Intro to Henry's Law: Videos & Practice Problems

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 in liquids?

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. This means that when the pressure of a gas over a liquid increases, more gas molecules are forced into the liquid, increasing its solubility. Mathematically, Henry's Law can be expressed as $C=kP$, where $C$ is the concentration of the dissolved gas, $k$ is Henry's law constant, and $P$ is the partial pressure of the gas. This principle is important in understanding phenomena like carbonated beverages, where increased pressure keeps more CO₂ dissolved in the liquid.

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

According to Henry's Law and related solubility principles, as temperature increases, the solubility of gases in liquids decreases. This happens because higher temperatures give gas molecules more kinetic energy, making them more likely to escape from the liquid into the gas phase. For example, when water is heated and begins to boil, dissolved gases escape as bubbles or steam, reducing solubility. This is why warm soda loses its fizz faster than cold soda. Therefore, temperature and gas solubility have an inverse relationship: increasing temperature lowers gas solubility.

Why does increasing pressure increase the solubility of gases but not solids or liquids?

Increasing pressure increases the solubility of gases because it forces more gas molecules into the liquid phase, as described by Henry's Law. The gas molecules are compressed and pushed into the solvent, increasing their concentration. However, solids and liquids are largely incompressible, so changes in pressure do not significantly affect their solubility. The interactions between solid or liquid solutes and solvents depend more on temperature and chemical properties rather than pressure. Thus, pressure changes mainly influence gas solubility, not solids or liquids.

How does temperature affect the solubility of solids in liquids?

Unlike gases, the solubility of solids in liquids generally increases as temperature rises. When a solid is heated in a solvent, the increased thermal energy helps break down the solid's structure, allowing more solute particles to dissolve. For example, sugar dissolves more readily in hot water than in cold water. This is because higher temperatures increase molecular motion, enhancing the interaction between solute and solvent molecules. Therefore, temperature and solid solubility have a direct relationship: increasing temperature increases the solubility of solids.

Can Henry's Law be applied to explain why soda goes flat faster when warm?

Yes, Henry's Law helps explain why soda goes flat faster when warm. Soda contains dissolved carbon dioxide (CO₂) gas under pressure. When the soda is warm, the solubility of CO₂ decreases because higher temperatures reduce gas solubility. As a result, CO₂ escapes from the liquid more quickly, causing the soda to lose its fizz. Additionally, opening the bottle reduces pressure, further decreasing CO₂ solubility. Thus, both increased temperature and decreased pressure cause soda to go flat faster, consistent with Henry's Law and temperature-solubility relationships.