Henry's Law
Gas solubility in liquids, KH constants, and real-world consequences
A scuba diver breathes compressed air at 30 m depth where pressure is ~4 atm. Nitrogen dissolves into her blood and tissues at 4× the surface concentration. When she surfaces too quickly, she experiences severe joint pain, paralysis, and can die. What happens to the dissolved nitrogen when pressure suddenly drops — and why does surfacing slowly prevent this?
The fizz in your soda is compressed dissolved under pressure. The bottle is sealed at ~2.5–4 atm of pressure. The moment you open the cap, pressure drops to 1 atm — and Henry's law predicts exactly how much will escape. Warm soda fizzes more violently because gas solubility decreases with temperature — the same amount of pressure drop releases more gas from a warm bottle. Soda manufacturers solve this by refrigerating product before sale. Every fizz is a demonstration of Henry's law.
Henry's Law Statement
Henry's Law: At constant temperature, the solubility of a gas in a liquid is directly proportional to the partial pressure of the gas above the liquid.
where:
- = partial pressure of the gas above the solution
- = mole fraction of the dissolved gas in the solution
- = Henry's law constant (units: pressure, e.g. bar or Pa)
Important: has a large value for gases that are less soluble (like , ). A small means the gas dissolves easily at low pressure (like ).
Henry's Law constants (KH) for common gases in water at 298 K
| Gas | KH (kbar) | Implication |
|---|---|---|
| 46.82 | Moderately insoluble — enough for aquatic life | |
| 76.48 | Very insoluble — causes "the bends" at depth | |
| 1.67 | Most soluble of common gases — makes carbonation possible | |
| 144.97 | Extremely insoluble — used in diving gas mixes to avoid narcosis |
Limitations of Henry's Law
Henry's law holds strictly only under these conditions:
- Low pressure — the gas must not interact strongly with the solvent
- Low concentration of dissolved gas
- The gas must not react with the solvent — ionises in water (), so it does not obey Henry's law. partially reacts () so it shows deviations at higher concentrations.
- The gas must not associate in solution
AI Generation Prompt
Henry's Law diagram. A sealed container divided horizontally: gas phase above, liquid phase below. Show three versions side by side at increasing pressures (0.5 atm, 1 atm, 2 atm). At 0.5 atm: few green dots (CO₂ molecules) in gas, very few dissolved in liquid. At 1 atm: twice as many green dots in gas, twice as many dissolved. At 2 atm: four times as many green dots in gas, four times dissolved. Arrows showing gas molecules entering liquid (dissolution). Label each panel with its pressure and corresponding mole fraction (x = 0.005, x = 0.01, x = 0.02). Show the linear p vs x graph below. Dark background, orange accent labels, clean technical illustration style.
Problem
If the Henry's law constant for in water is Pa at 298 K, find the mole fraction of dissolved in water when the pressure above the solution is Pa.
Q1.Henry's law states that at constant temperature, the solubility of a gas in a liquid is:
A scuba diver breathes compressed air at 30 m depth where pressure is ~4 atm. Nitrogen dissolves into her blood and tissues at 4× the surface concentration. When she surfaces too quickly, she experiences severe joint pain, paralysis, and can die. What happens to the dissolved nitrogen when pressure suddenly drops — and why does surfacing slowly prevent this?
The fizz in your soda is compressed dissolved under pressure. The bottle is sealed at ~2.5–4 atm of pressure. The moment you open the cap, pressure drops to 1 atm — and Henry's law predicts exactly how much will escape. Warm soda fizzes more violently because gas solubility decreases with temperature — the same amount of pressure drop releases more gas from a warm bottle. Soda manufacturers solve this by refrigerating product before sale. Every fizz is a demonstration of Henry's law.
Henry's Law Statement
Henry's Law: At constant temperature, the solubility of a gas in a liquid is directly proportional to the partial pressure of the gas above the liquid.
where:
- = partial pressure of the gas above the solution
- = mole fraction of the dissolved gas in the solution
- = Henry's law constant (units: pressure, e.g. bar or Pa)
Important: has a large value for gases that are less soluble (like , ). A small means the gas dissolves easily at low pressure (like ).
Henry's Law constants (KH) for common gases in water at 298 K
| Gas | KH (kbar) | Implication |
|---|---|---|
| 46.82 | Moderately insoluble — enough for aquatic life | |
| 76.48 | Very insoluble — causes "the bends" at depth | |
| 1.67 | Most soluble of common gases — makes carbonation possible | |
| 144.97 | Extremely insoluble — used in diving gas mixes to avoid narcosis |
Limitations of Henry's Law
Henry's law holds strictly only under these conditions:
- Low pressure — the gas must not interact strongly with the solvent
- Low concentration of dissolved gas
- The gas must not react with the solvent — ionises in water (), so it does not obey Henry's law. partially reacts () so it shows deviations at higher concentrations.
- The gas must not associate in solution
AI Generation Prompt
Henry's Law diagram. A sealed container divided horizontally: gas phase above, liquid phase below. Show three versions side by side at increasing pressures (0.5 atm, 1 atm, 2 atm). At 0.5 atm: few green dots (CO₂ molecules) in gas, very few dissolved in liquid. At 1 atm: twice as many green dots in gas, twice as many dissolved. At 2 atm: four times as many green dots in gas, four times dissolved. Arrows showing gas molecules entering liquid (dissolution). Label each panel with its pressure and corresponding mole fraction (x = 0.005, x = 0.01, x = 0.02). Show the linear p vs x graph below. Dark background, orange accent labels, clean technical illustration style.
Problem
If the Henry's law constant for in water is Pa at 298 K, find the mole fraction of dissolved in water when the pressure above the solution is Pa.
Q1.Henry's law states that at constant temperature, the solubility of a gas in a liquid is: