Vapor pressure at a new temperature from Clausius–Clapeyron, or water via Antoine.
| p2 | – |
Use this calculator when you know p at one T and ΔHvap and want p at another T, or when you just want water’s vapor pressure in mmHg between about 1 and 100 °C.
Clapeyron mode: ln(p₂/p₁) = −(ΔH/R)(1/T₂ − 1/T₁) with ΔH in J/mol. Temperatures may be entered in °C or °F; they are converted to kelvin. Water mode uses the Antoine equation; p1 and ΔH are unused and p₂ is mmHg. This is not a steam table.
Mode: Clausius–Clapeyron for a general liquid, or Antoine for water in mmHg.
p1 (Clapeyron): Known vapor pressure at T1, any unit you want back. Unused in water mode.
T1: Temperature of that known pressure, in °C or °F. Unused in water mode.
ΔHvap (J/mol): Enthalpy of vaporization in J/mol. 40650 is a typical textbook value for water. Unused in water mode.
T2: Temperature where you want p2, in °C or °F. For water, stay near 1–100 °C.
p2: Vapor pressure at T2, same unit as p1 in Clapeyron mode, mmHg in water mode.
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