Factors Affecting Solubility of Gases - NEET Notes, Formula & Common Mistakes

What NEET Asks

• Conceptual questions on effects of temperature and pressure on gas solubility are common.
• Direct applications of Henry's Law (p = K_H * x) for calculations involving mole fraction or partial pressure.
• Comparison of solubility for different gases or at varying conditions. Expect 1-2 questions from the Solutions chapter.

Key Points

• Temperature Effect: Solubility of gases in liquids decreases with increasing temperature. This is because dissolution of gases is generally an exothermic process (ΔH < 0), favoring the reverse (undissolved gas) at higher temperatures.
• Pressure Effect (Henry's Law): Solubility of a gas in a liquid is directly proportional to the partial pressure of the gas above the liquid. Higher pressure, higher solubility.
• Henry's Law Formula: p = K_H * x, where p is partial pressure of the gas, K_H is Henry's Law constant, and x is the mole fraction of the gas in the solution.
• Henry's Law Constant (K_H): Varies with the nature of the gas and solvent, and temperature. Higher K_H indicates lower solubility of the gas at a given partial pressure.
• Nature of Gas: Gases that react chemically with the solvent (e.g., NH₃ in H₂O forming NH₄OH) or can form H-bonds are significantly more soluble than non-reacting gases (e.g., N₂, O₂).

Must-Know Formula / Reaction

Henry's Law: p = K_H * x

• p: Partial pressure of the gas (atm or bar)
• K_H: Henry's Law constant (atm or bar/mole fraction)
• x: Mole fraction of the gas in the solution (dimensionless)

Common Mistakes

• Students often confuse the effect of temperature on gas solubility (decreases) with solid solubility (usually increases).
• Don't confuse a high K_H value with high solubility; remember, K_H is inversely related to solubility at a given pressure.
• Assuming Henry's Law is universally applicable; it works best for dilute solutions and low pressures, and for gases that do not react with the solvent.

Rapid Revision

Gas solubility decreases with temperature and increases with pressure (Henry's Law, p=K_H*x). Higher K_H means lower solubility. Remember reactive gases like NH₃ are exceptions to ideal Henry's Law behavior.