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.