Raoult's Law Calculator
Compute partial and total vapor pressures of an ideal binary mixture from component moles and pure-component vapor pressures.
xₐ
0.6667
x_b
0.3333
Total vapor pressure
120 mmHg
Partial pressure A
53.3333 mmHg
Partial pressure B
66.6667 mmHg
How to Use This Calculator
Enter moles of each component
Use moles to determine mole fractions. Convert from mass if needed by dividing by molar mass.
Provide pure vapor pressures
Look up the vapor pressures of each component at the temperature of interest.
Review partial pressures
Raoult’s law multiplies mole fraction by pure vapor pressure to obtain partial pressures.
Sum to get total pressure
Total vapor pressure is the sum of component partial pressures in an ideal solution.
Formula
Pᵢ = xᵢ Pᵢ°
P_total = Σ Pᵢ
xᵢ is the mole fraction of component i, Pᵢ° is the vapor pressure of the pure component. Ideal solutions obey Raoult’s law across the composition range.
Example
For x_A = 0.4, P_A° = 120 mmHg, and P_B° = 300 mmHg, P_total = 0.4×120 + 0.6×300 = 228 mmHg.
Full Description
Raoult's law predicts vapor pressures for ideal liquid mixtures where intermolecular interactions between unlike molecules match those between like molecules.
The calculator helps chemists and engineers estimate total pressures, boiling points, or composition of vapor above a binary mixture by combining mole fractions with pure-component vapor pressures.
Frequently Asked Questions
When does Raoult's law apply?
It applies to ideal solutions. Deviations occur when molecular interactions differ significantly between components.
Can I input mole fractions directly?
You can convert mole fractions to moles by choosing a convenient basis (e.g., total moles = 1).
How do I handle temperature changes?
Update the pure vapor pressures to the temperature of interest using Antoine equations or reference tables.
What about nonvolatile solutes?
If component B is nonvolatile, set its vapor pressure to zero. The calculator then returns the solvent vapor pressure depression.
Does this compute boiling points?
No, but once you have total vapor pressure you can compare with ambient pressure to estimate boiling conditions.