What Is Raoult’s Law?, Limitations, Application, Important Topics For JEE 2026

With JEE Main Session 2 running from April 2–8, 2026, this topic helps students revise an important Chemistry concept quickly. Understanding Raoult’s Law can improve accuracy in numerical and conceptual questions during the exam.

What Is Raoult’s Law? : Raoult’s Law, which discusses the relationship between ideal liquid mixture composition and vapour pressure, is an important concept in chemistry. The French scientist François-Marie Raoult first presented it in 1887. This law discusses the relationship between a part's pressure and its percentage in the mixture as a whole.

What is Raoult’s Law?

Some Basic Terms to Learn

• Solution: A solution is a homogenous mixture that contains two or more components.
• Solute: The substance that has been dissolved in the solvent is referred to as the solute.
• Solvents: A Solvent is a substance that dissolves the solute.
• Mole Fraction: The mole fraction is the ratio of a component's moles to the total moles in the solution.
• Vapour Pressure: Vapour pressure is the pressure exerted by a substance's vapour when in equilibrium with its liquid or solid form.
• Partial vapour pressure: When multiple liquids are combined, each adds to the total pressure exerted by the vapour above the combination. This contribution from each liquid is known as the partial vapour pressure.
• Mole fraction : The number of moles of a component divided by the total number of moles in the mixture. It is a dimensionless value between 0 and 1.

Importance of Raoult’s law

1. All solids and liquids display vapour pressure, which is solely dependent on the kind of liquid and temperature.
2. Suppose for a moment that we are filling this container with liquid B (solute). As a consequence, on the solution's surface, B particles will take up the space between A particles.
3. A portion of the molecules on the surface of any given liquid will have enough energy to escape into the vapour phase.
4. Now that there are fewer A particles on the surface, there will be less A vapor particles in the vapour phase. As a consequence, A's vapour pressure will decrease.
5. In comparison to pure liquid B, there will be less B particles in the vapour phase if we now assume that B is also volatile.
6. Raoult's law determines this new pressure, or partial pressure, of each (A and B), which is dependent upon the concentration of each component in the liquid phase.

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Relationship of Raoult’s Law With Other Laws

Similarity to Ideal Gas Law:

• Raoult's law is quite similar to the ideal gas law.
• But, it specifically applies to solutions, not gases.

Exception to Ideal Gas Law:

• Ideal gas law assumes no intermolecular forces between dissimilar molecules.
• Raoult’s law assumes equal intermolecular forces between different and similar molecules in solutions.

Applicability to Non-Ideal Solutions:

• Raoult’s law is versatile and can be used for non-ideal solutions.
• In such cases, various factors need consideration, especially interactions between molecules of different substances.

Ideal System Derivation:

• A perfectly ideal system involves an ideal liquid and ideal vapour.
• Combining Raoult’s law and Dalton’s law in this scenario yields a valuable equation.

Limitation of Raoult’s Law

• Raoult’s law is useful for describing ideal solutions. However, perfect solutions are hard to find, and they are rare. Different chemical components have to be chemically similar equally.
• Since many of the liquids that are in the mixture do not have the same consistency in terms of pulling forces, these types of solutions tend to stray away from the law.

Application of Raoult’s Law