Calculate the vapor pressure of an ideal solution using the mole fraction and vapor pressure of the pure solvent.
Solution Properties
Vapor Pressure Results
Enter mole fraction and pure vapor pressure
About this calculator
Overview
Raoult's Law describes how the vapor pressure of a solvent changes when a solute is added. It is the foundation for understanding colligative properties like boiling point elevation and freezing point depression.
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Pro Tips
Mole fraction (X) of the solvent is the ratio of solvent moles to total moles (solvent + solute).
Ideal solutions follow this law exactly. In reality, deviations occur if solute-solvent attraction differs from pure-solvent attraction.
Negative deviation (lower pressure than predicted) happens when solute and solvent attract each other strongly (e.g., acetone and chloroform).
Positive deviation (higher pressure than predicted) occurs when molecules 'dislike' each other and want to escape more easily.
Vapor pressure units (mmHg, kPa, atm) will be the same for both the pure solvent and the result.
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Fun Facts
"Ethylene glycol is used in car radiators because it follows Raoult's Law to lower the water's vapor pressure, which prevents both boiling in summer and freezing in winter."
"The 'smell' of the ocean is partly due to Raoult's Law; salts in the water affect the vapor pressure of organic compounds, changing how they evaporate into the air."
"High-purity ethanol (200 proof) cannot be made by simple distillation due to azeotropic behavior, which is a significant deviation from Raoult's Law."
"Marine birds and sea turtles have salt glands that concentrate salt, effectively using the principles of vapor pressure and osmosis to 'drink' seawater."
"Vacuum distillation uses the inverse of Raoult's principles to boil liquids at much lower temperatures, protecting heat-sensitive molecules like vitamins."
