Solubility of many solid in a solvent increases with increase in temperature. Increase in temperature increases kinetic energy of the solute, increasing collision and weakens the intermolecular force within the solute. This makes the solute dissolve faster in their solvents.
During recrystallization, more solutes are added to the solvent at higher temperature so that a supersaturated solution is produced on cooling. As the solution cools the over saturated solute begins to precipitate out of the solution.
Recrystallization is a form of purification if solid, as the crystalline solids continue to precipitate it reject impurities are comes out as a purer solid
