Multicomponent systems Doba Jackson, Ph.D. Huntingdon College

Problem 1: Acetone has a normal boiling point of 56. 2 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.

Problem 2: The vapor pressure of bromine is 133 torr at 20. C and 48 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.

Chemical Potentials of Liquids and liquid mixtures Θ is pressure at 1 bar * is pressure of pure A Rauolt’s Law Rauolt’s law states that the chemical potential of the liquid is altered by the presence of a solute. The amount of the deviation is based on the mole fraction of the solute.

Ideal Solutions Ideal solutions are solutions that obey Rauolt’s law throughout its composition range from pure A to pure B.

Rauolt’s Law is observed when two solutions have similar structures Obey’s Rauolt’s Law Does not obey’s Rauolt’s Law

Dilute solutions typically do not obey Rauolt’s Law but follows Henry’s Law Θ is pressure at 1 bar * is pressure of pure A Henry’s Law Henry’s law states that the chemical potential of the liquid is altered by the presence of a solute. The amount of the deviation is based on the mole fraction of the solute.

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 Hg 1.00 mol + 15.0 mol x 23.76 mm Hg 15.0 mol =

Basis for Rauolt’s and Henry’s Law Rauolt’s Law Henry’s Law

General model of solutions

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?

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.

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

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

Liquid-only Phase diagrams Upper consolute temp. (Tuc)- Is the temperature at which both liquids are miscible. Inside the circle, two phases exist. Each composition is given by the lever rule. Hexane-Nitrobenzene

Liquid-only Phase diagrams Water-Triethanolamine Lower consolute temp. (Tlc)- Is the temperature at which both liquids are miscible. Inside the circle, two phases exist. Each composition is given by the lever rule.

Liquid-only Phase diagrams Lower consolute temp. (Tlc)- Is the temperature at which both liquids are miscible. Inside the circle, two phases exist. Each composition is given by the lever rule. Water-Nicotine solution

Liquid-only Phase diagrams

A temperature-composition diagram in which boiling occurs before the solution becomes miscible

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

Osmosis Osmosis: the spontaneous passage of a pure solvent into a solution while separated by a semi-permeable membrane. - Cell membrane transport - Dialysis - Blood Transfusions - Osmometry (M.W. determinations) Osmotic Pressure (π): the pressure required to stop the influx of solvent.

Calculation of Osmotic Pressure Fundamental Equation; Assume const. Temperature Change in pressure is due to solute concentration in the solution.

Calculation of Osmotic Pressure Assume the solute concentration is small Molar Concentration