Raoults Law Calculator

mmHg
Water at 25°C: 23.8 mmHg.
mol
mol
Chemistry

Calculate the vapor pressure of a solution using Raoult's Law, and the boiling point elevation.

Formula

P_solution = χ_solvent × P°_solvent
  • Raoult's Law: partial vapor pressure of solvent = mole fraction × pure solvent vapor pressure.
  • Adding a non-volatile solute lowers the vapor pressure (colligative property).
  • Mole fraction χ = n_solvent / (n_solvent + n_solute).
  • Valid for ideal solutions (dilute, similar molecular interactions).

Water at 25°C with 1 mol solute in 5 mol water

Inputs
  • Vapor Pressure of Pure Solvent (P°): 23.8 mmHg
  • Moles of Solvent: 5 mol
  • Moles of Solute: 1 mol

χ = 5/6 = 0.833. P = 23.8 × 0.833 = 19.8 mmHg.

Frequently asked questions

What is Raoult's Law used for?
Calculating vapor pressure lowering, boiling point elevation, and freezing point depression of solutions.
When does Raoult's Law fail?
For non-ideal solutions with strong solute-solvent interactions or volatile solutes.