What it does
Gases dissolve in water a little. Henry’s law says how much: the mole fraction x of a gas in the solution is proportional to the gas’s partial pressure p above it, p = KH x. Every gas has its own Henry constant KH, and a bigger KH means the gas is harder to dissolve. KH also grows with temperature, so gases dissolve less in warm water.
- A bottle of soda. Set the CO₂ pressure in a sealed bottle and its temperature. The page shows KH, the mole fraction, and how much CO₂ is dissolved in each litre in millimoles and grams, with bubbles in the bottle picture. Tap Open the bottle: the CO₂ pressure falls to the tiny amount in air, nearly all the gas has to leave, and the page says how many millilitres fizz out of each litre.
- Which gas dissolves best? A table of CO₂, oxygen and nitrogen at 1 bar at the same temperature. CO₂ is about 20 times more soluble than oxygen; nitrogen least of all.
- Divers and climbers. A diver at depth breathes air at higher pressure, so more nitrogen dissolves in the blood; rising too fast lets it out as bubbles (the bends). A climber high up breathes air at low pressure, so less oxygen dissolves (altitude sickness). The bars compare with sea level.
This fits Class 12 Chemistry: solutions (solubility of a gas in a liquid, Henry’s law and its uses, the effect of temperature). Next, see how dissolved particles change boiling and freezing points in colligative properties calculator; for the gas laws themselves, use the gas law calculator, and see the particles moving in kinetic theory.
How to use it
- Move p (CO₂ pressure in bar) and T (temperature) for the soda bottle.
- Tap Open the bottle, and Close it again to compare.
- Read the gas table, which follows the temperature you set.
- Choose Diver and set the depth, or Climber and set the altitude.
- Try the Check yourself questions.
Worked example
Soda at 2.5 bar of CO₂ and 25 °C, with KH = 1700 bar: x = 2.5 / 1700 = 1.47 × 10⁻³. One litre of water is 55.5 mol, so about 1.47 × 10⁻³ × 55.5 = 0.0818 mol = 81.8 mmol of CO₂ dissolves, which is 0.0818 × 44 = 3.6 g. Open the bottle and almost all of it must leave: about 2030 mL of gas at 1 bar from each litre.
Cool the same bottle to 5 °C and it holds 6.43 g/L; warm it to 35 °C and only 2.77 g/L. That is why warm soda goes flat faster.
Diver at 30 m: the pressure is 1 + 30/10 = 4 bar, so 4 times as much nitrogen dissolves in body water as at the surface (1.93 mmol/L instead of 0.48 mmol/L in this model). Climber at 5000 m: the air pressure is about 0.54 bar, so only about 0.54 times the sea-level oxygen dissolves.
Tips
- Henry’s law works best for gases that don’t react with water and at low pressures. CO₂ partly reacts with water to make carbonic acid, which is why soda is slightly acidic.
- Divers’ tanks for deep dives often mix in helium, which dissolves less than nitrogen.
- Aquatic life suffers in warm water because less oxygen dissolves.
FAQ
Can I use this to plan a dive? No. It is a teaching model with rounded constants; real dive planning uses tables or a dive computer and training.
Is anything saved? No. Everything runs in your browser and nothing is stored or sent.
Is this an official textbook tool? No. It is an independent practice page that follows the same school topics.
Where the numbers come from
- Henry's law p = KH x and the rise of KH with temperature (van 't Hoff form KH(T) = KH(298) e^(C(1/298 − 1/T))) are standard physical chemistry. The KH values (CO₂ 1.7, O₂ 35, N₂ 76 kbar at 25 °C) and temperature coefficients (2400, 1700, 1300 K) are rounded typical values, not copied from any one table.
- The diver and climber parts are a teaching model (1 bar per 10 m of sea water, an exponential atmosphere with an 8 km scale height, body water as plain water at 37 °C). They are not for planning dives or climbs. The maths was checked in the tests against an independent Python version.
- Drawings are fibub's own. Nothing you enter is stored or sent anywhere.
Standard scientific values, such as constants, atomic weights and melting points, are facts found in every textbook; we name where ours were checked. If you are an author or publisher and want a value, a credit or a table changed or removed, tell us and we will act quickly.
Last updated 2026-11-09.