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 gas's partial pressure above the liquid. Increasing pressure enhances gas solubility, while higher temperatures decrease it. For solids, increased temperature boosts solubility. This relationship is crucial for understanding gas behavior in solutions and the impact of temperature on solute dissolution. Remember, pressure changes do not affect solids or liquids, emphasizing the unique behavior of gases in solution dynamics.

Intro to Henry's Law Concept 1

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 you're going to say, as the pressure increases above gases that are over the 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? The 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 substance like a rock or something in there, and you boil it in there, what's going to happen? Eventually, the rock is going to break apart, break down. 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 decreases. Remember, when we increase the temperature of a solution, the gases are going to start escaping from that solution and thereby decrease their solubility. Conversely, the solubility of most solids in a given liquid will increase. So think about a hard substance like a rock; throw it into boiling water. Over time, that rock can be broken down by those increased temperatures. So here, we're going to have decreases and then increases. Therefore, option B would be the correct answer.

Which of the following is true for the solubility of NaCl (s) and CH₄ (g) in water?  

• A. Increasing the temperature will increase the solubility of CH₄.
• B. Increasing the temperature will decrease the solubility of NaCl.
• C. Both NaCl and CH₄ are quite soluble in water.
• D. Neither NaCl nor CH₄ are soluble 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 that 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. This means that if you increase the pressure of the gas above the liquid, more gas will dissolve in the liquid. Conversely, if the pressure decreases, the gas solubility will also decrease.

How does temperature affect the solubility of gases according to Henry's Law?

According to Henry's Law, the solubility of gases in a liquid decreases as the temperature increases. This is because higher temperatures provide more kinetic energy to gas molecules, making them more likely to escape from the liquid into the gas phase. For example, when you heat water, you observe steam, which is gas escaping from the liquid. Therefore, increasing temperature reduces the solubility of gases in liquids.

Why does increasing pressure increase the solubility of a gas in a liquid?

Increasing pressure increases the solubility of a gas in a liquid because it forces more gas molecules into the liquid phase. When you apply pressure to a gas above a liquid, you effectively push more gas molecules into the liquid, where they become dissolved. This is why carbonated beverages are bottled under high pressure to keep the carbon dioxide dissolved in the liquid. When the pressure is released, such as when you open the bottle, the gas escapes, and the beverage becomes flat.

Does Henry's Law apply to solids and liquids?

No, Henry's Law specifically applies to gases. Changes in pressure do not affect the solubility of solids or liquids. However, temperature changes can affect the solubility of both solids and gases. For solids, increasing the temperature generally increases their solubility in a liquid. For gases, increasing the temperature decreases their solubility. This distinction is important for understanding the unique behavior of gases in solution dynamics compared to solids and liquids.

What is the relationship between temperature and the solubility of solids?

The solubility of solids in a liquid generally increases with an increase in temperature. When you heat a solution, the increased kinetic energy helps break down the solid particles, allowing them to dissolve more readily in the solvent. For example, sugar dissolves more quickly in hot water than in cold water. This is because the higher temperature provides the energy needed to overcome the forces holding the solid particles together, making them more soluble.