Question

During crystallization of a pure cyclohexane the temperature stays constant until all the cyclohexane is crystallized. However, during the crystallization of a solution of naphthalene in cyclohexane the temperature gradually decreases. Why?

Answer 1

Solution :-

In the crystallization of the pure cyclohexane the phase change of the substance takes place at the constant temperature therefore the temperature remains same until all the cylohexane crystallizes,

In contrast in the crystallization of the naphthalene the temperature of the solution gradually decreases as naphthalene starts crystallizing because the phase change of the naphthalene from aqueous to solid is endothermic process means absorbing the energy from the solvent or solution therefore it causes the decrease in the temperature of the solution as naphthelene crystallizes.