Raoult’s law

Raoult’s law was named after François-Marie Raoult, a French chemist who discovered during an experiment that when compounds were mixed in a solution, the solution’s vapour pressure reduced at the same time. Raoult’s law, commonly known as the law of thermodynamics, was created in the year 1887.

Roult’s Law

Raoults law states the partial vapour pressure of a solvent in a solution (or mixture) is equal to or identical to the vapour pressure of the pure solvent multiplied by its mole fraction in the solution, according to  Raoult’s law.

Psolution = Χsolvent*P0solvent

Where, 

• Psolution = vapour pressure of the solutions

• Χsolvent  = mole fraction of the solvents

• P0solvent = vapour pressure of the pure solvents

• Importance of Raoults law

Raoults Law and its Relationship with different Laws

Roult’s law resembles the ideal gas law in many ways. Raoult’s law is the only exception  that it applies only  on solutions. As we have  read about the ideal gas law, we know that it assumes ideal gas behaviour in which intermolecular interactions between dissimilar molecules are zero or non-existent. Raoult’s law, on the other hand, assume that intermolecular forces between different molecules and comparable molecules are equal.

Non-ideal solutions can also be subjected to Raoult’s law. This is accomplished, however, by taking into account a number of elements, including the interactions between molecules of various substances.

Working Principle of Roult’s law

Colligative qualities is a notion or a process. If we look at the reviews, we can see that more solute will fill the spaces between the solvent particles to take up space while also introducing a solute with a lower vapour pressure. As a result, vapour pressure is reduced since less solvent is able to break loose and enter the gas phase, leaving more solvent on the surface. Raoult’s Principle begins with a simple visual method and advances to a more extensive entropy-based approach. Let’s take a quick look at the approach presented below.

• The number of particles adhering to the surface is the same as in an equilibrium, and the number of particles breaking away from the surface is the same. Remember that saturated vapour pressure is what you get when a liquid is sealed in a container.

• A specific proportion of solvent molecules will have enough energy to escape from the surface (e.g., 1 in 1000 or 1 in a million). The ability of molecules will not be affected by vapour adhering to the surface again. The vapour may stick to a solvent molecule if it comes into touch with a region of the interface that is covered by solutes. If there is no visible attraction between the solvent and the solute, you would not have a solution in the first place.

Limitations of Raoults Law

Raoult’s law does have several limits which are as follows-:

• Ideal solutions are well described by Raoult’s law. Ideal solutions, on the other hand, are hard to come by and even more unusual. Chemically, different chemical components must be chemically equivalent.

• These types of solutions tend to diverge from the law since many of the liquids in the mixture do not have the same uniformity in terms of attractive forces.

• Either a negative or a positive deviation exists. When the vapour pressure is lower than expected by Raoult’s law, the negative deviation occurs. A mixture of chloroform and acetone, or a solution of water and hydrochloric acid, is an example of negative deviation.

• Positive deviation, on the other hand, occurs when the cohesion between comparable molecules is larger than or equal to the adhesion between unlike or dissimilar molecules. Both of the mixture’s components can easily elude the solution. Mixtures of benzene and methanol, or ethanol and chloroform, are examples of positive deviation

Conclusion

So we conclude from above that the partial vapour pressure of a solvent in a solution (or mixture) is equal to or identical to the vapour pressure of the pure solvent multiplied by its mole fraction in the solution, according to Raoult’s law. The Raoult law (Raoult, 1887) for optimal solutions is a similar topic. It proves that the vapour pressure of an ideal solution is directly proportional to the vapour pressure of each chemical component and the mole fraction of the components present.