Intro to Henry's Law: Videos & Practice Problems

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.

Henry's Law Solubility

Henry's law describes the relationship between the solubility of a gas in a liquid and the partial pressure of that gas above the liquid. According to this law, the solubility of a dissolved gas is directly proportional to its partial pressure. This relationship can be understood through two key aspects: the pressure solubility relationship and the temperature solubility relationship.

When pressure is applied to a closed container with a liquid and gas, the solubility of the gas increases. For instance, if you imagine a piston pushing down on the gas above the liquid, the increased pressure forces more gas molecules into the liquid, enhancing their solubility. It is crucial to note that changes in pressure do not affect the solubility of solids or liquids; this principle specifically applies to gases.

On the other hand, temperature also plays a significant role in solubility. As temperature rises, the solubility of a gas decreases. A practical example is boiling water in a closed pot: as the water heats up, gas molecules escape as steam, indicating that their solubility in the water is diminishing. This phenomenon highlights that solubility refers to the ability of a solute to dissolve in a solvent.

Conversely, the effect of temperature on solids is different. As temperature increases, the solubility of solids typically increases as well. For example, if a solid substance, like a rock, is placed in boiling water, it will eventually break down and dissolve in the solvent. Thus, while higher temperatures decrease the solubility of gases, they enhance the solubility of solids.

Henry's Law Example

Understanding the relationship between temperature and solubility is crucial in chemistry. Generally, as temperature increases, the solubility of gases in liquids decreases. This phenomenon occurs because higher temperatures provide gas molecules with more energy, allowing them to escape from the liquid more easily. For instance, when you heat a carbonated beverage, the gas bubbles start to form and escape, leading to a decrease in gas solubility.

Conversely, the solubility of most solids in liquids tends to increase with rising temperatures. This can be illustrated by considering a solid substance, such as a rock, placed in boiling water. The increased temperature enhances the kinetic energy of the water molecules, which can break down the solid over time, leading to greater solubility.

In summary, the key takeaway is that while the solubility of gases decreases with increasing temperature, the solubility of solids generally increases. This dual behavior highlights the complex interactions between temperature and solubility in different states of matter.

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.

Answer: (E)

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.