What form of the Antoine equation does this tool use?

The tool uses the base-10 logarithm form: log₁₀(P*) = A − B/(C + T), where T is in Celsius and P* is in mmHg. This is the most common form found in Perry's Chemical Engineers' Handbook and NIST. If your source uses a natural-log or different units, convert the constants first.

When is Raoult's Law valid?

Raoult's Law is accurate for ideal or near-ideal mixtures — components with similar molecular structure and interactions (e.g., benzene-toluene, ethanol-propanol). It is less accurate for systems with strong hydrogen bonding or large polarity differences, which require activity coefficient models like NRTL or UNIQUAC.

Where do I find Antoine constants for a compound?

Reliable sources include the NIST WebBook (webbook.nist.gov), Perry's Chemical Engineers' Handbook, and Yaws' Handbook of Thermodynamic Properties. Always check the valid temperature range listed with each set of constants.

What is the difference between bubble point and dew point?

The bubble point is the temperature (or pressure) at which the first bubble of vapor forms from an all-liquid mixture. The dew point is the condition at which the first drop of liquid condenses from an all-vapor mixture. This tool calculates the bubble point pressure at a fixed temperature.

Why must mole fractions sum to 1?

For a binary mixture, x₁ + x₂ = 1 by definition. The tool enforces this by setting x₂ = 1 − x₁ automatically, so you only need to enter x₁.

Vapor-Liquid Equilibrium Calculator

Name: Vapor-Liquid Equilibrium Calculator
Availability: InStock
Author: Nham Vu

Enter Antoine constants and liquid-phase mole fractions for two components to calculate bubble point pressure and vapor compositions using Raoult's Law.

System Temperature

Component 1

Liquid mole fraction x₁ (0–1)

Component 2

Liquid mole fraction x₂ = 1 − x₁

P₁* (sat.)

—

mmHg

P₂* (sat.)

—

mmHg

Bubble Point P

—

mmHg

Vapor-Phase Mole Fractions

y₁ (Component 1) —

y₂ (Component 2) —

Full Calculation Summary

Parameter	Component 1	Component 2

Bubble Point Pressure — Unit Conversions

mmHg

—

kPa

—

atm

—

bar

—

Fill in Antoine constants and mole fraction, then click Calculate VLE.

Default values show benzene (1) — toluene (2) at 80°C.

Summary

Enter Antoine constants and liquid-phase mole fractions for two components to calculate bubble point pressure and vapor compositions using Raoult's Law.

How it works

Enter Antoine constants (A, B, C) for each component — these are tabulated for most common solvents.
Set the temperature in Celsius or Kelvin for the system.
Enter the liquid-phase mole fraction x₁ for component 1 (x₂ is calculated as 1 − x₁ automatically).
The tool computes each component's saturation pressure using the Antoine equation: log₁₀(P*) = A − B/(C+T).
Bubble point pressure P = x₁·P₁* + x₂·P₂* (Raoult's Law), and vapor fractions y = xᵢ·Pᵢ*/P.
Results update instantly as you change any input.

Use cases

Determine bubble point pressure for ethanol-water mixtures at distillation temperatures.
Design separation columns by knowing vapor compositions at given liquid compositions.
Validate textbook VLE problems for benzene-toluene or other ideal binary systems.
Estimate the vapor fraction of a solvent pair at a target operating pressure.
Support process simulation when a full software suite is unavailable.
Teach students Raoult's Law and the Antoine equation interactively.

Frequently Asked Questions

Last updated: 2026-06-18 · Reviewed by Nham Vu