Boiling point at any pressure calculator
Calculator finds out boiling point under selected pressure using Clausius-Clapeyron's equation and reference data for given substance. For example, you can find out what is water's boiling point in high mountains, where the pressure is lower.

Beta version#

This online calculator is currently under heavy development. It may or it may NOT work correctly.
You CAN try to use it. You CAN even get the proper results.
However, please VERIFY all results on your own, as the level of completion of this item is NOT CONFIRMED.
Feel free to send any ideas and comments !

Input data#

Reference (known) boiling point°C
Pressure for reference boiling pointhPa
Enthalpy of vaporization of substancekJ/mol
Target pressurehPa


Boiling point under target pressure81.905732166°C

Some facts#

  • If we know the boiling point of the substance at some specific pressure (tables usually give the value under the so-called normal pressure i.e. 1013,25 hPa) and enthalpy of vaporization (molar heat of evaporation), then we can estimate the boiling point under another, selected pressure.
  • The relationship between pressure change and temperature change during evaporation (in general: phase transformation) is described by Clausius-Clapeyron equation. In the basic differential form, it looks as follows:
    dpdT=LTΔV\dfrac{dp}{dT} = \dfrac{L}{T\Delta V}
    • dpdT\dfrac{dp}{dT} - derivative of pressure after temperature under conditions of phase change equilibrium,
    • LL - heat of phase transformation,
    • TT - absolute temperature (in Kelvins),
    • ΔV\Delta V - change of volume accompanying the phase change.
  • In case of transformation of liquid into gas we can obtain the following relationship (after applying several approximations and integration):
    ln(p2p1)=ΔHR(1T21T1)ln\left(\dfrac{p_2}{p_1}\right) = -\dfrac{\Delta H}{R}\left(\dfrac{1}{T_2} - \dfrac{1}{T_1}\right)
    • p1p_1 - pressure at state 1,
    • p2p_2 - pressure at state 2,
    • T1T_1 - boiling point at state 1 (under pressure p1p_1),
    • T2T_2 - boiling point at state 2 (under pressure p2p_2),
    • RR - gas constant,
    • ΔH\Delta H - enthalpy of evaporation of substance.
  • Such an equation can be directly used to determine the boiling point under any pressure:
    T=[1TrefRln(ppref)ΔH]1T = \left[\dfrac{1}{T_{ref}} - R \dfrac{ln \left(\frac{p}{p_{ref}}\right)}{\Delta H}\right]^{-1}
    • TrefT_{ref} - known (reference) boiling point (under pressure prefp_{ref}),
    • prefp_{ref} - known (reference) pressure,
    • RR - gas constant,
    • ΔH\Delta H - enthalpy of vaporization of substance,
    • pp - the pressure for which we want to estimate the boiling point,
    • TT - the boiling point under selected pressure.

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