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# PPT: Vapour - Liquid Equilibria Mechanical Engineering Notes | EduRev

## Mechanical Engineering : PPT: Vapour - Liquid Equilibria Mechanical Engineering Notes | EduRev

``` Page 1

OUTLINE
1. The Nature of Equilibrium
2. Duhem’s Theorem
3. Simple Models for VLE
4. VLE by Modified Raoult’s Law
5. VLE from K-value Correlations
Page 2

OUTLINE
1. The Nature of Equilibrium
2. Duhem’s Theorem
3. Simple Models for VLE
4. VLE by Modified Raoult’s Law
5. VLE from K-value Correlations
1. The Nature of Equilibrium
• Equilibrium is a static condition in which no
changes occur in the macroscopic properties
of a system with time.
– Eg: An isolated system consisting of liquid & vapor
phase reaches a final state wherein no tendency
exists for change to occur within the system. The
temperature, pressure and phase compositions
reach final values which thereafter remain fixed.

Page 3

OUTLINE
1. The Nature of Equilibrium
2. Duhem’s Theorem
3. Simple Models for VLE
4. VLE by Modified Raoult’s Law
5. VLE from K-value Correlations
1. The Nature of Equilibrium
• Equilibrium is a static condition in which no
changes occur in the macroscopic properties
of a system with time.
– Eg: An isolated system consisting of liquid & vapor
phase reaches a final state wherein no tendency
exists for change to occur within the system. The
temperature, pressure and phase compositions
reach final values which thereafter remain fixed.

The Nature of Equilibrium
• At microscopic level, conditions are not static.
– Molecules with high velocities near the interface
overcome surface forces and pass into the other
phase.
– But the average rate of passage of molecules is
the same in both directions & no net interphase
transfer of material occurs.

Page 4

OUTLINE
1. The Nature of Equilibrium
2. Duhem’s Theorem
3. Simple Models for VLE
4. VLE by Modified Raoult’s Law
5. VLE from K-value Correlations
1. The Nature of Equilibrium
• Equilibrium is a static condition in which no
changes occur in the macroscopic properties
of a system with time.
– Eg: An isolated system consisting of liquid & vapor
phase reaches a final state wherein no tendency
exists for change to occur within the system. The
temperature, pressure and phase compositions
reach final values which thereafter remain fixed.

The Nature of Equilibrium
• At microscopic level, conditions are not static.
– Molecules with high velocities near the interface
overcome surface forces and pass into the other
phase.
– But the average rate of passage of molecules is
the same in both directions & no net interphase
transfer of material occurs.

Measures of Composition
1. Mass fraction: the ratio of the mass of a particular chemical
species in a mixture or solution to the total mass of mixture or
solution.

2. Mole fraction: the ratio of the number of moles of a
particular chemical species in a mixture or solution to the number
of  moles of mixture or solution.
m
m
m
m
x
i i
i
?
?
? ?
n
n
n
n
x
i i
i
?
?
? ?
Page 5

OUTLINE
1. The Nature of Equilibrium
2. Duhem’s Theorem
3. Simple Models for VLE
4. VLE by Modified Raoult’s Law
5. VLE from K-value Correlations
1. The Nature of Equilibrium
• Equilibrium is a static condition in which no
changes occur in the macroscopic properties
of a system with time.
– Eg: An isolated system consisting of liquid & vapor
phase reaches a final state wherein no tendency
exists for change to occur within the system. The
temperature, pressure and phase compositions
reach final values which thereafter remain fixed.

The Nature of Equilibrium
• At microscopic level, conditions are not static.
– Molecules with high velocities near the interface
overcome surface forces and pass into the other
phase.
– But the average rate of passage of molecules is
the same in both directions & no net interphase
transfer of material occurs.

Measures of Composition
1. Mass fraction: the ratio of the mass of a particular chemical
species in a mixture or solution to the total mass of mixture or
solution.

2. Mole fraction: the ratio of the number of moles of a
particular chemical species in a mixture or solution to the number
of  moles of mixture or solution.
m
m
m
m
x
i i
i
?
?
? ?
n
n
n
n
x
i i
i
?
?
? ?
Measures of Composition
3. Molar concentration: the ratio of the mole fraction of a
particular chemical species in a mixture or solution to the molar
volume of mixture or solution.

4. Molar mass of mixture/solution: mole-fraction-
weighted sum of the molar masses of all species present.
q
n
V
x
C
i i
i
?
? ?
i
i
i
M x M
?
?
?
i
n
?
? q
Molar  flow rate
Volumetric flow rate
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## Thermodynamics

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