Vapor Pressure & Clausius-Clapeyron
Antoine-equation vapor pressure for common solvents, plus the Clausius-Clapeyron relation to find the enthalpy of vaporization or the vapor pressure at a second temperature.
How to use this tool
Find how readily a solvent evaporates at a given temperature, or how its vapor pressure changes as the temperature moves. Pick the mode that matches what you know, fill the boxes, and read the answer.
What to enter
- Mode: Vapor pressure (Antoine) for a named solvent at a temperature; Clausius-Clapeyron → ΔHvap to get the enthalpy of vaporization from two pressure–temperature points; or Clausius-Clapeyron → P₂ to predict a pressure at a new temperature.
- Antoine mode: a Solvent from the list and a Temperature in °C.
- → ΔHvap mode: two points, P₁, T₁ and P₂, T₂. Pressures can be in any unit as long as both match; temperatures in kelvin.
- → P₂ mode: one point P₁, T₁, the enthalpy of vaporization ΔHvap in J/mol, and the target temperature T₂ in K.
Reading the result
Antoine mode gives the vapor pressure in mmHg, kPa and atm, with a warning if your temperature is outside the solvent's fitted range. The Clausius-Clapeyron modes return either ΔHvap (kJ/mol) or the second pressure P₂ (in the same unit you used for P₁).
Worked example
In Antoine mode, pick water at 25 °C to get a vapor pressure of about 24 mmHg (≈ 3.2 kPa).
Inputs
Result
Antoine mode reports the same pressure in three units (mmHg, kPa, atm) and flags any temperature outside the solvent's fitted range as extrapolated. The Clausius-Clapeyron modes assume ΔHvap stays constant across the interval, so keep the two temperatures reasonably close for the best accuracy.
Methodology
Antoine: log₁₀(P[mmHg]) = A − B / (C + T[°C]), with solvent-specific A, B, C. Results outside the fit's validity window are flagged.
Clausius-Clapeyron: ln(P₂/P₁) = −(ΔHvap/R)·(1/T₂ − 1/T₁), with R = 8.314462 J·mol⁻¹·K⁻¹ and temperatures in kelvin. Given two pressure-temperature points it returns ΔHvap; given one point plus ΔHvap it returns P₂.
Sources
- Antoine constants from NIST / Lange's Handbook fits; validity windows in °C.
Known limits
- Clausius-Clapeyron assumes ΔHvap is constant over the temperature interval and ideal vapor.
- Antoine pressures are most accurate inside the stated range.