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

Ideal solution

In chemistry, an ideal solution or ideal mixture is a solution with thermodynamic properties analogous to those of a mixture of ideal gases. The enthalpy of solution is zero as is the volume change on mixing; the closer to zero the enthalpy of solution is, the more "ideal" the behavior of the...

. See also Margules activity model

Margules activity model

-Introduction:Max Margules introduced in 1895 a simple thermodynamic model for the excess Gibbs free energy of a liquid mixture.After Lewis had introduced the concept of the activity coefficient, the model could be used to derive an expression for the activity coefficients \gamma_iof a compound i...

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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

Regular solution

In chemistry, a regular solution is a solution that diverges from the behavior of an ideal solution only moderately. Its entropy of mixing is equal to that of an ideal solution with the same composition, due to random mixing without strong specific interactions...

model.

External links

• http://wikis.lib.ncsu.edu/index.php/CH_431/Lecture_14#Margules_functions