Vapour pressure and boiling point
Antoine equation vapour pressure for 25 common process chemicals. Enter a temperature to get the vapour pressure, or a pressure to get the boiling point, with the Clausius–Clapeyron dT/dP slope.
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Liquid and gas properties for 543 chemicals — density, viscosity, conductivity, cp, vapour pressure, surface tension, Z factor and more — with print-ready reports, any units and visible formulas.
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How this calculator works
The Antoine equation relates the vapour pressure of a pure liquid to its temperature: log10(PmmHg) = A − B / (C + T°C). Each chemical has its own fitted constants A, B and C, published in the NIST Chemistry WebBook. This calculator covers 25 chemicals commonly found in process plants: water, alcohols, solvents, hydrocarbons, amines and a few others.
In Temperature → Pressure mode, enter a temperature and the calculator returns the vapour pressure in kPa, mmHg and psia. In Pressure → Boiling point mode, enter a system pressure and get the temperature at which the liquid boils. Both modes show the Clausius–Clapeyron slope dT/dP, which tells you how many degrees the boiling point shifts per kPa of pressure change — useful for understanding how column pressure affects tray temperatures.
Verification: water at 101.325 kPa (1 atm) gives a boiling point of 100.0 °C. Ethanol at 78.37 °C gives approximately 101.3 kPa. Acetone at 56.05 °C gives approximately 101.3 kPa.
Limits: the Antoine equation is empirical and accurate only within the fitted temperature range (shown for each chemical). Outside that range the result is an extrapolation and may be inaccurate, especially far from the fitted region or near the critical point. For mixtures, the vapour pressure is not additive — use Raoult’s law or an activity-coefficient model instead. References: NIST Chemistry WebBook; Reid, Prausnitz & Poling, The Properties of Gases and Liquids (5th ed.).