Raoult’s Law

Raoult’s Law is a fundamental principle in thermodynamics that describes the vapour pressure of an ideal solution. It states that the partial pressure of each volatile component in an ideal mixture is directly proportional to the mole fraction of that component in the liquid phase and its pure component vapour pressure at the same temperature. Mathematically, Raoult’s Law is expressed as:

Symbol	Description	Unit
	Mole fraction of component in the liquid phase
	Vapour pressure of component  at the system temperature
	Partial pressure of component

Limitations

Raoult’s Law is most accurate for ideal solutions. Deviations occur when the solution is non-ideal, particularly in cases involving:

• Strong intermolecular interactions (e.g., hydrogen bonding).
• Significant differences in molecular size and shape.
• High solute concentrations.

In non-ideal solutions, activity coefficients are introduced to correct for these deviations, leading to a modified form of Raoult’s Law:

Where  is the activity coefficient of component , which accounts for non-ideal behaviour.