Clausius-Clapeyron equation
The Clausius-Clapeyron equation relates the vapor pressure of a liquid at two different temperatures using the enthalpy of vaporization (ΔHvap):
ln(P₂/P₁) = −(ΔHvap/R) × (1/T₂ − 1/T₁)
For water: ΔHvap = 40,700 J/mol. For ethanol: ΔHvap ≈ 38,600 J/mol.