What Raoult’s Law describes
Raoult’s Law relates the vapor pressure of a solution to the vapor pressure of its pure solvent and the amount of solute dissolved in it. It applies best to ideal solutions where solute and solvent molecules interact similarly to how solvent molecules interact with each other.
The formula used
P(solution) = X(solvent) × P(pure solvent), where X(solvent) is the mole fraction of solvent, calculated as moles of solvent divided by total moles of solvent plus solute. Adding a non-volatile solute lowers the mole fraction of solvent, which lowers the overall vapor pressure; this vapor pressure lowering equals P(pure) minus P(solution), and is also equal to X(solute) × P(pure) for a single non-volatile solute.
- This calculator assumes the solute is non-volatile, so it contributes no vapor pressure of its own.
- Real (non-ideal) solutions can deviate from Raoult’s Law due to differing intermolecular forces.
Intended for general chemistry education and reference purposes.