AP CHEM solutions

Gas Solubility refers to the ability of a gas to dissolve in a liquid. Unlike solids and liquids, the Solubility of gases is significantly affected by pressure and Temperature. Understanding these factors is crucial for predicting and explaining gas behavior in various systems.

Calculating Gas Solubility

Using Henrys Law, we can calculate the concentration of a dissolved gas given its partial pressure and Henrys Law constant. For example, if the partial pressure of $ CO_2 $ above a soda is 2 atm and $ k_H $ for $ CO_2 $ in water at a given Temperature is 0.034 mol/L·atm, the concentration of dissolved $ CO_2 $ would be:

$ C = k_H P = (0.034 \text{ mol/L·atm}) (2 \text{ atm}) = 0.068 \text{ mol/L} $

This calculation provides a simplified model. In reality, deviations from Henrys Law can occur at higher pressures or when the gas is highly soluble.

Factors Affecting Gas Solubility

1. Pressure: Henrys Law

2. Temperature

Generally, the Solubility of gases in liquids decreases with increasing Temperature. As Temperature rises, the kinetic energy of the gas molecules increases, allowing them to overcome the intermolecular forces holding them in solution and escape into the gaseous phase. This is why a warm soda goes flat faster than a cold one.

3. Nature of the Gas and Solvent

The chemical nature of both the gas and the solvent plays a role in Solubility. Polar gases tend to dissolve better in polar solvents (like water), while nonpolar gases dissolve better in nonpolar solvents (like hydrocarbons). This is due to the principle of “like dissolves like,” where similar intermolecular forces between solute and solvent facilitate dissolution. For instance, $ CO_2 $ (a slightly polar molecule) is more soluble in water than $ O_2 $ (a nonpolar molecule). intermolecular forces

4. Presence of Other Solutes

The presence of other dissolved substances in the solvent can affect the Solubility of a gas. These interactions can either enhance or hinder the gas’s Solubility, depending on the specific solute-solute and solute-solvent interactions.