Henry's Law
Relates the partial pressure of a gas above a liquid to its mole fraction in the solution.
What is Henry's Law?
The proportionality constant in Henry's Law, which relates the partial pressure of a gas to its mole fraction (or concentration) in a liquid at a specific temperature. It is specific to the gas-solvent pair and temperature.
Key formula / rule: Henry's Law
Key points
- Understand the relationship between gas pressure and solubility.
- Apply Henry's Law to solve quantitative problems.
- Identify the factors affecting the solubility of gases.
- Recognize the limitations and applications of Henry's Law.
Common exam trap
Confusing partial pressure with total pressure.
Definitions
- Term
Henry's Law Constant (kH)
- Meaning
The proportionality constant in Henry's Law, which relates the partial pressure of a gas to its mole fraction (or concentration) in a liquid at a specific temperature. It is specific to the gas-solvent pair and temperature.
- Term
Partial Pressure
- Meaning
The pressure exerted by a single gas in a mixture of gases, or the pressure exerted by a dissolved gas above a liquid solution.
Learning objectives
Understand the relationship between gas pressure and solubility.
Apply Henry's Law to solve quantitative problems.
Identify the factors affecting the solubility of gases.
Recognize the limitations and applications of Henry's Law.
Formulae
- Name
Henry's Law
- Note
Where P is the partial pressure of the gas, x is the mole fraction of the gas in the solution, and kH is the Henry's Law constant. This form is commonly used when solubility is expressed as mole fraction.
- Expression
P = kH * x
- Name
Henry's Law (alternative form)
- Note
Where C is the concentration of the gas in the solution (e.g., molarity) and P is the partial pressure of the gas. Note that the value and units of kH will differ from the first form.
- Expression
C = kH * P
Prerequisites
Partial Pressure
Mole Fraction
Solubility
Ideal Solutions
Common mistakes
Confusing partial pressure with total pressure.
Assuming the law holds at very high gas concentrations or extreme temperatures.
Incorrectly applying the formula when the gas reacts with the solvent.
Forgetting that kH is specific to the gas-solvent-temperature combination.
Keywords
Henry's Law
Gas Solubility
Partial Pressure
Mole Fraction
Henry's Law Constant
Physical Chemistry
Solutions
Practice preview
If the Henry's law constant for oxygen in water at 25°C is 1.2 x 10^4 atm, what is the mole fraction of dissolved oxygen in water when the partial pressure of oxygen above the water is 0.2 atm?…
hard
Consider the dissolution of CO2 in water. If the partial pressure of CO2 is doubled, how will the mole fraction of dissolved CO2 change, assuming temperature and other conditions remain constant?…
medium
Which of the following is the correct mathematical expression for Henry's law?…
easy