Antoine Equation

The Antoine Equation calculator computes the apparent vapor pressure of pure substances based on temperature and coefficients for the substance.

INSTRUCTIONS: Choose units and enter the following:

• (T) Temperature
• (A) Coefficient A
• (B) Coefficient B
• (C) Coefficient C

Antoine Equation Pressure (p): The calculator returns the pressure in millimeters of mercury (mmHg).  However, this can be automatically converted to compatible units via the pull-down menu.

The Math / Science

The Antoine Equation is a mathematical expression used to describe the vapor pressure of a substance as a function of temperature. It is named after the French chemist Louis-Camille Antoine who proposed the equation. The general form of the Antoine Equation is:

log10​(P)=A−T+CB​

Where:

• P is the vapor pressure of the substance.
• T is the temperature in degrees Celsius.
• A, B, and C are constants specific to the substance.

The Antoine Equation is particularly useful in the field of thermodynamics and chemical engineering, especially when dealing with volatile substances. It is commonly employed for estimating vapor pressures, which is crucial in various applications such as:

• Process Design: In designing chemical processes involving distillation or evaporation, knowledge of vapor pressures at different temperatures is essential for determining optimal conditions.
• Safety: Understanding the vapor pressure of a substance helps in assessing its potential for evaporation and the associated safety concerns, especially in handling volatile chemicals.
• Material Compatibility: For selecting materials and designing equipment that will come into contact with substances having significant vapor pressures.
• Calibration of Instruments: In some cases, the Antoine Equation can be used to calibrate instruments that measure vapor pressures.

It's important to note that the accuracy of predictions using the Antoine Equation depends on the availability and accuracy of the constants AA, BB, and CC for the specific substance of interest. These constants are typically determined experimentally and may vary for different substances.

The form of the Antoine Equation used in this calculator is:

    p = 10^{(A - B/(C+T))}

where:

• p = vapor pressure
• T = temperature
• A, B, C are the Antoine Equation Coefficients

For the convenience of the user, unit conversions are supported.  Temperatures are converted to degree Celsius.  The coefficients are converted to millimeters of mercury (mmHg). 

Wikipedia provides the following Coefficient examples

Note from the math programmer:  The inconsistency of the units in the formula is maddening.  The wikipedia article indicates that the coefficients, presumably A, B and C, are in mmHg.  Algebraically, these do not cancel out.  For this reason, we take the article at face value, convert to degrees Celsius for the temperature and millimeters of mercury for the coefficients and then eliminate the units, treating the values as merely real numbers.  The ultimate value in the equation (p) is then espoused to be a pressure in the units of millimeters of mercury.  Any insight into this is very welcome, via the comments section, and changes will be made if this is in anyway incorrect.

The Water-Steam Equilibrium Vapor Calculator provides the constants A,B and C within the appropriate temperature ranges of the water vapor.

References

• Wikipedia - en.wikipedia.org/wiki/Antoine_equation

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