Activity Coefficient Model: UNIQUAC

The model is described in: Bruce E. Poling, John M. Prausnitz, John P. O'Connell, The Properties of Gases and Liquids, 5th ed., (New York: McGraw-Hill, 2001).

The following expressions define the terms leading to the equation for G^EX.

t₁₂ = exp{-u₁₂/(R ×T)} ; and t₂₁ = exp{-u₂₁/(R ×T)}; for the symmetric form, u₁₂ = u₂₁
t₁ = (x₁ ×q₁)/{x₁ ×q₁ + (1 - x₁)×q₂} and t₂ = {(1 - x₁)×q₂}/{x₁ ×q₁ + (1 - x₁)×q₂}
f₁ = (x₁ ×r₁)/{x₁ ×r₁ + (1 - x₁)×r₂} and f₂ = {(1 - x₁)×r₂}/{x₁ ×r₁ + (1 - x₁)×r₂}

G^EX/(R ×T) = -q₁ ×x₁ ×ln(t₁ + t₂ ×t₂₁) - q₂ ×x₂ ×ln(t₂ + t₁ ×t₁₂) + x₁ ×ln(f₁/x₁) + x₂ ×ln(f₂/x₂) + 5{q₁ ×x₁ ×ln(t₁/f₁) + q₂ ×x₂ ×ln(t₂/f₂)}

Details of the model implementation in TDE, including ThermoML-Equation representation are available. (See the ThermoML web site for details of this IUPAC communication standard.)