Intermediate Topic 301 of 1102 States of Matter & Solutions
Henry's Law
The solubility of a gas in a liquid is proportional to its partial pressure above the liquid.
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In-depth explanation of Henry's Law
Henry's law states that the solubility of a gas in a liquid is proportional to the partial pressure of that gas above the liquid, at constant temperature. It is written C = kH P, where C is the concentration of dissolved gas, P is its partial pressure, and kH is a constant characteristic of the gas and solvent. Increasing the pressure forces more gas molecules into the liquid, while lowering the pressure allows dissolved gas to escape. The law explains why carbonated drinks fizz when opened and why divers must ascend slowly to avoid decompression sickness. It applies best to dilute solutions of gases that do not react with the solvent.
Going deeper: Henry's Law
Key ideas: Formula C = kH P. For CO2 in water at 25 C, kH is about 0.034 mol/(L atm), and for O2 about 1.3 x 10^-3. A drink bottled at 2 to 4 atm of CO2 degasses when opened since air has only about 0.0004 atm. Solubility drops as temperature rises. At depth, diver tissues absorb more N2 per atmosphere.
Common mistakes and connections: The law fails for gases that react with water, such as HCl and NH3, and at high pressures. Another mistake is applying total pressure rather than the partial pressure of that gas. Different forms of kH have different units, so check them. Links to Dalton's law, temperature and solubility, and decompression sickness.
Visualization of Henry's Law
Henry's law: gas solubility is proportional to its partial pressure, which is why opening a soda bottle releases fizzing CO2. The interactive lesson shows this as a live animation or chart.
Worked example and use case
Opening a sealed soft drink lowers the pressure of carbon dioxide above the liquid, so dissolved CO2 escapes as bubbles.
Frequently asked questions about Henry's Law
What is Henry's Law?
The solubility of a gas in a liquid is proportional to its partial pressure above the liquid.
Is Henry's Law a beginner, intermediate or advanced topic?
Henry's Law is a intermediate topic in States of Matter & Solutions. It builds on the vocabulary of beginner topics in this area.
What should I learn before Henry's Law?
Study these earlier topics in States of Matter & Solutions first: Parts Per Million, Normality, Dilution.
What comes after Henry's Law?
The next topics in States of Matter & Solutions are Temperature and Solubility and Raoult's Law.
Can I practise Henry's Law with quizzes?
Yes. The interactive lesson includes a self-check question on Henry's Law, and the States of Matter & Solutions quiz draws on every topic in this area.
Where Henry's Law fits in States of Matter & Solutions
Henry's Law is topic 82 of 109 in States of Matter & Solutions.