Calculate vapor pressure using the Antoine, Clausius-Clapeyron, and Raoult equations. Convert between units, estimate boiling points, and analyze solution vapor pressures.
Vapor pressure is the pressure exerted by a vapor in thermodynamic equilibrium with its liquid (or solid) phase at a given temperature. It is a fundamental physical property that governs boiling, evaporation, distillation, and the behavior of volatile substances in mixtures.
The Antoine equation is the most widely used empirical correlation for vapor pressure as a function of temperature: log₁₀(P) = A − B / (C + T). For thermodynamic derivations, the Clausius-Clapeyron equation relates vapor pressure to enthalpy of vaporization: ln(P₂/P₁) = −ΔHvap/R × (1/T₂ − 1/T₁).
This calculator supports both equations with built-in Antoine parameters for 30+ common substances, estimates boiling points at non-standard pressures, computes vapor pressures of ideal mixtures via Raoult's Law, and converts between mmHg, kPa, atm, bar, and psi.
For best results, combine calculator output with direct observation and periodic check-ins with a veterinarian or qualified advisor. Small adjustments made early usually improve comfort, safety, and long-term outcomes more than large corrective changes made later.
Vapor pressure calculations are central to chemical engineering (distillation design), environmental science (VOC evaporation), pharmaceutical stability studies, weather prediction (humidity), and industrial safety (flash point estimation). Consistent pressure modeling improves process planning and reduces errors when translating formulas between different unit systems and mixed regulatory documentation standards during design, reporting, and routine operations.
Antoine: log₁₀(P/mmHg) = A − B / (C + T/°C). Clausius-Clapeyron: ln(P₂/P₁) = −ΔHvap/R × (1/T₂ − 1/T₁). Raoult's Law: P_total = Σ xᵢ × P°ᵢ, where xᵢ is mole fraction and P°ᵢ is pure-component vapor pressure.
Result: 760.0 mmHg (101.33 kPa)
Using Antoine parameters for water (A=8.07131, B=1730.63, C=233.426): log₁₀(P) = 8.07131 − 1730.63/(233.426+100) = 2.881, P = 760.0 mmHg = 1 atm — confirming the normal boiling point.
The Antoine equation is a semi-empirical modification of the Clausius-Clapeyron equation. The three parameters (A, B, C) are fitted to experimental data and are valid only within a specified temperature range. The NIST WebBook is the most authoritative source for Antoine parameters.
Different sources may use different forms: some use log₁₀ with T in °C, others use ln with T in K. Always verify the convention before using published parameters.
For ideal mixtures, Raoult's Law connects vapor and liquid compositions through the relative volatility α = P°₁/P°₂. Distillation separations rely on α > 1 to enrich the more volatile component in the vapor phase. The larger α, the easier the separation.
Vapor pressure determines how quickly solvents evaporate, contributing to VOC emissions. OSHA uses vapor pressure to classify chemicals for workplace exposure limits. High-vapor-pressure substances (acetone, gasoline) require proper ventilation and ignition source control.
It is an empirical correlation of the form log₁₀(P) = A − B/(C+T) that accurately describes vapor pressure over a limited temperature range. Parameters A, B, C are substance-specific.
Use Clausius-Clapeyron when you have thermodynamic data (ΔHvap) and two reference P-T points but not Antoine parameters. It is thermodynamically grounded but assumes constant ΔHvap.
Raoult's Law states that the partial vapor pressure of each component in an ideal solution equals the product of its mole fraction and its pure-component vapor pressure. It applies to ideal or nearly ideal solutions.
At higher altitudes, atmospheric pressure decreases, lowering the boiling point. At 2000 m, water boils at about 93 °C. This calculator can find the boiling point at any pressure.
Common units include mmHg (torr), kPa, bar, atm, and psi. 1 atm = 760 mmHg = 101.325 kPa = 1.01325 bar = 14.696 psi.
Volatility depends on intermolecular forces. Weak London dispersion forces (e.g., diethyl ether) give high vapor pressure, while hydrogen bonding (e.g., water) gives lower vapor pressure at the same MW.