Chemistry
Vapor Pressure Calculator
Use the Clausius-Clapeyron equation to move a known vapour pressure to a new temperature.
Your inputs
Change any value to update the result instantly.
Vapour pressure at T₂
42.5942 kPa
In mbar
425.942 mbar
In mmHg
319.483 mmHg
Ratio P₂/P₁
0.4204
Reading
Less volatile at the lower temperature
The integrated form assumes ΔH_vap stays constant between the two temperatures and that the vapour behaves ideally. Over a wide temperature span, use a fitted Antoine correlation instead.
What this calculator does
Moves a known vapour pressure to a new temperature with the integrated Clausius-Clapeyron equation.
What your result means
How much more or less volatile the liquid is at the new temperature.
Formula and working
ln(P₂/P₁) = −(ΔH_vap / R) × (1/T₂ − 1/T₁)
- 1
Collect the inputs
Known vapour pressure P₁ = 101.325 kPa; Temperature for P₁ = 373.15 K; New temperature T₂ = 350 K; Enthalpy of vaporisation = 40.65 kJ/mol
- 2
Apply the formula
ln(P₂/P₁) = −(ΔH_vap / R) × (1/T₂ − 1/T₁)
- 3
Result
Vapour pressure at T₂ = 42.5942 kPa
Frequently asked questions
Symbols and assumptions
- ΔH_vap
- Enthalpy of vaporisation
- R
- Gas constant
- P1, P2
- Vapour pressures
- T1, T2
- Temperatures
- • The enthalpy of vaporisation is constant between the two temperatures.
- • The vapour behaves ideally and its volume dwarfs the liquid volume.
Sources and review
Reviewed 2026-09-22 · Next review 2027-09-22
- • Over wide temperature spans a fitted Antoine correlation is more accurate.
Important limitation
This is an educational estimate based only on the values and formula shown. Verify current rates, rules, units, and professional standards before relying on the result. It is not personalized financial or investment advice.
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