Intro to Henry's Law: Study with Video Lessons, Practice Problems & Examples

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. 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 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 a hard substance like a rock or something in here, and you boil it in there, what's gonna happen? Eventually, the rock is gonna 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. And the solubility of most solids in a given liquid will increase. So, think about a hard substance like a rock thrown 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. Here, 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 the pressure of the gas above the liquid increases, the solubility of the gas in the liquid also increases. This principle is crucial in various chemical processes, such as carbonation of beverages and gas exchange in biological systems.

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 phase into the gas phase. For example, when you heat water, dissolved gases like oxygen and carbon dioxide are less soluble and tend to escape, which is why you see bubbles forming. This relationship is important in understanding phenomena such as the reduced oxygen levels in warm water bodies, which can affect aquatic life.

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 pressure is applied to a gas above a liquid, it compresses the gas molecules, making them more likely to collide with the liquid surface and dissolve. This is described by Henry's Law, which states that the solubility of a gas is directly proportional to its partial pressure. This principle is used in various applications, such as in carbonated beverages, where CO₂ is dissolved in the liquid under high pressure.

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 and liquids. However, temperature changes can affect the solubility of both gases and solids. For gases, increasing temperature decreases solubility, while for solids, increasing temperature generally increases solubility. Understanding these distinctions is important for various chemical processes and reactions, especially those involving solutions and equilibrium.

What are some practical applications of Henry's Law?

Henry's Law has several practical applications in both everyday life and industrial processes. One common example is the carbonation of beverages, where CO₂ is dissolved in liquid under high pressure to create fizzy drinks. Another application is in scuba diving, where understanding gas solubility is crucial to prevent decompression sickness. In environmental science, Henry's Law helps explain the behavior of gases in natural water bodies, affecting aquatic life and water quality. Additionally, it is used in chemical engineering processes such as gas purification and the design of reactors.