1 © 2006 brooks/cole - thomson chemistry and chemical reactivity 6th edition john c. kotz paul m....
TRANSCRIPT
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© 2006 Brooks/Cole - Thomson
Chemistry and Chemical Reactivity 6th Edition
John C. Kotz Paul M. Treichel
Gabriela C. Weaver
CHAPTER 13
Intermolecular Forces, Liquids, and Solids
© 2006 Brooks/Cole Thomson
Lectures written by John Kotz
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WHYWHY??
• Why is water usually a liquid and not a gas?
• Why does liquid water boil at such a high temperature for such a small molecule?
• Why does ice float on water?
• Why do snowflakes have 6 sides?
• Why is I2 a solid whereas Cl2 is a gas?
• Why are NaCl crystals little cubes?
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Liquids, Solids Liquids, Solids & Intermolecular Forces& Intermolecular Forces
Chap. 13Chap. 13
Liquids, Solids Liquids, Solids & Intermolecular Forces& Intermolecular Forces
Chap. 13Chap. 13
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Inter-Inter-moleculamolecular Forcesr Forces
Inter-Inter-moleculamolecular Forcesr Forces
Have studied Have studied INTRAINTRAmolecular molecular forces—the forces holding forces—the forces holding atoms together to form atoms together to form molecules.molecules.
Now turn to forces between Now turn to forces between molecules —molecules — INTERINTERmolecular forces. molecular forces.
Forces between molecules, Forces between molecules, between ions, or between between ions, or between molecules and ions.molecules and ions.
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Ion-Ion ForcesIon-Ion Forcesfor comparison of for comparison of
magnitudemagnitude
Ion-Ion ForcesIon-Ion Forcesfor comparison of for comparison of
magnitudemagnitude
NaNa++—Cl—Cl-- in salt in salt
These are the These are the strongest forces.strongest forces.
Lead to solids with Lead to solids with high melting high melting temperatures.temperatures.
NaCl, mp = 800 NaCl, mp = 800 ooCC
MgO, mp = 2800 MgO, mp = 2800 ooCC
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Covalent Bonding ForcesCovalent Bonding Forcesfor comparison of for comparison of
magnitudemagnitude
Covalent Bonding ForcesCovalent Bonding Forcesfor comparison of for comparison of
magnitudemagnitude
C–H, 413 kJ/molC–H, 413 kJ/mol
C=C, 610 kJ/molC=C, 610 kJ/mol
C–C, 346 kJ/molC–C, 346 kJ/mol
CN, 887 kJ/molCN, 887 kJ/mol
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Attraction Between Attraction Between Ions and Permanent Ions and Permanent
DipolesDipoles
Attraction Between Attraction Between Ions and Permanent Ions and Permanent
DipolesDipoles
Water is highly polar Water is highly polar and can interact and can interact with positive ions to with positive ions to give give hydratedhydrated ions in water.ions in water.
HH
water dipole
••
••
O-
+
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Attraction Between Attraction Between Ions and Permanent Ions and Permanent
DipolesDipoles
Attraction Between Attraction Between Ions and Permanent Ions and Permanent
DipolesDipoles
Water is highly polar Water is highly polar and can interact and can interact with positive ions to with positive ions to give give hydratedhydrated ions in water.ions in water.
HH
water dipole
••
••
O-
+
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Attraction Between Attraction Between Ions and Permanent Ions and Permanent
DipolesDipoles
Attraction Between Attraction Between Ions and Permanent Ions and Permanent
DipolesDipoles
Many metal ions are hydrated. Many metal ions are hydrated. This is the reason metal salts This is the reason metal salts dissolve in waterdissolve in water..
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Attraction between ions and dipole depends on Attraction between ions and dipole depends on ion chargeion charge and and ion-dipole distanceion-dipole distance..
Measured by ∆H for MMeasured by ∆H for Mn+n+ + H + H22O --> [M(HO --> [M(H22O)O)xx]]n+n+
-1922 kJ/mol-1922 kJ/mol -405 kJ/mol-405 kJ/mol -263 kJ/mol-263 kJ/mol
Attraction Between Attraction Between Ions and Permanent Ions and Permanent
DipolesDipoles
Attraction Between Attraction Between Ions and Permanent Ions and Permanent
DipolesDipoles
OH
H+
-• • • O
H
H+
-• • • O
H
H+
-• • •
Na+Mg2+
Cs+
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Dipole-Dipole Dipole-Dipole ForcesForces
Dipole-Dipole Dipole-Dipole ForcesForces
Such forces bind molecules having Such forces bind molecules having permanent dipoles to one another.permanent dipoles to one another.
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Dipole-Dipole Dipole-Dipole ForcesForces
Dipole-Dipole Dipole-Dipole ForcesForces
Influence of dipole-dipole forces is seen in Influence of dipole-dipole forces is seen in the boiling points of simple molecules.the boiling points of simple molecules.
CompdCompd Mol. Wt.Mol. Wt. Boil Boil PointPoint
NN22 2828 -196 -196 ooCC
COCO 2828 -192 -192 ooCC
BrBr22 160160 59 59 ooCC
IClICl 162162 97 97 ooCC
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Hydrogen BondingHydrogen BondingHydrogen BondingHydrogen Bonding
A special form of dipole-dipole attraction, A special form of dipole-dipole attraction, which enhances dipole-dipole attractions.which enhances dipole-dipole attractions.
H-bonding is strongest when X and Y are H-bonding is strongest when X and Y are N, O, N, O, or For F
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H-Bonding Between H-Bonding Between Methanol and WaterMethanol and WaterH-Bonding Between H-Bonding Between Methanol and WaterMethanol and Water
H-bondH-bondH-bondH-bond--
++
--
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H-Bonding Between H-Bonding Between Two Methanol Two Methanol
MoleculesMolecules
H-Bonding Between H-Bonding Between Two Methanol Two Methanol
MoleculesMolecules
H-bondH-bondH-bondH-bond
--++
--
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H-Bonding Between H-Bonding Between Ammonia and WaterAmmonia and WaterH-Bonding Between H-Bonding Between Ammonia and WaterAmmonia and Water
H-bondH-bondH-bondH-bond
--
++ --
This H-bond leads to the formation of This H-bond leads to the formation of NHNH44
++ and OH and OH--
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Hydrogen Bonding in HHydrogen Bonding in H22OOHydrogen Bonding in HHydrogen Bonding in H22OO
H-bonding is especially H-bonding is especially strong in water strong in water becausebecause
• the O—H bond is very the O—H bond is very polarpolar
• there are 2 lone pairs there are 2 lone pairs on the O atomon the O atom
Accounts for many of Accounts for many of water’s unique water’s unique properties.properties.
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Hydrogen Bonding in HHydrogen Bonding in H22OOHydrogen Bonding in HHydrogen Bonding in H22OO
Ice has open Ice has open lattice-like lattice-like structure.structure.
Ice density is Ice density is < liquid.< liquid.
And so solid And so solid floats on floats on water.water.
Snow flake: www.snowcrystals.com
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Hydrogen Bonding in HHydrogen Bonding in H22OOHydrogen Bonding in HHydrogen Bonding in H22OO
Ice has open lattice-like structure.Ice has open lattice-like structure.
Ice density is < liquid and so solid floats on water.Ice density is < liquid and so solid floats on water.
One of the VERY few One of the VERY few substances where substances where solid is LESS DENSE solid is LESS DENSE than the liquid.than the liquid.
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A A consequeconseque
nce of nce of hydrogen hydrogen bondingbonding
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Hydrogen Bonding in HHydrogen Bonding in H22OOHydrogen Bonding in HHydrogen Bonding in H22OOH bonds ---> abnormally high specific heat capacity of water (4.184 H bonds ---> abnormally high specific heat capacity of water (4.184
J/g•K)J/g•K)
This is the reason water is used to put out fires, it is the reason This is the reason water is used to put out fires, it is the reason lakes/oceans control climate, and is the reason thunderstorms lakes/oceans control climate, and is the reason thunderstorms release huge energy.release huge energy.
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Hydrogen BondingHydrogen BondingHydrogen BondingHydrogen Bonding
H bonds leads to H bonds leads to abnormally high abnormally high boiling point of boiling point of water.water.
See Screen 13.7See Screen 13.7
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Boiling Points of Boiling Points of Simple Hydrogen-Simple Hydrogen-
Containing Containing CompoundsCompounds
Active Figure 13.8Active Figure 13.8
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Hydrogen Bonding in Hydrogen Bonding in BiologyBiology
Hydrogen Bonding in Hydrogen Bonding in BiologyBiology
H-bonding is especially strong in biological H-bonding is especially strong in biological systems — such as DNA. systems — such as DNA.
DNA — helical chains of phosphate groups DNA — helical chains of phosphate groups and sugar molecules. Chains are helical and sugar molecules. Chains are helical because of tetrahedral geometry of P, C, because of tetrahedral geometry of P, C, and O.and O.
Chains bind to one another by specific Chains bind to one another by specific hydrogen bonding between pairs of Lewis hydrogen bonding between pairs of Lewis bases.bases.
——adenine with thymineadenine with thymine
——guanine with cytosineguanine with cytosine
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Portion of a Portion of a DNA chainDNA chain
Double helix Double helix of DNAof DNA
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Base-Pairing through H-Base-Pairing through H-BondsBonds
Base-Pairing through H-Base-Pairing through H-BondsBonds
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Double Double Helix of Helix of
DNADNA
Double Double Helix of Helix of
DNADNA
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Discovering the Double Discovering the Double HelixHelix
Discovering the Double Discovering the Double HelixHelix
James Watson James Watson and Francis and Francis Crick, 1953Crick, 1953
Rosalind Rosalind Franklin, 1920-Franklin, 1920-19581958
Maurice Wilkins, Maurice Wilkins, 1916 - 20041916 - 2004
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Hydrogen Bonding in Hydrogen Bonding in BiologyBiology
Hydrogen Bonding in Hydrogen Bonding in BiologyBiology
Hydrogen bonding and base pairing in DNA.Hydrogen bonding and base pairing in DNA.
See Screen 13.6See Screen 13.6
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FORCES INVOLVING FORCES INVOLVING INDUCED DIPOLESINDUCED DIPOLES
FORCES INVOLVING FORCES INVOLVING INDUCED DIPOLESINDUCED DIPOLES
How can non-polar molecules such as OHow can non-polar molecules such as O2 2 and Iand I22 dissolve in water? dissolve in water?
The water dipole The water dipole INDUCESINDUCES a a dipole in the Odipole in the O22 electric cloud. electric cloud.
Dipole-induced Dipole-induced dipoledipole
Dipole-induced Dipole-induced dipoledipole
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FORCES INVOLVING FORCES INVOLVING INDUCED DIPOLESINDUCED DIPOLES
FORCES INVOLVING FORCES INVOLVING INDUCED DIPOLESINDUCED DIPOLES
Solubility increases with mass the gasSolubility increases with mass the gas
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FORCES INVOLVING FORCES INVOLVING INDUCED DIPOLESINDUCED DIPOLES
FORCES INVOLVING FORCES INVOLVING INDUCED DIPOLESINDUCED DIPOLES
• Process of inducing Process of inducing a dipole is a dipole is polarizationpolarization
• Degree to which Degree to which electron cloud of an electron cloud of an atom or molecule atom or molecule can be distorted in can be distorted in its its polarizabilitypolarizability..
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IM FORCES — INDUCED DIPOLESIM FORCES — INDUCED DIPOLESIM FORCES — INDUCED DIPOLESIM FORCES — INDUCED DIPOLES
Consider IConsider I22 dissolving dissolving in ethanol, in ethanol, CHCH33CHCH22OH.OH.
OH
-
+
I-I
R-
+
OH
+
-
I-I
R
The alcohol The alcohol temporarily temporarily creates or creates or INDUCESINDUCES a a dipole in Idipole in I22..
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FORCES INVOLVING FORCES INVOLVING INDUCED DIPOLESINDUCED DIPOLES
FORCES INVOLVING FORCES INVOLVING INDUCED DIPOLESINDUCED DIPOLES
Formation of a dipole in two nonpolar IFormation of a dipole in two nonpolar I22 molecules.molecules.
Induced dipole-Induced dipole-induced dipoleinduced dipoleInduced dipole-Induced dipole-induced dipoleinduced dipole
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FORCES INVOLVING FORCES INVOLVING INDUCED DIPOLESINDUCED DIPOLES
FORCES INVOLVING FORCES INVOLVING INDUCED DIPOLESINDUCED DIPOLES
The induced forces between IThe induced forces between I22 molecules are molecules are
very weak, so solid Ivery weak, so solid I22 sublimessublimes (goes from (goes from a solid to gaseous molecules).a solid to gaseous molecules).
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FORCES INVOLVING FORCES INVOLVING INDUCED DIPOLESINDUCED DIPOLES
FORCES INVOLVING FORCES INVOLVING INDUCED DIPOLESINDUCED DIPOLES
The magnitude of the induced dipole depends The magnitude of the induced dipole depends on the tendency to be distorted. on the tendency to be distorted.
Higher molec. weight ---> larger induced Higher molec. weight ---> larger induced dipoles.dipoles.
MoleculeMolecule Boiling Point Boiling Point ((ooC)C)
CHCH44 (methane) (methane) - 161.5- 161.5
CC22HH66 (ethane) (ethane) - 88.6 - 88.6
CC33HH88 (propane) (propane) - 42.1- 42.1
CC44HH1010 (butane) (butane) - 0.5- 0.5
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Boiling Points of Boiling Points of HydrocarbonsHydrocarbons
Note linear relation between bp and molar mass.
CHCH44
CC22HH66
CC33HH88
CC44HH1010
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Summary of Summary of Intermolecular ForcesIntermolecular Forces
Summary of Summary of Intermolecular ForcesIntermolecular Forces
• Ion-dipole forcesIon-dipole forces
• Dipole-dipole forcesDipole-dipole forces–Special dipole-dipole force: Special dipole-dipole force: hydrogen bondshydrogen bonds
• Forces involving nonpolar Forces involving nonpolar molecules: molecules: induced forcesinduced forces
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Intermolecular ForcesIntermolecular Forces
Figure 13.13Figure 13.13
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LiquidsLiquidsSection 13.5Section 13.5
LiquidsLiquidsSection 13.5Section 13.5
In a liquidIn a liquid•• molecules are in molecules are in
constant motionconstant motion
•• there are appreciable there are appreciable intermolec. forcesintermolec. forces
•• molecules close molecules close togethertogether
•• Liquids are almost Liquids are almost incompressibleincompressible
•• Liquids do not fill the Liquids do not fill the containercontainer
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LiquidsLiquids
The two key properties we need to describe The two key properties we need to describe are are EVAPORATIONEVAPORATION and its opposite— and its opposite—CONDENSATIONCONDENSATION
The two key properties we need to describe The two key properties we need to describe are are EVAPORATIONEVAPORATION and its opposite— and its opposite—CONDENSATIONCONDENSATION
break IM bonds
make IM bonds
Add energy
Remove energy
LIQUID VAPOR
<---condensation<---condensation
evaporation--->evaporation--->
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Liquids—Liquids—EvaporationEvaporation
To evaporate, molecules To evaporate, molecules must have sufficient must have sufficient energy to break IM forces.energy to break IM forces.
Breaking IM forces Breaking IM forces requires energy. The requires energy. The process of process of evaporation is evaporation is endothermicendothermic..
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Liquids—Liquids—Distribution of EnergiesDistribution of Energies
Distribution of Distribution of molecular molecular energies in a energies in a liquid.liquid.
KE is propor-KE is propor-tional to T.tional to T.
Distribution of Distribution of molecular molecular energies in a energies in a liquid.liquid.
KE is propor-KE is propor-tional to T.tional to T.
0
Nu
mb
er o
f m
olec
ule
s
Molecular energy
higher Tlower T
See Figure 13.14See Figure 13.14
Minimum energy req’d to break IM forces and evaporate
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Distribution of Energy in a Distribution of Energy in a LiquidLiquid
Figure 13.14
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LiquidsLiquids At higher T a much At higher T a much larger number of larger number of molecules has high molecules has high enough energy to enough energy to break IM forces and break IM forces and move from liquid to move from liquid to vapor state.vapor state.
High E molecules carry High E molecules carry away E. You cool away E. You cool down when sweating down when sweating or after swimming.or after swimming.
.
0
Num
ber
of m
olec
ules
Molecular energy
minimum energy neededto break IM forces and evaporate
higher Tlower T
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LiquidsLiquidsWhen molecules of liquid When molecules of liquid
are in the vapor state, are in the vapor state, they exert a they exert a VAPOR VAPOR PRESSUREPRESSURE
EQUILIBRIUM EQUILIBRIUM VAPOR VAPOR PRESSUREPRESSURE is the is the pressure exerted by a pressure exerted by a vapor over a liquid in a vapor over a liquid in a closed container when closed container when the the rate of evaporation rate of evaporation = the rate of = the rate of condensation.condensation.
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Measuring Equilibrium Measuring Equilibrium Vapor PressureVapor Pressure
Liquid in flask evaporates and exerts pressure on manometer.
Active Fig. 13.17Active Fig. 13.17
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Equilibrium Vapor PressureEquilibrium Vapor PressureActive Figure 13.18Active Figure 13.18
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LiquidsLiquidsEquilibrium Vapor PressureEquilibrium Vapor Pressure
FIGURE 13.18:FIGURE 13.18: VP as a function of T.VP as a function of T.
1. The curves show all conditions of P and 1. The curves show all conditions of P and T where LIQ and VAP are in T where LIQ and VAP are in EQUILIBRIUMEQUILIBRIUM
2. The VP rises with T.2. The VP rises with T.
3. When VP = external P, the liquid boils.3. When VP = external P, the liquid boils.
This means that BP’s of liquids change This means that BP’s of liquids change with altitude.with altitude.
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Boiling LiquidsBoiling Liquids
Liquid boils when its vapor pressure equals atmospheric pressure.
Liquid boils when its vapor pressure equals atmospheric pressure.
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Boiling Point Boiling Point at Lower Pressureat Lower Pressure
When pressure is lowered, the vapor When pressure is lowered, the vapor pressure can equal the external pressure at pressure can equal the external pressure at
a lower temperature.a lower temperature.
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Consequences of Vapor Consequences of Vapor Pressure ChangesPressure Changes
When can cools, vp of water drops. When can cools, vp of water drops. Pressure in the can is less than that of Pressure in the can is less than that of
atmosphere, so can is crushed. atmosphere, so can is crushed.
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4. If external P = 760 mm Hg, T of boiling is the 4. If external P = 760 mm Hg, T of boiling is the
NORMAL BOILING POINTNORMAL BOILING POINT
5. VP of a given molecule at a given T depends 5. VP of a given molecule at a given T depends
on IM forces. Here the VP’s are in the orderon IM forces. Here the VP’s are in the order
C2H5H5C2 HH5C2 HH
wateralcoholether
increasing strength of IM interactions
extensiveH-bondsH-bonds
dipole-dipole
OOO
LiquidsLiquidsFigure 13.18: VP versus TFigure 13.18: VP versus T
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LiquidsLiquids
HEAT OF VAPORIZATIONHEAT OF VAPORIZATION is the heat is the heat req’d (at constant P) to vaporize the liquid.req’d (at constant P) to vaporize the liquid.
LIQ + heat ---> VAPLIQ + heat ---> VAP
Compd.Compd. ∆H∆Hvapvap (kJ/mol) (kJ/mol) IM ForceIM Force
HH22OO 40.7 (100 40.7 (100 ooC)C) H-bondsH-bonds
SOSO22 26.8 (-47 26.8 (-47 ooC)C) dipoledipole
XeXe 12.6 (-107 12.6 (-107 ooC)C) induced induced dipole dipole
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Equilibrium Vapor Pressure Equilibrium Vapor Pressure & the Clausius-Clapeyron & the Clausius-Clapeyron
EquationEquation
• Clausius-Clapeyron equation Clausius-Clapeyron equation
— used to find ∆H˚— used to find ∆H˚vapvap..
• The logarithm of the vapor The logarithm of the vapor
pressure P is proportional to pressure P is proportional to
∆H∆Hvaporiationvaporiation and to 1/T. and to 1/T.
• ln P = –(∆H˚ln P = –(∆H˚vapvap/RT) + C/RT) + C
ln
P2P1
= Hvap
R
1T1
- 1T2
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LiquidsLiquidsMolecules at surface behave differently than those in the interior.Molecules at surface behave differently than those in the interior.
Molecules at surface experience net INWARD Molecules at surface experience net INWARD force of attraction. force of attraction. This leads to This leads to SURFACE TENSIONSURFACE TENSION — the energy — the energy req’d to break the surface.req’d to break the surface.
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Surface TensionSurface Tension
SURFACE TENSIONSURFACE TENSION also leads to spherical also leads to spherical liquid droplets.liquid droplets.
SURFACE TENSIONSURFACE TENSION also leads to spherical also leads to spherical liquid droplets.liquid droplets.
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LiquidsLiquidsIntermolec. forces also lead to Intermolec. forces also lead to CAPILLARYCAPILLARY
action and to the existence of a concave action and to the existence of a concave meniscus for a water column.meniscus for a water column.
concavemeniscus
H2O in
glasstube
ADHESIVE FORCESbetween waterand glass
COHESIVE FORCESbetween watermolecules
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Capillary ActionCapillary Action
Movement of water up a piece of paper Movement of water up a piece of paper depends on H-bonds between Hdepends on H-bonds between H22O and O and the OH groups of the cellulose in the the OH groups of the cellulose in the paper.paper.
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Metallic and Ionic Metallic and Ionic SolidsSolids
Sections 13.6-8Sections 13.6-8
Metallic and Ionic Metallic and Ionic SolidsSolids
Sections 13.6-8Sections 13.6-8
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Types of SolidsTypes of SolidsTable 13.6Table 13.6
TYPETYPE EXAMPLEEXAMPLEFORCEFORCE
Ionic Ionic NaCl, CaFNaCl, CaF22, ZnS, ZnS Ion-ionIon-ion
MetallicMetallic Na, FeNa, Fe MetallicMetallic
MolecularMolecular Ice, IIce, I22 DipoleDipole
Ind. dipoleInd. dipole
NetworkNetwork DiamondDiamond ExtendedExtendedGraphiteGraphite covalentcovalent
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Network SolidsNetwork Solids
A comparison of diamond (pure carbon) A comparison of diamond (pure carbon) with silicon.with silicon.
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Properties of SolidsProperties of Solids
1. Molecules, atoms or 1. Molecules, atoms or ions locked into a ions locked into a
CRYSTAL LATTICECRYSTAL LATTICE2. Particles are CLOSE 2. Particles are CLOSE
togethertogether
3. STRONG IM forces3. STRONG IM forces
4. Highly ordered, rigid, 4. Highly ordered, rigid, incompressibleincompressible
ZnS, zinc sulfideZnS, zinc sulfide
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Crystal LatticesCrystal Lattices• Regular 3-D arrangements of equivalent Regular 3-D arrangements of equivalent
LATTICE POINTS in space.LATTICE POINTS in space.• Lattice points define Lattice points define UNIT CELLSUNIT CELLS
– smallest repeating internal unit that has the symmetry smallest repeating internal unit that has the symmetry characteristic of the solid. characteristic of the solid.
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Cubic Unit CellsCubic Unit Cells
All anglesare 90 degrees
All sidesequal length
There are 7 basic crystal systems, but we are There are 7 basic crystal systems, but we are
only concerned withonly concerned with CUBICCUBIC..
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Cubic Unit Cells of Cubic Unit Cells of MetalsMetalsFigure 13.27Figure 13.27
Simple cubic (SC)Simple cubic (SC) Body-Body-
centered centered cubic (BCC)cubic (BCC)
Face-Face-centered centered cubic (FCC)cubic (FCC)
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Cubic Unit Cells of Cubic Unit Cells of MetalsMetalsFigure 13.27Figure 13.27
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Units Cells for MetalsUnits Cells for Metals
Figure 13.28Figure 13.28
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• E atom is at a corner of a unit cell and is shared among 8 unit cells.
• Each edge is shared with 4 cells• Each face is part of two cells.
Simple Cubic Unit Simple Cubic Unit CellCell
Figure 13.26Figure 13.26
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Atom Packing in Unit Atom Packing in Unit CellsCells
Assume atoms are hard spheres and that crystals are built Assume atoms are hard spheres and that crystals are built by by PACKINGPACKING of these spheres as efficiently as possible. of these spheres as efficiently as possible.
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Atom Packing in Unit Atom Packing in Unit CellsCells
Assume atoms are hard spheres and that crystals are built Assume atoms are hard spheres and that crystals are built by by PACKINGPACKING of these spheres as efficiently as possible. of these spheres as efficiently as possible.
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Crystal Lattices—Crystal Lattices—Packing of Atoms or IonsPacking of Atoms or Ions
• FCC is more efficient FCC is more efficient
than either BC or SC.than either BC or SC.
• Leads to layers of Leads to layers of
atoms.atoms.
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Packing of C60 molecules. They are arranged at the lattice points of a FCC lattice.
Crystal Lattices—Crystal Lattices—Packing of Atoms or IonsPacking of Atoms or Ions
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Number of Atoms per Unit Number of Atoms per Unit CellCell
Unit Cell Type Unit Cell Type Net Number AtomsNet Number Atoms SC SC BCCBCC FCCFCC
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Atom Sharing Atom Sharing at Cube Faces and Cornersat Cube Faces and Corners
Atom shared in corner --> 1/8 inside each unit cell
Atom shared in face --> 1/2 inside each unit cell
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Simple Ionic CompoundsSimple Ionic Compounds
Lattices of many simple ionic solids are built Lattices of many simple ionic solids are built by taking a SC or FCC lattice of ions of one by taking a SC or FCC lattice of ions of one type and placing ions of opposite charge in type and placing ions of opposite charge in the holes in the lattice.the holes in the lattice.
EXAMPLE:EXAMPLE: CsCl has a SC lattice of Cs CsCl has a SC lattice of Cs++ ions ions with Clwith Cl-- in the center. in the center.
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Simple Ionic CompoundsSimple Ionic Compounds
CsCl unit cell has a SC lattice of ClCsCl unit cell has a SC lattice of Cl-- ions with Cs ions with Cs++ in the center. in the center.
1 unit cell has 1 Cs1 unit cell has 1 Cs++ ion ion plusplus
(8 corners)(1/8 Cl(8 corners)(1/8 Cl-- per corner) = 1 net Cl per corner) = 1 net Cl-- ion. ion.
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Two Views of CsCl Unit Two Views of CsCl Unit CellCell
•Lattice can be SC lattice of Cl- with Cs+ in hole•OR SC lattice of Cs+ with Cl- in hole•Either arrangement leads to formula of 1 Cs+ and 1 Cl- per unit cell
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Simple Ionic Simple Ionic CompoundsCompounds
Salts with formula Salts with formula MX can have SC MX can have SC structure — but not structure — but not salts with formula salts with formula MXMX22 or M or M22XX
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NaCl ConstructionNaCl Construction
FCC lattice of Cl- with Na+ in holes
NaNa++ in in octahedral octahedral holesholes
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The Sodium Chloride The Sodium Chloride LatticeLattice
NaNa++ ions are in ions are in OCTAHEDRALOCTAHEDRAL holes holes in a face-centered in a face-centered cubic lattice of Clcubic lattice of Cl-- ions.ions.
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Many common salts have FCC arrangements Many common salts have FCC arrangements of anions with cations in of anions with cations in OCTAHEDRAL OCTAHEDRAL HOLESHOLES — e.g., salts such as CA = NaCl — e.g., salts such as CA = NaCl
•• FCC lattice of anions ----> 4 AFCC lattice of anions ----> 4 A--/unit cell/unit cell
•• CC++ in octahedral holes ---> 1 C in octahedral holes ---> 1 C++ at center at center
+ [12 edges • 1/4 C+ [12 edges • 1/4 C++ per edge] per edge]
= 4 C= 4 C++ per unit cell per unit cell
The Sodium Chloride The Sodium Chloride LatticeLattice
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Comparing NaCl and Comparing NaCl and CsClCsCl
• Even though their formulas have one cation and one anion, the lattices of CsCl and NaCl are different.
• The different lattices arise from the fact that a Cs+ ion is much larger than a Na+ ion.
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Common Ionic SolidsCommon Ionic Solids
Titanium dioxide, Titanium dioxide, TiOTiO22
There are 2 net There are 2 net TiTi4+4+ ions and 4 ions and 4 net Onet O2- 2- ions per ions per unit cell.unit cell.
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Common Ionic SolidsCommon Ionic Solids• Zinc sulfide, ZnSZinc sulfide, ZnS
• The SThe S2-2- ions are in ions are in TETRAHEDRALTETRAHEDRAL holes in the Znholes in the Zn2+2+ FCC lattice.FCC lattice.
• This gives 4 net This gives 4 net ZnZn2+2+ ions and 4 ions and 4 net Snet S2-2- ions. ions.
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Common Ionic Common Ionic SolidsSolids
• Fluorite or CaF2
• FCC lattice of Ca2+ ions
• This gives 4 net Ca2+ ions.
• F- ions in all 8 tetrahedral holes.
• This gives 8 net F- ions.
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Barium titanate, a perovskite
Barium titanate, a perovskite
Ba2+
Ti4+
BaTiO3
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CommoCommon Ionic n Ionic SolidsSolids
Magnesium silicate, Magnesium silicate, MgSiOMgSiO33
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BiotiteBiotiteBiotiteBiotite•Layers of linked octahedra of MgO6 and FeO6.•Layers of linked SiO4 tetrahedra.•K ions between layers
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TRANSITIONS TRANSITIONS BETWEEN BETWEEN PHASESPHASESSection 13.10Section 13.10
Lines connect all conditions of T and P where Lines connect all conditions of T and P where EQUILIBRIUM exists between the phases on either side EQUILIBRIUM exists between the phases on either side of the line.of the line.
(At equilibrium particles move from liquid to gas as fast (At equilibrium particles move from liquid to gas as fast as they move from gas to liquid, for example.)as they move from gas to liquid, for example.)
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Phase Diagram for WaterPhase Diagram for Water
Solid phaseSolid phase
Liquid phaseLiquid phase
Gas phaseGas phase
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Phase Equilibria — WaterPhase Equilibria — WaterSolid-liquidSolid-liquid
Gas-Gas-LiquidLiquid
Gas-Gas-SolidSolid
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Triple Point Triple Point — Water— Water
At the At the TRIPLE POINTTRIPLE POINT all all three phases are in three phases are in equilibrium.equilibrium.
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Phases Phases Diagrams—Diagrams—
Important Points Important Points for Waterfor Water
T(˚C)T(˚C) P(mmHg)P(mmHg)
Normal boil point Normal boil point 100100 760760
Normal freeze pointNormal freeze point 00 760760
Triple point Triple point 0.00980.0098 4.58 4.58
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Critical T and PCritical T and P
.
LIQUID
GAS
Pcritical
Hig
h P
ress
ure
High Temperature
Tcritical
Note that linegoes straight up
Above critical T Above critical T no liquid exists no liquid exists no matter how no matter how high the high the pressure.pressure.
Above critical T Above critical T no liquid exists no liquid exists no matter how no matter how high the high the pressure.pressure.
As P and T increase, you finally reach the As P and T increase, you finally reach the
CRITICAL TCRITICAL T and and PP
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Critical T and PCritical T and PCOMPDCOMPD TTcc((ooC)C) PPcc(atm)(atm)
HH22OO 374374 218218
COCO22 3131 7373
CHCH44 -82-82 4646
Freon-12Freon-12 112112 4141(CCl(CCl22FF22))
Notice that TNotice that Tcc and P and Pcc depend on depend on
intermolecular forces.intermolecular forces.
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Solid-Liquid EquilibriaSolid-Liquid EquilibriaIn any system, if you increase P the In any system, if you increase P the DENSITYDENSITY will go will go
up. up.
Therefore — as P goes up, equilibrium favors phase Therefore — as P goes up, equilibrium favors phase
with the larger density (or with the larger density (or SMALLERSMALLER volume/gram).volume/gram).
Liquid HLiquid H22OOSolid HSolid H22OO
DensityDensity 1 g/cm1 g/cm33 0.917 g/cm0.917 g/cm33
cmcm33/gram/gram 11 1.091.09
LIQUID H2OICEfavored atlow P
favored athigh P
LIQUID H2OICEfavored atlow P
favored athigh P
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Solid-Liquid EquilibriaSolid-Liquid Equilibria
Raising the pressure at Raising the pressure at constant T causes constant T causes water to melt.water to melt.
The NEGATIVE SLOPE The NEGATIVE SLOPE of the S/L line is of the S/L line is unique to Hunique to H22O. O.
Almost everything Almost everything else has positive else has positive slope.slope.
SolidH2O
LiquidH2O
P
T
760mmHg
0 ÞC
Normalfreezingpoint
LIQUID H2OICEfavored atlow P
favored athigh P
LIQUID H2OICEfavored atlow P
favored athigh P
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Solid-Solid-Liquid Liquid
EquilibriaEquilibria
The behavior of water The behavior of water under pressure is an under pressure is an example of example of
LE CHATELIER’S LE CHATELIER’S PRINCIPLEPRINCIPLE
At Solid/Liquid At Solid/Liquid equilibrium, raising P equilibrium, raising P squeezes the solid. squeezes the solid.
It responds by going to It responds by going to phase with greater phase with greater density, i.e., the liquid density, i.e., the liquid phase.phase.
SolidH2O
LiquidH2O
P
T
760mmHg
0 ÞC
Normalfreezingpoint
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Solid-Vapor EquilibriaSolid-Vapor EquilibriaAt P < 4.58 mmHg and T < 0.0098 ˚CAt P < 4.58 mmHg and T < 0.0098 ˚C
solid Hsolid H22O can go directly to vapor. This O can go directly to vapor. This
process is called process is called SUBLIMATIONSUBLIMATION
This is how a frost-free refrigerator works.This is how a frost-free refrigerator works.