Raoult's Law Calculator

Raoult's law gives the vapor pressure of an ideal solution.

How the Math Works

Raoult's Law calculates a solution's vapor pressure by multiplying the solvent's mole fraction (x_solvent) by its pure vapor pressure (P°_solvent). The mole fraction is determined by dividing the moles of solvent by the total moles in the solution, accounting for any dissolved solutes. This relationship shows that adding a solute lowers the vapor pressure proportionally to its concentration, as fewer solvent molecules escape into the vapor phase. The formula P = x_solvent × P°_solvent provides a straightforward way to quantify this effect using basic mole calculations.

Practical Applications

To apply this calculation, first measure or look up the pure solvent's vapor pressure at the given temperature. Then, determine the moles of solvent and solute in the solution to compute x_solvent. For example, if a solution contains 1 mole of water and 0.5 moles of sucrose, x_solvent = 1/(1+0.5) = 0.667. Multiply this by water's vapor pressure (e.g., 23.8 mmHg at 25°C) to find the solution's vapor pressure (15.87 mmHg). This is critical in labs for preparing solutions with specific boiling points or in industrial processes requiring precise evaporation control.

Day-to-Day Use

Raoult's Law helps explain everyday phenomena like why saltwater boils at a higher temperature than pure water or why perfumes evaporate slower when mixed with alcohol. It also plays a role in food preservation, where reducing a liquid's vapor pressure can extend shelf life by slowing spoilage-causing microbial growth. Additionally, understanding this principle aids in optimizing products like cleaning agents, where controlling evaporation rates ensures effectiveness while minimizing environmental impact through reduced volatile organic compound emissions.

Worked example

x 0.9, P° 3.17 kPa → 2.85 kPa.

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