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Isis Hernandez

on 4 October 2013

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Transcript of dfsg

Activity, excess functions and Activity Coefficients
Student: Isis Hernández R.
Proffesor: Rigoberto Rios

Advanced Thermodynamics
The function Activity...
It´s auxiliary thermodynamic property
related to the Gibbs energy, applicable primarily to:
Liquid and Solid phases
Activity Coefficient...
These is a measure of the nonideality. Represent the deviations from the ideal behavior, and act as correction factors Raoult's law modificated.
Excess property...
It´s a deviation of mixture (real value) from ideal dilution behavior at same P, T and X.
tendency to escape
This functions are able to express the Gibbs free energy (and thus the conditions of phase equilibrium and chemical equilibrium) as a function of the thermodynamic variables of the gas.
Using for component of solution
Activity Coefficient
Van Laar
Without many different chemical components, except for the size of their molecules
Solution binary whose components are not very different in molecular size.
Applicable to systems partial miscibility. Strongly nonideal
By binary sistem
Gamero R. Termodinámica Avanzada. Termodínamica del equilibrio. Mezclas Líquidas. En línea: http://www.sarec-fiq.edu.ni/pmciq/che570/pdf/3g.pdf
Valid for simple solutions preferably non-polar
If constant of Van Laar A´ and B´ is equal, so...
The parameters have physical meaning:
Effective volume of the molecules (as the size of the molecule).

Interaction parameters similar to the virial coefficients
Reason A´, B´ it´s same q1 and q2 and Activity coefficient at infinite dilution

q1 =q2
Gibbs Energy in excess associated with the molar fractions. Using for solutions polar compounds or solvents no polar.
Activity Coefficients
Limit condition:
GE=0 if x1 or x2
Can be easily extended to multicomponent mixtures.
Doesn´t apply to Liquid-liquid equilibrium.
Wilson parameters report to binary, ternary and quaternary system
Parameter alpha related non random in mixture. The components fallow pattern defined by the
local composition.
Mixture is random (Equal Margules)
Property relationships for mixtures:
Molar Excess:

Molar Partial:
For liquid disolutions:
Integrate from the pure state to its state in the solution at a molar fraction x
The necessary condition for that a liquid phase is in equilibrium is that it behaves like an ideal solution.
The activity coefficient can related to the excess Gibbs energy since ln(lamba) is a partial property regarding GE/ RT
Using Euler Theorem for homogeneous functions:

Dividing by n (moles)
Additionability equation
M of a mixture it´s obtained by aggregation of partial properties of its components with a weight proportional to amount present
For binary solution:
Thermody. Functs:
Raoult´s law
Data and results
Show that:
Smith And Van Ness, Introducción a la Termodinámica en Ingenieria Química
Tester J, Modell M, Thermodynamics and its applications
Reference state
Gibbs molar
The reference State could be:

For most solutions a/x is not unit.
If M = (V, U, S or G)
By analogy, excess mixing functions: Whit M=B
use if one of the components doesn´t exist at pure liquid at T and P in question.
Pure component standard state, rational basis at T and P of mixture

Unit molality
Infinity dilution
Variation a miscible A-B solution
For Solute A, there are two different states:
For Solvent B, only one:
Base in mole fractions. In place of mole fractions we introduce molality (m) as composition parameter
Reference stady, at same P, T and sate aggregation as the mixture.
molality based (activity coefficients)
Limit by:
This relationship allows to obtain the effects to T and P
Properties for Methyl Ethyl Cetone(1)/Toluene(2)
Lewis Randall
Full transcript