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Fugacity of a mixture

 

 

It states relationships between partial molar properties of different species in a mixture so that:

In a binary system, if you know  of one species, using Gibbs – Dühem equation the  of other species can be calculated.

 

From the definition of partial molar properties, the characteristics of a mixture are given by the contribution of each component related to the number of moles present of each compound

 

 

 

 

 

 

 

then

 

 

 

 

but

 

 

 

 

 

 

since the molar property is constant and the overall change is given only by a change in the number of moles.

 

 

 

Finally the Gibbs - Dühem equation is defined as

 

 

 

 

 

 

Gibbs - Dühem Equation

Lewis fugacity rule

and

Example of the calculation of fugacity and fugacity coefficient of a mixture using Lewis fugacity rule

This means that the fugacity coefficient of component i in the mixture can be considered equal to the pure fugacity coefficient. This is a great advantage for calculations. The key point of this assumption is that the contribution given by intermolecular forces does not significantly change the numerical value that is obtained.

 

Important! This is only valid if any of the following takes place:

  • There is ideal gas behaviour (either low pressure or high temperature)

  • Component A is in excess, therefore the molar fraction of B is very low

  • The mixture is formed by molecules of similar nature

     

     

     

     

     

     

     

     

     

 

Here you can study how the fugacity is calculated for a mixture using the software Thermosolver. (Click on the top-right arrows)

Or if you prefer on PDF format:

This presentation we have prepared for you will help you decide between the the different models you will have as an option when making a simulation

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