Henry's Law says that at constant temperature, more gas dissolves in a liquid when the gas's partial pressure above the liquid is higher. In Physical Science, it explains gas solubility in solutions.
Henry's Law is the rule in Physical Science that tells you how much gas will dissolve in a liquid at a fixed temperature. The basic idea is simple: if the partial pressure of a gas above a liquid goes up, more of that gas can stay dissolved in the liquid. If the pressure drops, dissolved gas tends to leave the liquid and escape as bubbles.
You can write it as C = kH × P, where C is the concentration of the dissolved gas, P is the gas's partial pressure, and kH is Henry's Law constant. That constant is different for different gases and different liquids, so not every gas dissolves equally well. Carbon dioxide, oxygen, and nitrogen all behave a little differently because their interactions with the liquid are not the same.
This law is about equilibrium between gas particles in the air space and gas particles in the liquid. At equilibrium, gas molecules are moving both ways, into the liquid and out of it, at equal rates. When pressure increases, more gas molecules are pushed into the liquid phase until a new balance is reached.
A common classroom example is soda. Inside a sealed bottle, carbon dioxide is under high pressure, so more of it stays dissolved. When you open the bottle, the pressure above the liquid drops, the equilibrium shifts, and carbon dioxide comes out as bubbles. That is Henry's Law in action.
Temperature matters too. Warm liquids usually hold less dissolved gas than cold liquids, which is why soda goes flat faster when warm and why fish can struggle in warm water that contains less dissolved oxygen. In Physical Science, this law connects pressure, solubility, and real-world mixtures without needing advanced chemistry to see the pattern.
Henry's Law shows up any time a gas and a liquid are interacting, so it connects straight to the solutions and solubility unit in Physical Science. It gives you a reason why changing pressure changes what stays dissolved, instead of treating solubility like a fixed number.
The law also explains a lot of everyday and environmental situations. Carbonated drinks, scuba diving, and dissolved oxygen in lakes all make more sense once you see how pressure controls gas solubility. A warmer pond holding less oxygen is not just trivia, it is a real example of a gas-liquid balance changing with conditions.
This term also builds your skill at reading cause and effect in science. If pressure increases, dissolved gas usually increases. If pressure drops, gas escapes. That pattern shows up in diagrams of sealed containers, opening bottles, and pressure-change questions, so knowing Henry's Law helps you predict what happens instead of guessing.
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Visual cheatsheet
view gallerySolubility
Henry's Law is one specific way to think about solubility, but only for gases dissolving in liquids. In Physical Science, solubility is the broader idea of how much of a substance can dissolve. Henry's Law gives you the pressure part of the story, which is why it is so useful for soda, oxygen in water, and other gas-liquid mixtures.
Partial Pressure
Partial pressure is the amount of pressure contributed by one gas in a mixture of gases. Henry's Law uses that number directly, because the dissolved amount depends on the gas's pressure above the liquid. If the partial pressure changes, the amount of gas that can stay in solution changes too.
Gas-Liquid Equilibrium
Henry's Law describes what the equilibrium looks like when gas molecules move between the air and a liquid. At equilibrium, gas is still moving both directions, but the overall concentration stays steady. If pressure changes, the equilibrium shifts until a new balance is reached.
colligative properties
Colligative properties deal with how dissolved particles change a solution, especially through particle number rather than identity. Henry's Law is not one of those properties, but both ideas connect to solutions and concentration. Seeing the difference helps you avoid mixing up gas solubility with freezing point or boiling point changes.
A quiz question might give you a sealed soda bottle, an opened bottle, or warm water versus cold water and ask what happens to gas solubility. Your job is to use the pressure relationship: higher partial pressure means more gas dissolves, and lower pressure means gas leaves the liquid. You may also need to read a graph, identify which sample has more dissolved gas, or explain why bubbles form after the pressure drops. If a problem gives a Henry's Law constant, plug values into C = kH × P and watch the units carefully. For short-response questions, name the gas, the pressure change, and the direction of the solubility change instead of just saying 'it changes.'
Henry's Law and the solubility product constant both deal with dissolved substances, but they are not the same. Henry's Law applies to gases dissolved in liquids and ties solubility to partial pressure. The solubility product constant, or Ksp, applies to slightly soluble ionic solids dissolving into ions and is based on an equilibrium expression, not gas pressure.
Henry's Law says gas solubility in a liquid increases when the gas's partial pressure above the liquid increases.
The relationship is written as C = kH × P, where the constant depends on the gas and the liquid.
A sealed soda bottle keeps more carbon dioxide dissolved than an opened one because the pressure is higher.
Warm liquids usually hold less dissolved gas than cold liquids, which is why soda goes flat faster in warmth and aquatic life can be affected.
This law is about gas-liquid equilibrium, so it is most useful when a gas can move in and out of a liquid.
Henry's Law says that at constant temperature, the amount of gas dissolved in a liquid is directly proportional to the partial pressure of that gas above the liquid. In Physical Science, it is the main rule for predicting gas solubility in solutions. It explains why pressure changes can make bubbles form or disappear.
Soda is bottled under high pressure, so a lot of carbon dioxide stays dissolved in the liquid. When you open the bottle, the pressure above the soda drops, so the gas is no longer as soluble and escapes as bubbles. That fizz is the gas moving toward a new equilibrium.
Usually no, higher temperature lowers the solubility of gases in liquids. That is why warm soda loses fizz faster than cold soda and why warm water can hold less dissolved oxygen. Pressure still matters, but temperature changes the balance too.
Solubility is the general idea of how much of a substance can dissolve, while Henry's Law gives the pressure relationship for gases in liquids. So Henry's Law is a specific solubility rule, not the whole topic. It focuses on partial pressure and gas-liquid equilibrium.