Solids

The effects of temperature on the solubility of solids differ depending on whether the reaction is endothermic or exothermic. Using Le Chatelier's Principle, we can determine the effects of temperature in both scenarios.

First, imagine an endothermic reaction (heat is on the reactants side where the solid is). Increasing the temperature would result in stress on the reactants side from the additional heat. Le Châtelier's Principle predicts that the system would shift towards the product's side in order to alleviate this stress. By shifting towards the product's side, more of the solid is dissociated when equilibrium is again established - which equates to increased solubility.

Second, imagine an exothermic reaction (heat is on the products side where the dissociated ions from the solid are). Increasing the temperature would result in stress on the products side from the additional heat. Le Châtelier's Principle predicts that the system would shift towards the reactant's side in order to alleviate this stress. By shifting towards the reactant's side, less of the solid is dissociated when equilibrium is again established - which equates to decreased solubility.

Liquids

In the case of liquids, there is no defined trends for the effects of temperature on the solubility of liquids. As such, you will probably never encounter liquid-liquid solute-solvent mixtures in problems.

Gases

In understanding the effects of temperature on the solubility of gases, it is first important to remember that temperature is the measure of the average kinetic energy. As temperature increases, kinetic energy increases. The greater kinetic energy results in greater molecular motion of the gas particles. As a result, the gas particles dissolved in the liquid are more likely to escape to the gas phase and the existing gas particles are less likely to be dissolved. The converse is true as well. So, the trend now appears as follows : increased temperatures mean lesser solubility and decreased temperatures mean higher solubility.

Using Le Chatelier's Principle, we can better conceptualize these trends. First, note that the process of dissolving gas in liquid is usually exothermic. As such, increasing temperatures would result in stress on the product's side (since heat is on the product's side). In turn, Le Chatelier's Principle predicts that the system will shift towards the reactant's side in order to alleviate this new stress. Consequently, the equilibrium concentration of the gas particles in gaseous phase would increase - which equates to lowered solubility.

Conversely, decreasing temperatures would result in stress on the reactant's side (since heat is on the product's side). In turn, Le Châtelier's Principle predicts that the system will shift towards the product's side in order to compensate for this new stress. Consequently, the equilibrium concentration of the gas particles in gaseous phase would decrease - which equates to greater solubility.

Solids & Liquids

The effects of pressure changes on the solubility of solids and liquids are negligible.

Gases

The effects of pressure on the solubility of gases in liquids can best be described through a combination of Henry's Law and Le Châtelier Principle. Henry's Law dictates that when temperature is constant, the solubility of the gas corresponds to it's partial pressure. Consider the following formula of Henry's Law: 

\[ p = k_h \; c \]

where p is the partial pressure of the gas above the liquid, \(k_h\) is Henry's Law constant, and c is the concentrate of the gas in the liquid.

From this formula, you can see that (at a constant temperature) when the partial pressure decreases, the concentration of gas in the liquid will decrease as well - which means that solubility also decreases. Conversely, when the partial pressure increases in such a situation, the concentration of gas in the liquid will increase as well - which means that solubility also increases. Extending the implications from Henry's Law, we can now enhance our understanding of Le Châtelier's Principle in predicting the effects of pressure on the solubility of gases. Le Chatelier's Principle dictates that a system will shift in such a way as to alleviate stress.

Consider a system consisting of a gas that is partially dissolved in liquid. An increase in pressure would result in greater partial pressure (since the gas is being further compressed). This increased partial pressure means that more gas particles will enter the liquid (which means less gas above the liquid, so partial pressure decreases) in order to alleviate the stress created by the increase in pressure - which equates to greater solubility.

The converse case in such a system is also true, as a decrease in pressure equates to more gas particles escaping the liquid to compensate.

Consider the following system that is in equilibrium:

\[ CO_2 (g) + H_2O (l) \rightleftharpoons H_2CO_3 (aq) \]

What will happen to the solubility of the carbon dioxide if - 

1. Temperature is increased?
2. Pressure AND Temperature are increased?
3. Pressure is increased BUT Temperature is decreased?
4. Pressure is increased?

Solution: 

1. The reaction is exothermic, so an increase in temperature means that solubility would decrease.
2. An increase in pressure and an increase in temperature in this reaction both equate to greater solubility. Thus, the solubility would increase.
3. The change in solubility cannot be determined from the given information.
4. An increase in pressure results in more gas particles entering the liquid in order to decrease the partial pressure. Therefore, the solubility would increase.

Bob is in the business of purifying silver compounds to extract the actual silver. He is extremely frugal and hoards every penny. One day, he is finds a barrel containing a saturated solution of silver chloride. Bob has a bottle of water, a jar of table salt \(NaCl_(s)\), and a bottle of vinegar \(CH_3COOH\). Which of the 3 should Bob add to the solution to maximize the amount of solid silver chloride (so he wants to minimize the solubility of the silver chloride)?

Solution: 

Bob should add table salt to the solution. According to the common-ion effect, the additional \(Cl^-\) ions added would reduce the solubility of the silver chloride, which maximizes the amount of solid silver chloride.

Allison has always wanted to start her own carbonated drink company. Recently, she opened a factory to produce her drinks. She wants her drink to "out-fizz" all the competitors. That is, she wants to maximize the solubility of the gas in her drink. Under what conditions (high/low temperature, high/low pressure), would it best allow her to achieve this goal?

Solution: She would be able to maximize the solubility of the gas in her drink (maximize fizz) when the pressure is high and temperature is low.

Butters is trying to increase the solubility of a solid in some water. He begins to frantically stir the mixture. Should he continue stirring? Why or Why not?

Solution: He stop stop stirring. Stirring only affects how fast the system will reach equilibrium and does not affect the solubility of the solid at all.

With respect to Henry's Law, why is it ideal to open a can of soda in a low pressure environment? 

Solution: The lower pressure equates to greater solubility - therefore, the soda will stay carbonated for longer.