particles increases. • this can make the total ΔSsystem can make the ΔStotal positive even if ΔH solution is endothermic, esp at higher temps.

• your reactants and products • does not change temp or pressure • mass cannot be transferred to the surroundings • energy can be transferred to the surroundings.

• as a solid is heated up, and turns into liquid, its particles vibrate more, meaning that its entropy increases • gasses are most disordered, so have the highest enthalpy.

a positive entropy change ( ΔS’ system = +ve)

= ΣS products - ΣS reactants

J/K/mol

-ΔH reaction/T - covert ΔH to J/mol (x1000) - convert degrees to Kelvin (+273)

ΔS total = ΔS system + ΔS surrounding

• ΔS total