However, we show on Fig. II-4 that the partial pressure of H2O, pW, approaches the dotted line of the figure, the hypothetical vapor pressure of Raoult`s law, as xTBA → 0. The other component, TBA, is so diluted that interactions with TBA do not affect H2O much, and TBA molecules only act as diluents for H2O. Thus, the partial pressure of H2O, pW, in this range is approximated as, Thus, if the solvent and dissolved molecules are of different sizes, the mole fractions must be replaced by the volume fractions. We note that Eq. (16.17)1 is the most general expression and includes the equation For example, the chloroform (CHCl3) and acetone (CH3COCH3) system has a negative deviation from Raoult`s law, indicating an attractive interaction between the two components, which have been described as a hydrogen bond.  The HCl water system has a negative deviation large enough to form a minimum in the vapour pressure curve called azeotrope (negative), which corresponds to a mixture that evaporates without changing composition.  When these two components are mixed, the reaction is exothermic because intermolecular ion-dipole attraction forces are formed between the resulting ions (H3O+ and Cl–) and polar water molecules, so that ΔHmix is negative. French chemist François-Marie Raoult discovered that when substances were mixed in a solution, the vapor pressure of the solution decreased simultaneously during an experiment in 1877.
Raoult proposed a principle known as Raoult`s rules to describe this phenomenon. Raoul`s law is known as one of the thermodynamic principles. It is a law that determines the boiling and freezing of an ideal or ideal solution. and with respect to the molar ratio of the solute to that of the pure solvent is pressed. To escape from the surface (e.g. 1 in 1000 or 1 in a million), a certain ratio of solvent molecules has enough energy. You will reduce the number of people who can run away at any given time if you reduce the solvent molecules to the surface. The vapor rising to the surface makes no difference in the capacity of the molecules.
When the vapor comes into contact with such a part of the interface covered by the solutes, it can adhere to a solvent molecule. Otherwise, you would have no solution if there was no obvious attraction between the solvent and the solute. Raoul`s law is expressed by the formula:Psolution = ΧsolventP0solvent where Psolution is the vapour pressure of the solutionΧsolvent is Mole fraction of the solventP0solvent is the vapour pressure of the pure solventIf more than one solute is added to the solution, the component of each solvent is added to the total pressure. The notation used in the molecular interpretation of Raoult and Henry`s laws with respect to interactions between particles, the solvent is called type A particles and the solute is called type B particles. FIGURE 14.9. Deviations from Raoult`s law. The black lines represent the ideal, Raoult`s law, behavior. The colored lines show deviations from the ideal behavior. The degree of deviation and, consequently, the shapes of the vapour pressure curves of the actual solution can vary considerably. Methyl alcohol (CH3OH) and water form a solution that deviates positively from Raoult`s law.
Nitric acid (HNO3) and aqueous solutions deviate negatively. Importance of Raoult`s Law for the Removal of Volatile ComponentsRaoult`s Law: PA=PA=Partial pressure of A of the solutionPA=PA0×NAPA0=pure vapour pressure pressure ANA=mol pressure fraction AVapor is essentially the tendency of molecules of A to escape from the solution into the vapor. Therefore, vapour particles A and B exert partial pressure that contributes to the total pressure on the solution. In this lesson, we will delve deeper into Raoult`s law and understand the principle behind the law, as well as its application and limitations. Ethylene bromide propylene bromide at 85°C (J. Z. von Zawidzki, Z phys. Chem. 35, 129 (1900)). Raoul`s law is also very similar to the ideal gas law.
The only exception to Raoult`s law is that it applies to solutions.