🌡️

Vapor Pressure Calculator

Antoine Equation • NIST-Verified Constants

Advertisement
Vapor Pressure Calculator
Calculate component vapor pressures using the Antoine equation for phase equilibrium predictions. Essential for flash calculations, separator design, RVP estimation, and storage tank specifications.

Compound Selection

Temperature

°F

Antoine Constants

Select a compound to see Antoine constants.

Constants are verified against NIST Chemistry WebBook.

📚 Learn the Theory

Understand vapor pressure principles, Antoine equation, VLE calculations, and engineering applications

Read Engineering Guide →
📐 Engineering Note

Vapor pressure is the pressure exerted by a vapor in equilibrium with its liquid at a given temperature. It's fundamental to VLE calculations, distillation design, and safety relief sizing. At the normal boiling point, vapor pressure equals 1 atm (760 mmHg).

Formula

log₁₀(P) = A − B/(C + T)
P = Vapor pressure (mmHg)
T = Temperature (°C)
A, B, C = Compound-specific constants
💡 Pro Tip

At the normal boiling point, P = 760 mmHg (1 atm). Use this to verify calculations.

Engineering Notes

  • Accuracy: ±1-3% within valid temperature range. Extrapolation beyond range significantly decreases accuracy.
  • Mixtures: For multicomponent systems, use Raoult's Law: Ptotal = Σ(xi × Pi°)
  • RVP: Reid Vapor Pressure is measured at 100°F (37.8°C) per ASTM D323.
  • Critical applications: Verify with EOS models (Peng-Robinson, SRK) for final design.
  • Storage tanks: API 2000 requires vapor pressure for vent sizing.

Quick Reference: Normal Boiling Points

Compound NBP (°F) NBP (°C) Typical Use
Propane-44-42LPG, refrigerant R-290
n-Butane31-0.5LPG, aerosol propellant
n-Pentane9736Gasoline blending, blowing agent
n-Hexane15669Extraction solvent
n-Heptane20998Octane rating reference (0)
n-Octane258126Gasoline component
Methanol14965Hydrate inhibitor, fuel
Ethanol17378Fuel additive, solvent
Water212100Process steam
Advertisement

Standards & References

  • NIST Chemistry WebBook
    Primary source for Antoine constants
  • Yaws' Handbook
    Vapor Pressure: Antoine Coefficients
  • API Technical Data Book
    Petroleum Refining Properties
  • Perry's Chemical Engineers' Handbook
    8th Edition, Section 2
Advertisement