Tackk will be shutting down on 9.30.17 - Export your Tackks

# Gas Solubility

Temperature:
•   Gases are more soluble at low temperatures
•   Hotter it gets, the less likely it is to dissolve in solutions
•   For gas to dissolve in a solvent (substance that can dissolve another substance) such as water, a “pocket has to open in the solvent for the gas molecule to fit into.
• Energy is absorbed to open a pocket in the solvent
•       - Solvent molecules attract each other
•       - Pulling the molecules apart to make a void requires energy, heat is absorbed during this process (for most solvents)
• ** Water is special because it already has pockets at/near room temperature
• Energy is released when a gas molecule enters a solvents pocket
• More heat is released during gas placement then in pocket formation
• - Inter-molecular attractions between the gas molecules and solvent molecules lower its energy and heat is released
• [Stronger the attraction, the more heat is released]
•   There is usually a net release of heat when gases are dissolved in water
• Le Chatelier’s principle= gas solubility decreases when temperature rises. Thus, gases become less soluble in water as the temperature increases.
• An increase in temperature always favors the endothermic reaction
• The reverse reaction is favored, and the reaction shifts to the left to redistribute that excess heat.
• Some of the aqueous oxygen dissolved in the water is forced out of solution and back into the atmosphere
•   Heat and drought lower river levels and drive dissolved oxygen out of the water, leading to fish kills.
• Also why you put sodas in the refrigerator to keep them from going flat, the carbon dioxide is more soluble at low temperatures in the refrigerator.

Pressure:

• Gases are more soluble at higher pressures. Pressure is not a factor for solubility of solids in solution.
• As pressure goes up gas solubility goes up
• As volume goes up pressure goes down
• Decreasing volume increases pressure
• Shoves gas into solution
• Henry’s Law: C=kP
• C = concentration of the dissolved gas
• k = a constant unique to that solution
• P = partial pressure of the gas above the solution
• The law basically states the amount of a gas dissolved in a solution is directly proportional to the pressure of the gas above the solution
• Henry’s Law is obeyed most accurately for dilute solutions of gases that do not dissociate in or react with the solvent (usually water).

# Quiz

• 1. Gases are most soluble at

A. Low Temperatures and High Pressures

B. High Temperatures and Low Pressures

C. Low Temperatures and Low Pressures

D. High Temperatures and High Pressures

• 2. Most of these reactions are (exothermic/endothermic)
• 3. How are pockets formed in a solvent and for what reasons are these pockets formed?
• 4. Give an example that proves these rules of gas solubility.
• 5. How do you find the change in temperature?

Gas

Solute

Pressure

Soluble

Intermolecular

Temperature

Solvent

Molecules

Energy