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Thermodynamics — Vapor-Phase Association

Carboxylic-acid dimerization in the vapor phase (acetic acid and relatives) tracked via the Nagy chemical-theory equilibrium — the dimer/monomer split shifts the effective vapor enthalpy and density away from what an ideal-gas assumption would give.

thermodynamicsassociationdimerization
Concept

Carboxylic acids (acetic acid and relatives) hydrogen-bond into dimers in the vapor phase: 2A ⇌ A₂. An ideal-gas gamma-phi model gets the apparent vapor enthalpy and density wrong for these systems because the "vapor" is really a monomer/dimer equilibrium mixture with fewer effective moles than ideal gas predicts.

The math
Show the governing equations
K(T)=exp⁡ ⁣(−ΔHdim−T ΔSdimRT)K(T) = \exp\!\left(-\frac{\Delta H_{dim} - T\,\Delta S_{dim}}{RT}\right)
ΔHdim=−15.4 kcal/mol,ΔSdim=−36.6 cal/mol⋅K\Delta H_{dim} = -15.4\ \text{kcal/mol}, \quad \Delta S_{dim} = -36.6\ \text{cal/mol·K}
Cited, not estimated — from Nagy et al., Molecules 2020, 25(9), 2150 (NMR + quantum-chemical fit to 25-100 °C data).
Execution

Applies automatically wherever has_association(component) is true for the flowsheet's components (currently: acetic acid). No flowsheet configuration needed — the correction is folded into the vapor enthalpy calculation transparently.