Vapor Pressure Calculator

Calculate pure component saturation vapor pressure (Psat) using Antoine Equation and inverse boiling point solver. Interactive P-T diagram, NIST-validated coefficients for distillation, HVAC, meteorology and process design.

Valid range depends on substance
? Water boiling point (100°C → 101.325 kPa)
? Ethanol boiling point (78.37°C → 101.3 kPa)
? Acetone vapor pressure @20°C
✏️ Custom demo: Water coefficients
Privacy & Accuracy: All calculations are performed locally. Antoine coefficients from NIST and DDB databases. No data upload.

Antoine Equation: Core Correlation in Industrial Thermodynamics

The Antoine equation is a semi-empirical model describing the relationship between saturation vapor pressure and temperature for pure components. Widely used in process simulation and distillation design. Standard form:

log₁₀(Psat/mmHg) = A – B / (C + T/°C)

This calculator uses NIST and DIPPR-recommended coefficients. For water in the range 1–100°C error is below 0.2%. It also supports Clausius-Clapeyron theory background: ln(P) = -ΔHvap/RT + constant; Antoine enhances wide-range fitting.

Engineering Applications

  • Distillation & Flash: Determine condenser pressure and bubble point temperatures.
  • HVAC & Meteorology: Compute relative humidity and dew point from water vapor pressure.
  • Vacuum Distillation: Rapidly predict boiling points at reduced pressures to avoid thermal degradation.
Case Study: Ethanol Vacuum Distillation – Energy Optimization

An engineer needs to recover ethanol at an absolute pressure of 300 mmHg. Select "Ethanol", click "Boiling point @ given P", input 300 mmHg (or convert to desired unit). The solver returns boiling point ≈ 64.5°C, significantly lower than the normal boiling point of 78.4°C. This reduces energy consumption and prevents thermal degradation. Built-in Antoine coefficients A=8.20417, B=1642.89, C=230.300 match NIST data.

Reference Coefficients & Validation Table

Substance Antoine Constants (A, B, C) Temp. Range °C vs NIST error
Water 8.07131, 1730.63, 233.426 1–100 ±0.2%
Ethanol 8.20417, 1642.89, 230.300 0–100 ±0.3%
Acetone 7.02447, 1161.0, 224.0 -20–80 ±0.5%
Toluene 6.95805, 1346.773, 219.693 20–150 ±0.4%

References: NIST Chemistry WebBook, SRD 69; Poling et al. "Properties of Gases and Liquids" 5th ed.

FAQs & Technical Limitations

It is recommended to stay within the specified temperature range for each substance. Beyond that, deviations increase. Near-critical conditions require equations of state (PR, SRK).

This tool is for pure components only. For mixtures, use activity coefficient models (Wilson, NRTL) or Raoult's law.

Yes, the classic Antoine form outputs mmHg. When entering custom coefficients, ensure consistency; the tool automatically converts to your selected display unit.
This tool is validated against IAPWS-95 steam tables and ethanol vapor pressure experimental data. Coefficient library is regularly updated.