Raoult's Law Calculator

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Choose 'Binary ideal mixture' for two volatile components. Choose 'Nonvolatile solute' for a dissolved solid (e.g. sugar, salt) that does not contribute to vapor pressure.
All pure-component vapor pressures must be entered in the same unit.
Vapor pressure of pure component A at the temperature of interest. Benzene at 25 °C is about 96 mmHg.
mmHg
Fraction of the liquid-phase moles that are component A. Must be between 0 and 1. xB is automatically set to 1 minus xA.
Vapor pressure of pure component B at the same temperature. Toluene at 25 °C is about 29.1 mmHg.
mmHg
Total vapor pressure (Pₜₒₜₐℓ)
55.86mmHg

Sum of partial pressures of all volatile components (Dalton's Law).

Partial pressure of A (PA)38.4mmHg
Partial pressure of B (PB)17.46mmHg
Mole fraction of B in liquid (xB)0.6
Vapor mole fraction of A (yA)0.6874
Vapor mole fraction of B (yB)0.3126
PA (partial pressure A)38.4
PB (partial pressure B)17.46
Ptotal55.86

Total vapor pressure is 55.860 mmHg.

  • Component A has the higher partial pressure and therefore the greater contribution to total vapor pressure.
  • The vapor phase is enriched in component A relative to the liquid, as expected for the more volatile species.
  • This result assumes ideal behavior. Real mixtures may show positive or negative deviations from Raoult's Law when intermolecular forces between unlike molecules differ from those between like molecules.

Next stepTo model temperature-dependent vapor pressures, use the Antoine equation to find P° at a given temperature, then re-enter the values here.

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