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VLE-1

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equilibrium?

Equilibrium is the static condition inwhich no change occur in the

macroscopic properties of a system withtime

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Raoult’s lawRaoult’s law states that the partial pressure is equal to product of vapor

pressure and mole fraction in liquid phase.

p1=x 1.p10Where,

p 1 -partial pressure of component p 1 0 -vapour pressure of pure componentx1 -mole fraction of component in liquid phase

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(a) a solution that shows positive deviation from Raoult's law

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(b) a solution that shows negative deviation from Raoult's law.

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Dalton’s law

P total = p 1+ p2Where,

P total -Total pressure p1 ,p 2 -Partial pressure of component.

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Composition of liquid phase :

x1= p 1 p10

= partial pressure of component vapour pressure of pure component

!omposition in "aseous phase #$ 1= p 1 P

= partial pressure of component total pressure%aoult&s la' (ecomes

$ iP=x iP isat )i=1,2,* ..nWhere#

$i = apor-phase mole fraction.xi = iquid-phase mole fraction.Pi = apor pressure of pure species i at the T of the s$stem.$i P = Partial pressure of species i.

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VLE ! "odified Raoult’s Law

$i P = xi /i P isat ) i= 1,2, ..,

Where/i = ctivit$ coefficient.

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#-$-! dia%ram& oilin% point dia%ram

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Effect of pressure on VLE #he hi%h pressuredia%rams are a ove low pressure.

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Equili rium Dia%ramVapor composition is drawn a%ainst liquid comp at

constant pressure. Vapour is alwa!s rich in morevolatile component the curve lies a ove the dia%onalline.

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Effect of var!in% pressure on equili riumdia%ram

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'-$-! Dia%ram

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u"acit$# 3t is derived from atin, expressed asfleetness or escapin" tendenc$. 3t is usedto stud$ extensivel$ phase and chemical reactionequili(rium.

G = RT ln f + ɵ

- Is an constant depends on temperature and natureɵof gas.

fu"acit$ has same units as pressure for an ideal "as.

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u"acit$ coefficient ) ) :ɸ u"acit$ coefficient is defined as the ratio of fu"acit$of component to its pressure.

=f/P ɸ

- 3s the measure of non ideal (ehavior of the "as.ɸ

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ctivit$)a #3t is defined as the fu"acit$ of the existin" conditionto the standard state fu"acit$

a=f f o

ctivit$ coefficient #3t measure the extent to 'hich real solution depart from

idealit$.ln/4=(x45ln/4=(x45

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(ctivit! coefficient equations

Wohl&s three suffix equation 6ar"ules equation an laar equation Wilson equation on random t'o liquid ) %T equation 7niversal quasi 8chemical )7 397 ! equation 7niversal functional activit$ coefficient )7 3 !

method

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Consistenc! test for VLE data

7sin" slope of ln/ curves 7sin" data at mid point %edlich 8:ister method 7sin" the coexistence equation 7sin" partial pressure data

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Thank You