Henry's LawSolutionsNEET ChemistryNEET 2025Solubility of GasesGas Solubility
Henry's Law for NEET: Key Points, Tricks & MCQs
Solutions·2 min read·NEET 2026
What NEET Asks
Conceptual questions: Direct statement, factors affecting solubility of gases, applications in daily life and biology.
Numerical problems: Calculating partial pressure or mole fraction of a gas in solution.
Weightage: Moderate, often appears as part of a larger problem on solutions or directly as a single MCQ.
Key Points
Statement: Henry's Law states that the partial pressure of the gas ($P_A$) in the vapor phase is directly proportional to the mole fraction of the gas ($x_A$) in the solution.
Mathematical Form: $P_A = K_H \cdot x_A$, where $K_H$ is Henry's Law constant.
Solubility Relation: Higher $K_H$ at a given temperature implies lower solubility of the gas in the liquid.
Temperature Effect: The solubility of gases in liquids always decreases with increasing temperature (exothermic dissolution).
Applications: Carbonated beverages (CO$_2$ solubility), deep-sea diving (N$_2$ solubility and decompression sickness), high-altitude sickness (O$_2$ solubility in blood).
Limitations: Applicable for dilute solutions, low gas pressures, and gases that do not react chemically with the solvent or undergo dissociation/association.
Must-Know Formula / Reaction
$P_A = K_H \cdot x_A$
$P_A$: Partial pressure of the gas above the solution.
$K_H$: Henry's Law constant (units are same as pressure, e.g., atm, bar).
$x_A$: Mole fraction of the gas in the solution (dimensionless).
Common Mistakes
Students often confuse the direct or inverse proportionality between $K_H$ and solubility. Remember: higher $K_H$ = lower solubility.
Don't apply Henry's Law to gases that react chemically with the solvent (e.g., NH$_3$ or HCl in water) or when concentrations are high.
Forgetting to convert units of partial pressure and $K_H$ to be consistent before calculations.
Rapid Revision
Henry's Law ($P_A = K_H \cdot x_A$) quantifies gas solubility: partial pressure directly relates to mole fraction. High $K_H$ means low solubility. Remember its applications in drinks, diving, and altitude, and its limitations (dilute, non-reactive gases, low pressure).
Frequently Asked Questions
What is the main statement of Henry's Law?▾
Henry's Law states that the partial pressure of a gas in the vapor phase above a liquid is directly proportional to the mole fraction of the gas in the solution. This law describes the solubility of a gas in a liquid at a constant temperature.
How does Henry's Law constant ($K_H$) relate to gas solubility?▾
A higher value of Henry's Law constant ($K_H$) for a gas at a given temperature indicates lower solubility of that gas in the liquid. Conversely, a lower $K_H$ means higher solubility, as the gas dissolves more readily under the same partial pressure.
What are some practical applications of Henry's Law?▾
Henry's Law explains phenomena like the fizz in carbonated drinks (CO2 solubility increases with pressure). It's crucial in understanding decompression sickness for scuba divers (nitrogen solubility changes with depth) and respiratory problems at high altitudes (lower oxygen partial pressure means less dissolved oxygen in blood).
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