Problem 69 - Chemistry for Allied Health

Question

Under which set of conditions is the solubility of a gas in a liquid the greatest? a. low temperature and low pressure b. low temperature and high pressure c. high temperature and low pressure d. high temperature and high pressure

Step-by-Step Solution

Answer

Option b: low temperature and high pressure.

Step 1: Understand the Effect of Temperature

The solubility of a gas in a liquid typically decreases with an increase in temperature. This is because higher temperatures provide more energy for the gas molecules to escape from the liquid.

Step 2: Understand the Effect of Pressure

According to Henry's Law, the solubility of a gas in a liquid is directly proportional to the pressure of the gas above the liquid. Higher pressure forces more gas molecules into the solution, increasing solubility.

Step 3: Combine Temperature and Pressure Effects

To maximize the solubility of a gas in a liquid, you want conditions that keep the gas dissolved. Low temperatures reduce the kinetic energy of the gas molecules, preventing them from escaping, while high pressures push more gas into the liquid.

Step 4: Analyze the Choices

From the problem options, low temperature and high pressure (option b) best support the greatest solubility of a gas in a liquid by minimizing escape and maximizing dissolution of gas molecules.

Key Concepts

Henry's Law

Henry's Law is a fundamental principle in chemistry that helps us understand the behavior of gases dissolved in liquids. It says that the amount of gas that can dissolve in a liquid at a constant temperature is directly proportional to the partial pressure of the gas above the liquid. This means if you increase the pressure of the gas in contact with the liquid, the solubility of the gas increases. Mathematically, this can be expressed as \( C = kP \), where \( C \) is the solubility of the gas, \( k \) is Henry's Law constant for the specific gas-liquid system, and \( P \) is the partial pressure of the gas.

For example, consider a soda can. When sealed, it contains carbon dioxide at high pressure, allowing more CO₂ to be dissolved in the liquid. Once opened, the pressure drops, and the gas escapes, decreasing its solubility.

Temperature Effects on Solubility

Temperature has a significant impact on the solubility of gases in liquids. In general, as the temperature increases, the solubility of a gas decreases.

• At higher temperatures, gas molecules gain more kinetic energy.
• This energy enables them to escape more easily from the liquid.
• Hence, less gas remains dissolved.

When thinking about carbonated beverages, they often become less fizzy and more flat if left out in the warm environment because the CO₂ gas easily escapes. Conversely, in colder conditions, the solubility of the gas increases, allowing more gas to remain in the solution.

This behavior is an essential factor in many industrial processes, especially in maintaining the efficiency of reactions where gases need to be dissolved in liquids.

Pressure Effects on Solubility

The effect of pressure on gas solubility is closely related to Henry's Law. Increasing the pressure of a gas over a liquid enhances the solubility of that gas in the liquid. Here's why this happens:

• Higher pressure means more gas molecules are pushed into the liquid.
• As more molecules accumulate, more of them dissolve until a new equilibrium is reached.
• This continuous influx maximizes the amount of dissolved gas.

This concept is widely utilized in carbonated drinks, where CO₂ is dissolved under high pressure. Similarly, in deep-sea conditions where pressure is high, gases dissolve more readily, affecting marine life adaptations.

Understanding the pressure effects is crucial for fields like scuba diving, where pressure changes can dramatically influence the solubility of gases in body fluids.