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What is equilibrium?

  At equilibrium no driving force for energyor mass transfer .

  Equilibrium is the static condition inwhich no change occur in themacroscopic 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=x1.p10

Where,

 p1-partial pressure of component p10-vapour pressure of pure component

x1 -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

Ptotal = p1+ p2Where,

Ptotal  -Total pressure p1 ,p2 -Partial pressure of component.

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Composition of liquid phase :

x1= p1 p10

  =  partial pressure of component vapour pressure of pure component

!omposition in "aseous phase #$ 1= p1 P

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

$iP=xiPisat  )i=1,2,*..n

Where#

$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 by odified Raoult’s Law

$i P = xi /i Pisat ) i= 1,2,..,

Where

/i = ctivit$ coefficient.

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!"#"y dia$ram%boilin$ point dia$ram

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Effect of pressure on VLE !he hi$h pressure

dia$rams are above low pressure.

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Equilibrium Dia$ramVapor composition is drawn a$ainst liquid comp at

constant pressure. Vapour is always rich in morevolatile component the curve lies above the dia$onal

line.

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Effect of varyin$ pressure on equilibrium

dia$ram

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&"#"y Dia$ram