Raoult’s Law Definition

Raoult’s law states that,

For a liquid solution having volatile components, the partial vapour pressure of a component is directly propotional to its mole fraction in the solution.

For example, consider a solution having two volatile components 1 and 2, then by Raoult’s law, partial pressure of 1 is written as,

p₁ = p₁⁰x₁ and p₂ = p₂⁰x₂

where,

• p₁ is Partial Pressure of Component 1
• p₂ is Partial Pressure of Component 2
• p₁⁰ is Vapour Pressure of Component 1 in Pure Form
• p₂⁰ is Vapour Pressure of Component 2 in pure form
• x₁ is Mole Fraction of Component 1 in Solution
• x₂ is Mole Fraction of Component 2 in Solution

Now, according to Dalton’s law of partial pressures which states the total vapour pressure of a solution is the sum of partial pressures of its constituents. Thus,

p_{Total =} p₁⁰x₁ + p₂⁰x₂

where,

• p_Total is Total Vapour Pressure of Solution

Thus, we can determine the total vapour pressure of a liquid solution using Raoult’s law and Dalton’s law of partial pressures.

Raoult’s Law in chemistry relates partial pressures of volatile liquid components to their mole fractions in a liquid solution. It states that the partial pressure of each component in the solution is directly proportional to its mole fraction. Thus, it helps us to calculate the total vapour pressure of the solution. Based on Raoult’s law, liquid solutions are classified as Ideal Solutions and Non-Ideal Solutions.

In this article, we will discuss the definition of Raoult’s law, ideal and non-ideal solutions, Raoult’s law for non-volatile solutes and some solved numerical problems based on Raoult’s law.