Intro to Henry's Law - Online Tutor, Practice Problems & Exam Prep

Henry's Law states that the solubility of a gas in a liquid is directly proportional to the partial pressure of the gas above the liquid. As pressure increases, gas solubility increases, since the gas is forced into the liquid. However, this pressure-solubility relationship does not apply to solids or liquids—only gases. Conversely, the temperature-solubility relationship indicates that as temperature rises, gas solubility decreases, exemplified by steam escaping boiling water. For solids, the opposite is true; higher temperatures increase solubility, as seen when a solid dissolves more readily in a heated solvent. Remember, solubility is the ability of a solute to dissolve in a solvent, and it varies with both pressure and temperature, affecting gases and solids differently.

Intro to Henry's Law Concept 1

Now, when it comes to Henry's law, it's important to understand that the solubility of a dissolved gas is directly proportional to the partial pressure of that gas over the liquid. So when we talk about Henry's law, we have to take into account two different relationships. Those are the pressure solubility relationship and the temperature solubility relationship.

Now here we're going to say as the pressure increases above gases that are over liquid, then the solubility of a gas increases. So all you have to think about is I have this closed container and I can apply outward pressure on it, pushing down on this piston. That puts pressure on the gases that are above the liquid. And what happens here is that added pressure forces the gases to go down into the water, making them become dissolved and thereby increase their solubility.

Now we're going to say here, changes in pressure have no effect on solids or liquids. So this is only in terms of increasing the solubility of gases if we increase the pressure on them. Now with temperature and solubility, that relationship, we're going to say as the temperature increases, then the solubility of a gas decreases. So think about it like this. You have a pot of water that you're boiling on the stove, right? That lid is closed, and if you give it enough time, what starts to happen? Steam starts to come out of the water. Well, that's gas escaping the water. It's no longer dissolved in the solvent and therefore its solubility is decreasing. Because remember, solubility is being able to dissolve a solute within a solvent.

Now we're going to say here temperature and solubility does not only affect gases, but it can also affect solids. We're going to say as the temperature increases, the solubility of a solid actually increases. So if you think you have like a hard like substance, like a rock or something in here and you boil it in there, what's going to happen? Eventually the rock's going to break apart. Breakdown. It's going to become dissolved within the solvent. So just remember, increasing the temperature on solids increases their solubility.

Intro to Henry's Law Example 1

In general, as the temperature increases, the solubility of a gas in a given liquid, So remember, we increase the temperature on a solution, the gases are going to start escaping that solution and therefore thereby decrease their solubility.

And the solubility of most solids in a given liquid will increase. So think about hard substance like a rock throwing into a boiling that of water. Over time, that rock can be broken down by those increased temperatures.

So here we're going to have decreases and then increases. So here option B would be the correct answer.

Which of the following is true for the solubility of KBr (s) and CH₃(CH₂)₃CH₃ (g) in water?

• A. Decreasing the temperature will decrease the solubility of CH₃(CH₂)₃CH₃.
• B. Increasing the pressure will decrease the solubility of KBr.
• C. Both KBr and CH₃(CH₂)₃CH₃ are completely soluble in water.
• D. Both are insoluble in water.
• E. None of the above.

Here’s what students ask on this topic:

What is Henry's Law and how does it relate to gas solubility?

Henry's Law states that the solubility of a gas in a liquid is directly proportional to the partial pressure of the gas above the liquid. Mathematically, it can be expressed as:

$C=kP$

where $C$ is the concentration of the gas in the liquid, $k$ is the Henry's Law constant, and $P$ is the partial pressure of the gas. As the pressure increases, the gas is forced into the liquid, increasing its solubility. This relationship is specific to gases and does not apply to solids or liquids.

How does temperature affect the solubility of gases and solids?

Temperature has opposite effects on the solubility of gases and solids. For gases, as temperature increases, solubility decreases. This is because higher temperatures provide more energy for gas molecules to escape from the liquid, as seen with steam escaping from boiling water. Conversely, for solids, increasing temperature generally increases solubility. Higher temperatures provide more energy to break down the solid structure, allowing it to dissolve more readily in the solvent.

Why does increasing pressure increase the solubility of gases in liquids?

Increasing pressure increases the solubility of gases in liquids because it forces more gas molecules into the liquid. When pressure is applied to a gas above a liquid, the gas molecules are pushed into the liquid, where they become dissolved. This is described by Henry's Law, which states that the solubility of a gas is directly proportional to the partial pressure of the gas above the liquid. Therefore, higher pressure results in higher gas solubility.

Does Henry's Law apply to solids and liquids?

No, Henry's Law does not apply to solids and liquids. Henry's Law specifically describes the relationship between the solubility of gases and the partial pressure of those gases above a liquid. Changes in pressure do not affect the solubility of solids or liquids. However, temperature can affect the solubility of both gases and solids, but in opposite ways: increasing temperature decreases gas solubility and increases solid solubility.

What happens to the solubility of a gas when the temperature is increased?

When the temperature is increased, the solubility of a gas decreases. Higher temperatures provide more kinetic energy to gas molecules, allowing them to escape from the liquid more easily. This is why you see steam escaping from boiling water; the gas molecules are no longer dissolved in the liquid. Therefore, as temperature rises, gas solubility decreases.