BackGas Solubility and Henry's Law: Pressure and Temperature Effects
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Henry's Law and Gas Solubility
Introduction to Gas Solubility
The solubility of a dissolved gas in a liquid is directly proportional to the partial pressure of that gas over the liquid. This relationship is described by Henry's Law, which is fundamental in understanding how gases dissolve in solutions, especially in biological and environmental contexts.
Henry's Law: The amount of gas that dissolves in a liquid is proportional to the pressure of the gas above the liquid.
Formula:
C = concentration of dissolved gas
k_P = Henry's Law constant (depends on gas and solvent)
P = partial pressure of the gas
Pressure–Solubility Relationship
Increasing the pressure of a gas above a liquid increases the solubility of that gas in the liquid. This is because more gas molecules are forced into the solution.
Key Point: As pressure increases, the solubility of a gas increases.
Solids and Liquids: Changes in pressure have no significant effect on the solubility of solids or liquids in a solvent.
Example: Carbonated beverages are bottled under high pressure to increase the solubility of CO2 gas.
Temperature–Solubility Relationship
The effect of temperature on solubility depends on the type of solute. For gases, increasing temperature generally decreases solubility, while for most solids, increasing temperature increases solubility.
Key Point (Gases): As temperature increases, the solubility of a gas decreases.
Key Point (Solids): As temperature increases, the solubility of most solids increases.
Example: Warm soda loses its fizz faster than cold soda because CO2 is less soluble at higher temperatures.
Summary Table: Effects of Pressure and Temperature on Solubility
Factor | Gas Solubility | Solid Solubility |
|---|---|---|
Pressure | Increases with higher pressure | No significant effect |
Temperature | Decreases with higher temperature | Increases with higher temperature |
Practice Application
Question: Which of the following is true for the solubility of NaCl (s) and CH4 (g) in water?
a) Increasing the temperature will increase the solubility of CH4.
b) Increasing the temperature will decrease the solubility of CH4. (Correct)
c) Both NaCl and CH4 are quite soluble in water.
d) Neither NaCl nor CH4 are soluble in water.
e) None of the above.
Explanation: Increasing temperature decreases the solubility of gases like CH4, but increases the solubility of most solids like NaCl.
Key Terms
Solubility: The maximum amount of solute that can dissolve in a solvent at a given temperature and pressure.
Partial Pressure: The pressure exerted by a single component of a mixture of gases.
Henry's Law Constant (kP): A proportionality constant specific to each gas-solvent pair.
Additional info: The notes infer the general rules for solubility of gases and solids with respect to temperature and pressure, and provide a practice question for application.
