Multicomponent systems Doba Jackson, Ph.D. Huntingdon College.
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Transcript of Multicomponent systems Doba Jackson, Ph.D. Huntingdon College.
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Multicomponent systemsDoba Jackson, Ph.D.
Huntingdon College
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Problem 1: Acetone has a normal boiling point of 56.2*C and a molar enthalpy of vaporization of 31.97 kJ/mol. Calculate the equilibrium vapor pressure of acetone at 20.0*C.
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Problem 2: The vapor pressure of bromine is 133 torr at 20.0*C and 48.1 torr at 0.00*C. Calculate the enthalpy of vaporization of bromine.
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Chemical Potentials of Liquids and liquid mixturesP
= RTLnPA
A AA
**
P= RTLn
PA
A AA
Θ is pressure at 1 bar
* is pressure of pure A
Rauolt’s Law*
A A AP P*A
AA
P
P
*= RTLnA A A
Rauolt’s law states that the chemical potentialof the liquid is altered by the presence of a solute.The amount of the deviation is based on the molefraction of the solute.
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Ideal Solutions
• Ideal solutions are solutions that obey Rauolt’s law throughout its composition range from pure A to pure B.
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Rauolt’s Law is observed when two solutions have similar structures
Obey’s Rauolt’s Law Does not obey’s Rauolt’s Law
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Dilute solutions typically do not obey Rauolt’s Law but follows Henry’s Law
P= RTLn
PA
A AA
**
P= RTLn
PA
A AA
Θ is pressure at 1 bar
* is pressure of pure A
Henry’s LawA A AP K AA
A
P
K
**
= RTLn A AA A
A
K
P
Henry’s law states that the chemical potentialof the liquid is altered by the presence of a solute.The amount of the deviation is based on the molefraction of the solute.
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Vapor-Pressure Lowering of Solutions: Raoult’s Law
The vapor pressure of pure water at 25 °C is 23.76 mm Hg. What is the vapor pressure of a solution made from 1.00 mol glucose in 15.0 mol of water at 25 °C? Glucose is a nonvolatile solute.
Psoln = Psolv Xsolv
= 22.3 mm Hg1.00 mol + 15.0 mol
x23.76 mm Hg 15.0 mol=
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Basis for Rauolt’s and Henry’s Law
*A A AP P
A A AP K
Rauolt’s Law
Henry’s Law
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General model of solutions
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Problem 5.24a
• It is found that the normal boiling point of a binary solution of A and B with XA=.6589 is 88*C. At this temperature the vapor pressures of pure A and B are 129.6 kPa and 51.60 kPa, respectively.
• (a) Is the solution Ideal?• (b) What is the composition of the vapor
above the solution mixture?
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Temperature-composition diagrams
• Distillation- separation of mixtures by withdrawing the more volatile component
in the vapor phase.
• Theoretical plates- number of vaporization-condensation steps required to achieve a given composition.
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Theoretical Plates
# of Theoretical Plates depend on several factors:
- Temperature- Distillation Apparatus- Composition
- Vaporization temp. difference- Azeotropes
-Amount of each phase can be determined by the lever rule
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Types of Phase Diagrams• Vapor Pressure-Composition Diagrams
– Upper Liquid Phase (P=1)– Bi-Phase intermediate (P=2)– Lower Vapor Phase (P=1)
• Liquid-Composition Diagrams– Upper vapor Phase– Bi-Phase intermediate– Lower vapor Phase
Two miscible liquids
Two partially miscible liquids
Azeotropic composition
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Liquid-only Phase diagrams
Upper consolute temp. (Tuc)-
Is the temperature at whichboth liquids are miscible.
Inside the circle, two phasesexist.
Each composition is givenby the lever rule.
Hexane-Nitrobenzene
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Liquid-only Phase diagrams
Lower consolute temp. (Tlc)-
Is the temperature at whichboth liquids are miscible.
Inside the circle, two phasesexist.
Each composition is givenby the lever rule.
Water-Triethanolamine
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Liquid-only Phase diagrams
Lower consolute temp. (Tlc)-
Is the temperature at whichboth liquids are miscible.
Inside the circle, two phasesexist.
Each composition is givenby the lever rule.
Water-Nicotine solution
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Liquid-only Phase diagrams
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A temperature-composition diagram in which boiling occurs before the
solution becomes miscible
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Colligative Properties
• Colligative Properties- properties of solutions that depend only on the number of molecules present in a volume of solvent and not on the identity of the solute.
–Vapor Pressure lowering–Boiling Point Elevation–Freezing Point Depression–Osmosis
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Osmosis
Osmosis: the spontaneous passage of a pure solvent intoa solution while separated by asemi-permeable membrane.
- Cell membrane transport - Dialysis - Blood Transfusions - Osmometry (M.W. determinations)
Osmotic Pressure (π): the pressure required to stop the influx of solvent.
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Calculation of Osmotic Pressure
* P
A A mPG p p V dP
* P
A A mPp p V dP
Fundamental Equation;Assume const. Temperature
* = RTLnA A Ap p
Change in pressure is due to soluteconcentration in the solution.
RTLnP
m APV dP
RTLn 1m BV
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Calculation of Osmotic Pressure
RTLn 1m BV 1 B BLn
RTm BV B
BT
n
n
RT Bm
T
nV
n
T mn V VRT BV n
RT Bn
V
RT M Bn M
V
Molar Concentration
Assume the solute concentration is small