Approximate vapor-pressure relation
Vapor pressure changes with temperature through latent enthalpy.
Key knowledge
For liquid–vapor equilibrium with ideal dilute vapor, negligible liquid molar volume and approximately constant molar vaporization enthalpy ΔH_vap, ln(p₂/p₁) = −(ΔH_vap/R)(1/T₂ − 1/T₁).
Values and equations
ln(p₂/p₁) = −(ΔH_vap/R)(1/T₂ − 1/T₁)
- p₁, p₂
- Saturation pressures Pa
- T₁, T₂
- Absolute temperatures K
- ΔH_vap
- Molar vaporization enthalpy J mol⁻¹
- R
- Molar gas constant J mol⁻¹ K⁻¹
Conditions and scope
- Both pressures are saturation pressures of the same substance; T₁,T₂ > 0 and p₁,p₂ > 0.
- The approximation must be confined to a suitable temperature range away from the critical region.
Sources · 1
References
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Evidence and review
Module 5, page 2, equation 5.1: integrated Clausius–Clapeyron vapor-pressure relation.
2026-10-10 · Integrated constant-enthalpy vapor approximation only; general coexistence slopes and mixtures excluded.
Entry details
Permanent link to this entry ↗- Record identity
- physics-clausius-clapeyron
- Revision
- university-reference.1
- Structured reference record
- University reference · University core expansion