What does Raoult's law state?

a. The vapor pressure of a pure solvent is higher than that of a solution containing that solvent.

b. The vapor pressure of a pure solvent is lower than that of a solution containing that solvent.

c. The vapor pressure of a solute is the same as the vapor pressure of the solvent.

d. The vapor pressure of a solute is greater than that of a pure solvent.

is a law of thermodynamics established by French chemist François-Marie Raoult in 1887.[1] It states that the partial vapor pressure of each component of an ideal mixture of liquids is equal to the vapor pressure of the pure component multiplied by its mole fraction in the mixture.

Mathematically, Raoult's law for a single component in an ideal solution is stated as

{/displaystyle p_{i}=p_{i}^{/star }x_{i}},

where {/displaystyle p_{i}} is the partial vapor pressure of the component {/displaystyle i} in the gaseous mixture (above the solution), {/displaystyle p_{i}^{/star }} is the vapor pressure of the pure component {/displaystyle i}, and {/displaystyle x_{i}} is the mole fractionof the component {/displaystyle i} in the mixture (in the solution).[2]

Once the components in the solution have reached equilibrium, the total vapor pressure of the solution can be determined by combining Raoult's law with Dalton's law of partial pressures to give

{/displaystyle p=p_{/rm {A}}^{/star }x_{/rm {A}}+p_{/rm {B}}^{/star }x_{/rm {B}}+/cdots }.

If a non-volatile solute (zero vapor pressure, does not evaporate) is dissolved into a solvent to form an ideal solution, the vapor pressure of the final solution will be lower than that of the solvent. The decrease in vapor pressure is directly proportional to the mole fraction of solute in an ideal solution

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