Solution Thermodynamics: Theory
Chemical Engineering Thermodynamics
Lecturer: Zhenxi Jiang (Ph.D. U.K.)
School of Chemical Engineering
1
Chapter 12
Solution Thermodynamics: Application
2
12.2 Models for the Excess Gibbs Energy
In general G E /RT is a function of T , P , and composition, but for liquids at low to moderate pressures it is a very weak function of P. Therefore the pressure dependence of activity coefficients is usually neglected. Thus, for data at constant T:
G
E
RT
g x x
1 2 x
N
)
(const T )
The Margules equation, Eq. (12.9), is an example of this functionality.
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12.2 Models for the Excess Gibbs Energy
A number of other equations are in common use for correlation of activity coefficients. For binary systems (species 1 and 2) the function most often represented by an equation is which may be expressed as a power series in x
1
:
E
G / x x RT
1 2
,
G
E x x RT
1 2 a bx
1
cx
1
2 (const T )
4
12.2 Models for the Excess Gibbs Energy
Because x
2
=1x
1
, mole fraction x
1 serves as the single independent variable. An equivalent power series with certain advantages is known as the Redlich/Kister expansion:
G
E x x RT
1 2
(
1
x
2
)
(
1
x
2
)
2
In application, different truncations of this series are
(12.14)
5
12.2 Models for the Excess Gibbs Energy
Because x
2
=1x
1
, mole fraction x
1 serves as the single independent variable. An equivalent power series with certain advantages is known as the Redlich/Kister expansion:
G
E x x RT
1 2
(
1
x
2
)
(
1
x
2
)
2
In application, different truncations of this series are
(12.14)
6
12.2 Models for the Excess Gibbs Energy
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12.2 Models for the Excess Gibbs Energy
8
12.2 Models for the Excess Gibbs Energy
9
12.2 Models for the Excess Gibbs Energy
Local Composition Models
10
12.2 Models for the Excess Gibbs Energy
Local Composition Models
11
12.2 Models for the Excess Gibbs Energy
Local Composition Models
12
12.2 Models for the Excess Gibbs Energy
Local Composition Models
13
12.3 Property Changes of Mixing
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12.3 Property Changes of Mixing
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12.3 Property Changes of Mixing
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12.3 Property Changes of Mixing
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12.3 Property Changes of Mixing
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12.3 Property Changes of Mixing
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12.3 Property Changes of Mixing
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12.3 Property Changes of Mixing
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12.3 Property Changes of Mixing
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12.3 Property Changes of Mixing
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12.3 Property Changes of Mixing
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12.3 Property Changes of Mixing
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12.3 Property Changes of Mixing
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