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#

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This online calculator is currently under heavy development. It may or it may NOT work correctly.
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However, please VERIFY all results on your own, as the level of completion of this item is NOT CONFIRMED.
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Input data#

Reference (known) boiling point	°C
Pressure for reference boiling point	hPa
Enthalpy of vaporization of substance	kJ/mol
Substance
Target pressure	hPa

Results#

Boiling point under target pressure

81.905732166

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:

$\dfrac{dp}{dT} = \dfrac{L}{T\Delta V}$
where:
- $\dfrac{dp}{dT}$ - derivative of pressure after temperature under conditions of phase change equilibrium,
- $L$ - heat of phase transformation,
- $T$ - absolute temperature (in Kelvins),
- $\Delta V$ - 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):

$ln\left(\dfrac{p_2}{p_1}\right) = -\dfrac{\Delta H}{R}\left(\dfrac{1}{T_2} - \dfrac{1}{T_1}\right)$
where:
- $p_1$ - pressure at state 1,
- $p_2$ - pressure at state 2,
- $T_1$ - boiling point at state 1 (under pressure $p_1$ ),
- $T_2$ - boiling point at state 2 (under pressure $p_2$ ),
- $R$ - gas constant,
- $\Delta H$ - enthalpy of evaporation of substance.
Such an equation can be directly used to determine the boiling point under any pressure:

$T = \left[\dfrac{1}{T_{ref}} - R \dfrac{ln \left(\frac{p}{p_{ref}}\right)}{\Delta H}\right]^{-1}$
- $T_{ref}$ - known (reference) boiling point (under pressure $p_{ref}$ ),
- $p_{ref}$ - known (reference) pressure,
- $R$ - gas constant,
- $\Delta H$ - enthalpy of vaporization of substance,
- $p$ - the pressure for which we want to estimate the boiling point,
- $T$ - the boiling point under selected pressure.

Tags and links to this website#

Tags:

boiling_point_calculator · boiling_point_at_pressure · boiling_point_in_mountines

Tags to Polish version:

kalkulator_temperatury_wrzena · temperatura_wrzenia_pod_cisnieniem · temperatura_wrzenia_w_gorach

What tags this calculator has#

CALCULATOR · CHEMISTRY · PHYSICS · A -> Z (all)

Permalink#

This is permalink. Permalink is the link containing your input data. Just copy it and share your work with friends:

https://calculla.com/boiling_point_calculator?inBoilingPointReference=100&inPressureReference=1013.25&inEnthalpyOfVaporization=43&inPressureTarget=500&inSubstanceId=-1

Links to external sites (leaving Calculla?)#