raoult's law is a law of thermodynamics established by french physicist franÃ§ois-marie raoult in 1882.. extract. 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 :p_i = p^{\star}_i x_i, where p_i is the partial vapor pressure of the component i in the gaseous mixture (above the solution), p_i^{\star} is the vapor pressure of the pure component i, and x_i is the mole fraction of the component i in the mixture (in the solution).a to z of thermodynamics by pierre perrot. isbn 0-19-856556-9 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 : p = p^{\star}_{\rm a} x_{\rm a} + p^{\star}_{\rm b} 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 pure solvent. == principle == thumb|vapor pressure of a binary solution that obeys raoult's law. the black line shows the total vapor pressure as a function of the mole fraction of component b, and the two green lines are the partial pressures of the two components. raoult's law is a phenomenological law that assumes ideal behavior based on the simple microscopic assumption that intermolecular forces between unlike molecules are equal to those between similar molecules: the conditions of an ideal solution. this is analogous to the ideal gas law, which is a limiting law valid when the interactive forces between molecules approach zero, for example as the concentration approaches zero. raoult's law is instead valid if the physical properties of the components are identical. the more similar the components are, the more their behavior approaches that described by raoult's law. for example, if the two components differ only in isotopic content, then raoult's law is essentially exact. comparing measured vapor pressures to predicted values from raoult's law provides information about the true relative strength of intermolecular forces. if the vapor pressure is less than predicted (a 
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