Margules function

A Margules function is a function added to the Raoult's law description of a liquid solution to account for deviations from ideality.

The amended Raoult's law description of the vapor pressure above the solution becomes:

P₁=P*₁x₁f_M,1

P₂=P*₂x₂f_M,2

The Margules function has the general form:

f_M,1 = exp(αx₂²+βx₂³+γx₂³+δx₂⁴+...)

The function always contains the opposite mole fraction x₂ (= 1-x₁ for a binary system). The numbers of Margules parameters α, β, γ, δ, .. varies. The larger the deviations from ideality the more parameters are required.

The Gibbs-Duhem relation can be used to fix the Margules function for the second component once the first has been chosen.

The case where only one parameter α is needed is known as the regular solution model.