# How does solubility change with temperature changes?

Jun 1, 2014

Usually, increasing the temperature increases the solubility of solids and liquids. Increasing the temperature always decreases the solubility of gases.

#### Explanation:

When you add a solute to a solvent, the kinetic energy of the solvent molecules overcomes the attractive forces among solute particles.

The solute particles leave the surface of the solid and move into the dissolved (aqueous) phase. In the image below the mass of grey (-) balls and green (+) balls represent a salt crystal. As the salt dissolves, the positive and negative ions are pulled apart and become surrounded by water molecules.

If we heat the solvent, the average kinetic energies of its molecules increases. Hence, the solvent is able to dislodge more particles from the surface of the solute.

Thus, increasing the temperature increases the solubilities of substances. For example, sugar and salt are more soluble in water at higher temperatures.

But, as the temperature increases, the solubility of a gas in a liquid decreases. As temperature increases, the average kinetic energy of the gas molecules increases.

As a result, the gas molecules dissolved in the liquid are more likely to escape to the gas phase and not return.

Here is an experiment which demonstrates this concept.

Video from: Noel Pauller

Oct 17, 2015

It depends.

#### Explanation:

The best way to determine the solubility of solid is by experiment.

While it is difficult to predict the solubility of solids, however there some correlation between the solubility of a solute and $\Delta {H}_{s o l u t i o n}$, that's why we can discuss the depends on temperature as follows.

The solubility of solutes in solvents could be increased or decreased by increasing or decreasing temperature, this depends if the dissolution of the substrate is exothermic or endothermic.

Exothermic dissolution : The increase in temperature will decrease the solubility.

Think "Le Châtelier's Principle".

$S o l u t e + S o l v e n t r i g h t \le f t h a r p \infty n s S o l u t i o n + H e a t$

When heat is added the equilibrium will shift to the left which will decrease the solubility.

Endothermic dissolution: The increase in temperature will increase the dissolution.

$S o l u t e + S o l v e n t + H e a t r i g h t \le f t h a r p \infty n s S o l u t i o n$ Image Source: Zumdahl textbook