- 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.
- 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).
- 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?