Role of Lattice Energy

(i)    Stability of ionic solids. Greater the lattice energy, greater is the stability of an ionic solid. Because more energy will be needed to pull  apart the + ve and –ve ions.

(ii)    Melting points. Salts with high lattice energies require a greater input of thermal energy to breakdown the crystal lattice. Consequently, salts have high melting points.

(iii)    Solubilities of ionic solids. The magnitude of lattice energy of a solid may give us an idea about the solubility of that substance in different solvents. Ionic solids in general are insoluble in non-polar (covalent) solvents such as carbon tetrachloride, whereas these are soluble in polar solvents, like water. For a solid to dissolve in a solvent, the strong forces of attraction between its ions (lattice energy) must be overcome. This energy can be overcome by ion solvent interaction. The solvation of ions is referred to in terms of solve-tion energy which is always negative, i.e. energy is released in the process. The amount of salvation energy depends upon the nature of ht solvent. In case of anon-polar solvents he salvation energy is small and its is not sufficient to overcome the lattice energy of the solid, thereby the substance does not dissolve. The salvation energy increases if the solvent has high dipole moment/or high Polari ability. As a general rule, we may say that for a solid to dissolve in a particular solvent its salvation energy should be greater than the lattice energy of that solid.

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