Antoine Vapor Pressure Calculator
Calculate the vapor pressure of common liquids at any temperature using the Antoine equation.
Covers water, ethanol, methanol, acetone, benzene, toluene, and more.
The Antoine Equation The Antoine equation is an empirical formula for the vapor pressure of a liquid as a function of temperature: log₁₀(P) = A − B / (C + T) Where: P = vapor pressure (mmHg or bar, depending on constants), T = temperature (°C or K), A, B, C = Antoine constants specific to each substance. It was proposed by Charles Marie Antoine, a French engineer, in 1888 in France. The equation is widely used in distillation design, safety engineering, and chemical process simulation.
What Is Vapor Pressure? Vapor pressure is the pressure exerted by a liquid’s vapor when liquid and vapor are in equilibrium. Higher vapor pressure → substance evaporates more readily → lower boiling point. At the boiling point, vapor pressure equals atmospheric pressure (101,325 Pa = 760 mmHg = 1 atm). Temperature has an exponential effect on vapor pressure — the Antoine equation captures this well.
Clausius-Clapeyron Comparison The simpler Clausius-Clapeyron equation: d(ln P)/dT = ΔH_vap / (RT²) assumes constant heat of vaporization. The Antoine equation is empirically fitted and more accurate over a given temperature range. Both fail outside their fitted range — do not extrapolate far beyond the listed valid range.
Common Applications Distillation column design: vapor-liquid equilibrium (VLE) calculations require accurate vapor pressures. Safety: flash points, evaporation rates of chemicals in storage. Atmospheric chemistry: Henry’s Law constants, aerosol formation, cloud physics. HVAC and refrigeration: refrigerant pressure-temperature relationships.
Reading Boiling Point from Vapor Pressure Set P = 760 mmHg (1 atm) and solve for T: T = B / (A − log₁₀(760)) − C This gives the normal boiling point — the temperature at which the substance boils at sea level.
Raoult’s Law (Ideal Mixtures) For ideal liquid mixtures, each component’s partial pressure follows Raoult’s Law: P_i = x_i × P*_i where x_i = mole fraction, P*_i = pure component vapor pressure. Total pressure = sum of all partial pressures. Non-ideal mixtures require activity coefficients (Wilson, NRTL, UNIQUAC equations).
Pressure Units 1 atm = 760 mmHg = 101,325 Pa = 1.01325 bar = 14.696 psi. Vapor pressures are often quoted in mmHg (historical) or kPa (modern SI).