22.3 factors affecting lattice enthalpy and hydration

effect of increasing ionic size on lattice enthalpy

• ionic radius increases

• attraction between ions decreases

• lattice enthalpy less negative

• melting point decreases

effect of increasing ionic charge on lattice enthalpy

• ionic charge increases

• attraction between ions increases

• lattice enthalpy becomes more negative

• melting point increases

effect on increasing ionic size on hydration enthalpy

• ionic radius increases

• attraction between ion and water molecules decreases

• hydration enthalpy less negative

effect of ionic charge on hydration enthalpy

• ionic charge increases

• attraction with water molecules increases

• hydration enthalpy becomes more negative

predicting solubility

• to dissolve an ionic compound in water, the attraction between the ions in the ionic lattice must be overcome

• this requires a quantity of energy equal to the lattice enthalpy

• if the sum of the hydration enthalpies is larger than the magnitude of the lattice enthalpy, the overall enthalpy change (enthalpy change of solution) will be exothermic and the compound should dissolve

• solubility also depends on temperature and entropy