Raoult's Law vs. Henry's Law

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Sep 4, 2014
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When is one more accurate than the other? Raoult's Law vs. Henry's Law.

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The two laws are used for different purposes so you can’t really compare the accuracy between the two.

Raoult’s Law says the vapor pressure of a solvent above a solution is equal to the vapor pressure of the pure solvent at the same temperature scaled by the mole fraction of the solvent present: Raoult's Law

Henry’s Law says the solubility of a gas in a liquid is directly proportional to the partial pressure of the gas above the liquid: Henry's Law

Both laws can deal with gas-liquid equilibrium systems where the gas is the solute and the liquid is the solvent. Henry’s Law focuses on the behavior of the solute (i.e. the gas dissolved in liquid) at very dilute conditions, while Raoult’s Law focuses on the behavior of the solvent in a dilute solution. Dilute solutions are important because you want to minimize the intermolecular attractions that can cause the deviations from the laws’ predictions.

Both Henry’s Law and Raoult’s Law work in very ideal and dilute solutions. Raoult’s Law also works for non-gas solutes.

For more information, see: What are the key differences between Raoult’s Law and Henry’s Law

Just a heads up though. A lot of the details can be understood from taking a physical chemistry course but the details are beyond the scope of the MCAT. Just understand that Raoult’s Law and Henry’s Law are used for different purposes.