Ideal Dilute Solution Laws: Raoult's & Henry's

Understanding the behavior of components in an ideal dilute solution is key to applying the correct laws.

Raoult's Law Applicability

Raoult's law states that the partial vapor pressure of a solvent in an ideal solution is directly proportional to its mole fraction. The formula is:

$ P_{solvent} = x_{solvent} P_{solvent}^0 $

where \( P_{solvent} \) is the partial vapor pressure of the solvent, \( x_{solvent} \) is the mole fraction of the solvent, and \( P_{solvent}^0 \) is the vapor pressure of the pure solvent. This law accurately describes the solvent's behavior in an ideal solution, especially when the solvent constitutes the major component.

Henry's Law Applicability

Henry's law states that the partial pressure of a volatile solute is directly proportional to its mole fraction in a dilute solution. The formula is:

$ P_{solute} = K_H x_{solute} $

where \( P_{solute} \) is the partial pressure of the solute and \( K_H \) is Henry's constant. This law is applicable for the solute in dilute solutions where the solute concentration is low.

Behavior in Ideal Dilute Solutions

In an ideal dilute solution:

• The solvent behaves ideally and obeys Raoult's law.
• The solute, being present in low concentration, behaves ideally and obeys Henry's law.

Therefore, the statement that accurately describes an ideal dilute solution is that the solute obeys Henry's law and the solvent obeys Raoult's law.