Antoine Equation Vapor Pressure Calculator
Our physical chemistry calculator computes antoine equation vapor pressure accurately. Enter measurements for results with formulas and error analysis.
Formula
log10(P) = A - B / (C + T)
P is the vapor pressure (typically in mmHg), T is the temperature (typically in degrees Celsius), and A, B, C are substance-specific empirical constants. The equation accurately describes the exponential relationship between vapor pressure and temperature over moderate ranges.
Worked Examples
Example 1: Water at 100 C
Problem: Calculate the vapor pressure of water at 100 C using Antoine constants A=8.07131, B=1730.63, C=233.426.
Solution: log10(P) = 8.07131 - 1730.63 / (233.426 + 100)\nlog10(P) = 8.07131 - 1730.63 / 333.426\nlog10(P) = 8.07131 - 5.18982\nlog10(P) = 2.88149\nP = 10^2.88149 = 760.96 mmHg
Result: P = 760.96 mmHg (approximately 1 atm, confirming boiling point)
Example 2: Ethanol at 78 C
Problem: Calculate ethanol vapor pressure at 78 C using A=8.20417, B=1642.89, C=230.300.
Solution: log10(P) = 8.20417 - 1642.89 / (230.300 + 78)\nlog10(P) = 8.20417 - 1642.89 / 308.300\nlog10(P) = 8.20417 - 5.32821\nlog10(P) = 2.87596\nP = 10^2.87596 = 751.22 mmHg
Result: P = 751.22 mmHg (near 760, confirming ~78 C boiling point)
Frequently Asked Questions
What is the Antoine equation?
The Antoine equation is a semi-empirical correlation that describes the relationship between vapor pressure and temperature for pure substances. The equation is log10(P) = A - B / (C + T), where P is the vapor pressure, T is the temperature, and A, B, and C are substance-specific constants determined from experimental data. It is one of the most widely used equations in chemical engineering for vapor pressure estimation due to its simplicity and reasonable accuracy over moderate temperature ranges. The equation was developed by French chemist Louis Charles Antoine in 1888.
What are Antoine constants and where do I find them?
Antoine constants (A, B, and C) are empirically determined parameters that are unique to each chemical substance and depend on the temperature range and pressure units used. They are tabulated in reference databases such as the NIST WebBook, the Yaws Handbook of Vapor Pressure, Perrys Chemical Engineers Handbook, and the DIPPR database. It is crucial to use constants that match your pressure units (typically mmHg or bar) and that are valid for your temperature range, as using constants outside their valid range can produce large errors in the calculated vapor pressure.
How accurate is the Antoine equation?
The Antoine equation is generally accurate to within 1-3% over its valid temperature range, which typically spans from about 10 C below the normal boiling point to the critical temperature. Its accuracy decreases significantly near the critical point and at very low temperatures far from the boiling point. For more accurate results over wider temperature ranges, extended Antoine equations with additional parameters or the Wagner equation are preferred. The three-parameter Antoine equation is favored in practice because it offers a good balance between accuracy and simplicity for engineering calculations.
What is vapor pressure and why does it matter?
Vapor pressure is the pressure exerted by a vapor in thermodynamic equilibrium with its liquid phase at a given temperature. It increases exponentially with temperature because more molecules have sufficient kinetic energy to escape the liquid surface. Vapor pressure is fundamental to many applications: it determines boiling points (a liquid boils when its vapor pressure equals atmospheric pressure), governs evaporation rates, is essential for designing distillation columns and evaporators, and is used in environmental science to predict volatility and atmospheric transport of chemicals.
How does the Antoine equation relate to the Clausius-Clapeyron equation?
The Clausius-Clapeyron equation provides the theoretical basis for the temperature dependence of vapor pressure: dln(P)/dT = delta_Hvap / (R * T^2), where delta_Hvap is the enthalpy of vaporization. Integrating this equation with the assumption of constant enthalpy gives ln(P) = -delta_Hvap/(RT) + constant, which is a two-parameter equation. The Antoine equation can be viewed as an improved empirical version that adds the C parameter to better fit experimental data, effectively accounting for the temperature dependence of delta_Hvap. When C = 0, the Antoine equation reduces to the Clausius-Clapeyron form.
Can I use Antoine Equation Vapor Pressure Calculator on a mobile device?
Yes. All calculators on NovaCalculator are fully responsive and work on smartphones, tablets, and desktops. The layout adapts automatically to your screen size.