Raoult’s Law Calculator
A benzene–toluene liquid with 40 mol % benzene at 90 °C boils at 86.96 kPa, giving a vapour with 62.6 % benzene.
Benzene at 90 °C: 136.1 kPa.
Toluene at 90 °C: 54.2 kPa.
86.96 kPa
Full answer, then cut to fewer decimals (not rounded):
- 86.96 kPa
- 86.9 kPa
- Vapour mole fraction y₁
- 0.6260349586
- y₂
- 0.3739650414
- Relative volatility α = P₁ˢᵃᵗ/P₂ˢᵃᵗ
- 2.511070111
Step-by-step solution
- P = x₁P₁ˢᵃᵗ + x₂P₂ˢᵃᵗ = 0.4 × 136.1 + 0.6 × 54.2 = 86.96 kPa
- y₁ = x₁P₁ˢᵃᵗ/P = 0.6260349586
Raoult’s Law Formula
P = x₁P₁ˢᵃᵗ + x₂P₂ˢᵃᵗ, y₁ = x₁P₁ˢᵃᵗ/P
dew point: 1/P = y₁/P₁ˢᵃᵗ + y₂/P₂ˢᵃᵗ; α = P₁ˢᵃᵗ/P₂ˢᵃᵗ
Worked Example
A benzene–toluene liquid with 40 % benzene at 90 °C:
- P = x₁P₁ˢᵃᵗ + x₂P₂ˢᵃᵗ = 0.4 × 136.1 + 0.6 × 54.2 = 86.96 kPa
- y₁ = x₁P₁ˢᵃᵗ/P = 0.6260349586
y₂: 0.3739650414 · Relative volatility α = P₁ˢᵃᵗ/P₂ˢᵃᵗ: 2.511070111
GATE tip
Get the vapour pressures at the given temperature first, from the Antoine equation if the question gives its constants.
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Frequently asked questions
When does Raoult’s law apply?
For ideal liquid mixtures of similar molecules (benzene–toluene, hexane–heptane) at low pressure; otherwise add activity coefficients.
How is relative volatility used?
For constant α, y = αx/(1 + (α − 1)x), the equilibrium curve in McCabe–Thiele and Fenske calculations.
Sources
- The International System of Units (SI), 9th edition (SI Brochure), Bureau International des Poids et Mesures .
Last reviewed: . Factors are stored exactly and computed with 50-digit decimal arithmetic. See how we verify conversion factors.
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APA
Scientific Converters. (2026, October 15). Raoult’s Law Calculator. Retrieved October 29, 2026, from https://scientificconverters.com/calculators/raoults-law-calculator/
IEEE
Scientific Converters, "Raoult’s Law Calculator," scientificconverters.com. Accessed: Oct. 29, 2026. [Online]. Available: https://scientificconverters.com/calculators/raoults-law-calculator/