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?

Word Search

Gas

Solute

Pressure

Soluble

Intermolecular

Temperature

Solvent

Molecules

Energy

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