Excess Thermodynamic Properties

X. Rosario Rajkumar Department of Humanities and Science

Oxford Engineering College Tiruchirappalli – 620 009

at Cauvery College for Women, Tiruchirappalli

December 16, 2011 (Friday)

Innovation is our strength

Like dissolves like

Sugar in Water --- Dissolves

Sugar in Kerosene --- Does not dissolve

NaCl in Water

Ion-Dipole Interactions

Liquid water

O H

H

O

H

H

O

H

H

O

H

H

O

HH

OH H

Water molecules in vapour

Dipole-Dipole Interactions(Keesom Forces)

Edip-dip = 2mA2mB

2/3RAB2kT

Alcohol and water

London Forces

Polarized molecule

Neighbouringmolecue

BenzeneIodine

EABdisp = [3aAaBIAIB/2(IA+IB)] /

(1/R6)

Hydrogen Bonding

H F H F H F

Parameters

Excess volume of mixing, Heat of mixing

Internal Pressure usingDensity and viscosity

Adiabatic compressibility

Ks =1 / (U2 x d )

Gibbs Free Energy of Mixing using vapour pressures of liquids andLiquid mixtures

Force ModelEnergy, KJmol-1

Example

Ionic 400-4000 NaCl

Covalent 150-1100 H-H

Metallic 75-1000 Au

+

+

-

-

+ electrons +

+ + + +

+

+

+ + +

+ + +

e e e

e e e

Force ModelEnergy, kJmol-1 Example

Ion-dipole 40-600Na+ & H2O

Dipole-dipole 5-25

HCl and HCl

H-bond O-H ------F-H 10-40 H2O & HF

London dispersion 0.05-40

Xenon & Xenon

+ d- d+

d- d+ d- d+

d- d+ d- d+

Ideal gas?

• No intermolecular interaction

• Obeys ideal gas equation, PV = nRT

• At low P and at high T, a real gas tends to to ideal gas

Thermodynamics of SolutionsProperties of Ideal Solutions:1. There is no volume change when an

ideal solution is formed from its pure components

2. There is no evolution or absorption of heat during the formation of an ideal solution

3. An ideal solution obeys Raoult’s law

pi = xi pio

pi = partial vapour pressure of ixi = mole fraction of I in the solution

pio = vapour pressure of pure component i

4. In an ideal solution the intermolecular interactions between like molecules is equal to that of unlike molecules

Consider a binary solution containing liquid A and liquid B:

Interaction between A & A (like moleules)

--- A-AInteraction between B & B (like moleules)

--- B-BInteraction between A & B (unlike moleules)

--- A-BIn an ideal solution,

A-A or B-B = A-B

In a non-ideal solution,A-A or B-B not equal to A-B

100mL of alcohol + 100mL of water = ----- mL of solution

Why?•Rupture of H-bonds in alcohol by the addition of water• Breaking up of H-bonds in water by the addition of alcohol• Formation of H-bonds between alcohol and water• Dipole-dipole interactions

VE = (volume after mixing) – (volume before mixing)

Excess volume of mixing Ethanol + Water

VE ={ [XA MA + XB MB ] / dAB}- [ XA MA / dA] + [ XB M B / dB ]

VE = Excess Volume of Mixing of two liquids A and B (non- reacting, homogeneous)XA = Mole fraction of liquid A in the solution of A and BXB = Mole fraction of liquid BMA and MB = respective molar masses of A and BdA = density of AdB = density of BdAB = density of the liquid mixture

PYKNOMETER

R D BOTTLE

Experimental Methods

Measurement of Density of liquid and Liquid mixtures using Pyknometer or RD Bottle or Densimeter.Measurement of Heat of Mixing by Calorimetry.Measurement of ultrasonic velocity in

liquids and liquid mixtures by interferometry.

Vapour pressure by Isoteniscope

Deviation in isentropic copressibility (Ks)

• Ks = Ks,mix – ( x1Ks1 + x2Ks2)• Ks,mix = isentrpic compressiblity of the liquid • mixture• Ks1 and Ks2 are respective isentropic

comressibilities of liquid 1 and 2• X1 and X2 are respective mole fractions

ULTRSONIC INTERFEROMETER

Dewar Flask

• Dewar Flask

Q = m s T + w T

H = Heat of solution

Density of liquids/liquid mixtures

• Density = (m/m0)xdo at T• m = mass of certain volume of liquid• m0 = mass of same volume of water

• d0 = density of water at T (from Tables)

Thermodynamic parameters

• I. Prigogine 1977 Nobel Prize winner

• Best low priced Calorimeter ? Dewar flask * Most accurate thermometer to readthe difference in temperatures

? Beckmann thermo-meter

ISOTENISCOPE

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Attractive Inter-Human Interactions

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?

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