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CHAPTER 13 –
• LIQUIDS AND SOLIDS
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WHY?WHY?• 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 Cl2is a gas?
• Why are NaCl crystals little cubes?
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Inter-molecular Forces
InterInter--molecular molecular ForcesForces
Have studied Have studied INTRAmolecularINTRAmolecular forcesforces——the forces holding atoms together to the forces holding atoms together to form molecules.form molecules.
Now turn to forces between molecules Now turn to forces between molecules ——INTERmolecularINTERmolecular forces. forces.
Forces between molecules, between ions, Forces between molecules, between ions, or between molecules and ions.or between molecules and ions.
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Kinetic-Molecular Description of Liquids and Solids•• Solids and liquids are Solids and liquids are condensed states.condensed states.
–– The atoms, ions, or molecules in solids and The atoms, ions, or molecules in solids and liquids are much closer to one another than liquids are much closer to one another than in gases.in gases.
•• Liquids and gases are Liquids and gases are fluids.fluids.
• The intermolecular attractionsintermolecular attractions in in liquids and solids are strong.liquids and solids are strong.
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Liquids and Solids
•• Strengths of interactionsStrengths of interactions among particles
Gases< Liquids < Solids
•• Miscible liquidsMiscible liquids are soluble (dissolve) in each other.
• Water dissolves in alcohol.
••Immiscible liquidsImmiscible liquids are insoluble in each other.
•Water does not dissolve in oil.
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Intermolecular Attractions – 4 Important
1. Ion-ion interactions – Strongest IM Force– The force of attraction between two
oppositely charged ions is governed by Coulomb’s law.
( )( )
ions. ebetween th distance theis d
charges.ion theare q and q
d
qqF
-
2
-
+
+
∝
•Coulomb’s law determines:
1.The melting and boiling points of ionic compounds.
2.The solubility of ionic compounds.
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Ion-Ion Forcesfor comparison of magnitudeIonIon--Ion ForcesIon Forcesfor comparison of magnitudefor comparison of magnitude
NaNa++——ClCl-- in saltin salt
These are the strongest These are the strongest forces. forces.
Lead to solids with high Lead to solids with high melting temperatures.melting temperatures.
NaClNaCl, mp = 800 , mp = 800 ooCC
MgOMgO, mp = 2800 , mp = 2800 ooCC
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Covalent Bonding Forcesfor comparison of magnitudeCovalent Bonding ForcesCovalent Bonding Forcesfor comparison of magnitudefor comparison of magnitude
CC––H, 413 kJ/molH, 413 kJ/mol
C=C, 610 kJ/molC=C, 610 kJ/mol
CC––C, 346 kJ/molC, 346 kJ/mol
CN, 887 kJ/molCN, 887 kJ/mol
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Attraction Between Ions and Permanent DipolesAttraction Between Ions Attraction Between Ions and Permanent Dipolesand Permanent Dipoles
Water is highly polar and Water is highly polar and can interact with positive can interact with positive ions to give ions to give hydrated hydrated ions in water.ions in water.
H
H
water dipole
••
••
O-δδδδ
+δδδδ
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Attraction Between Ions and Permanent DipolesAttraction Between Ions Attraction Between Ions and Permanent Dipolesand Permanent Dipoles
Water is highly polar and Water is highly polar and can interact with positive can interact with positive ions to give ions to give hydrated hydrated ions in water.ions in water.
H
H
water dipole
••
••
O-δδδδ
+δδδδ
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Attraction Between Ions and Permanent DipolesAttraction Between Ions Attraction Between Ions and Permanent Dipolesand Permanent Dipoles
Many metal ions are hydrated. Many metal ions are hydrated. This is the reason metal salts This is the reason metal salts dissolve in water.dissolve in water.
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Attraction between ions and dipole depends on ionAttraction between ions and dipole depends on ioncharge and ioncharge and ion--dipole distance.dipole distance.
Measured by Measured by ∆∆H for H for MMnn++ + H+ H22O O ----> [M(H> [M(H22O)O)xx]]n+n+
--1922 kJ/mol1922 kJ/mol --405 kJ/mol405 kJ/mol --263 kJ/mol263 kJ/mol
Attraction Between Ions and Permanent DipolesAttraction Between Ions and Attraction Between Ions and Permanent DipolesPermanent Dipoles
OH
Hδδδδ+
δδδδ-• • • O
H
Hδδδδ+
δδδδ-• • • O
H
Hδδδδ+
δδδδ-• • •
Na+Mg
2+
Cs+
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Intermolecular Attractions and Phase Changes
3. 3. Dipole-dipole interactions– Consider CO2 vs. NO2
– CO2 – MP –78 ºC
– NO2 – MP 21 ºC
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Dipole-Dipole ForcesDipoleDipole--Dipole ForcesDipole Forces
Such forces bind molecules having Such forces bind molecules having permanent dipoles to one permanent dipoles to one another.another.
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Dipole-Dipole ForcesDipoleDipole--Dipole ForcesDipole Forces
Influence of dipoleInfluence of dipole--dipole forces is seen in the dipole forces is seen in the boiling points of simple molecules.boiling points of simple molecules.
CompdCompd Mol. Wt.Mol. Wt. Boil PointBoil Point
NN22 2828 --196 196 ooCC
COCO 2828 --192 192 ooCC
BrBr22 160160 59 59 ooCC
IClICl 162162 97 97 ooCC
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Intermolecular Attractions
2. 4. Hydrogen bonding – IM Force between dipole induced by H and N, O, F only
– H2O - very polar molecule.
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Hydrogen BondingHydrogen BondingHydrogen Bonding
A special form of dipoleA special form of dipole--dipole attraction, dipole attraction, which enhances dipolewhich enhances dipole--dipole attractions.dipole attractions.
HH--bonding is strongest when X and Y are bonding is strongest when X and Y are N, O, or FN, O, or F
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H-Bonding Between Methanol and WaterHH--Bonding Between Methanol Bonding Between Methanol and Waterand Water
H-bondHH--bondbond--δδδδδδδδ
++δδδδδδδδ
--δδδδδδδδ
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H-Bonding Between Two Methanol MoleculesHH--Bonding Between Two Bonding Between Two Methanol MoleculesMethanol Molecules
H-bondHH--bondbond
--δδδδδδδδ
++δδδδδδδδ
--δδδδδδδδ
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H-Bonding Between Ammonia and WaterHH--Bonding Between Ammonia Bonding Between Ammonia and Waterand Water
H-bondHH--bondbond
--δδδδδδδδ
++δδδδδδδδ --δδδδδδδδ
This HThis H--bond leads to the formation of bond leads to the formation of
NHNH44++ and OHand OH--
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Hydrogen Bonding in H2OHydrogen Bonding in HHydrogen Bonding in H22OO
HH--bonding is especially bonding is especially strong in water strong in water becausebecause
•• the Othe O——H bond is very 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 waterwater’’s unique s unique properties.properties.
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Hydrogen Bonding in H2OHydrogen Bonding in HHydrogen Bonding in H22OO
Ice has open Ice has open latticelattice--like like structure.structure.
Ice density is Ice density is < liquid.< liquid.
And so solid And so solid floats on floats on water.water.
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Hydrogen Bonding in H2OHydrogen Bonding in HHydrogen Bonding in H22OO
Ice has open latticeIce has open lattice--like structure.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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Boiling Points of Simple Boiling Points of Simple HydrogenHydrogen--Containing Containing CompoundsCompounds
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Intermolecular Attractions
4. 5. London Forces are very weak.– Only attractive force in nonpolar molecules.
– Induced dipole-Induced dipole interactions
• Consider I2 as an isolated molecule.
• I2 – MP 110 ºC
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FORCES INVOLVING INDUCED DIPOLESFORCES INVOLVING FORCES INVOLVING INDUCED DIPOLESINDUCED DIPOLES
How can nonHow can non--polar molecules such as Opolar molecules such as O2 2 and and II22 dissolve in water?dissolve in water?
The water dipole The water dipole INDUCESINDUCES a dipole in a dipole in
the Othe O22 electric cloud. electric cloud.
Dipole-induced
dipole
DipoleDipole--induced induced
dipoledipole
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FORCES INVOLVING INDUCED DIPOLESFORCES INVOLVING FORCES INVOLVING INDUCED DIPOLESINDUCED DIPOLES
Solubility increases with mass the gasSolubility increases with mass the gas
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FORCES INVOLVING INDUCED DIPOLESFORCES INVOLVING FORCES INVOLVING INDUCED DIPOLESINDUCED DIPOLES
•• Process of inducing a dipole is Process of inducing a dipole is polarizationpolarization
•• Degree to which electron cloud Degree to which electron cloud of an atom or molecule can be of an atom or molecule can be distorted in its distorted in its polarizabilitypolarizability..
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IM FORCES — INDUCED DIPOLESIM FORCES IM FORCES —— INDUCED DIPOLESINDUCED DIPOLES
Consider IConsider I22
dissolving dissolving in ethanol, in ethanol, CHCH33CHCH22OH.OH.
OH
-δδδδ
+δδδδ
I-I
R
-δδδδ
+δδδδ
OH+δδδδ
-δδδδ
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 INDUCED DIPOLESFORCES INVOLVING FORCES INVOLVING INDUCED DIPOLESINDUCED DIPOLES
Formation of a dipole in two Formation of a dipole in two nonpolarnonpolar II22
molecules.molecules.
Induced dipole-
induced dipole
Induced dipoleInduced dipole--
induced dipoleinduced dipole
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FORCES INVOLVING INDUCED DIPOLESFORCES INVOLVING FORCES INVOLVING INDUCED DIPOLESINDUCED DIPOLES
The induced forces between IThe induced forces between I22
molecules are very weak, so solid Imolecules are very weak, so solid I22
sublimessublimes (goes from a solid to (goes from a solid to
gaseous molecules).gaseous molecules).
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FORCES INVOLVING INDUCED DIPOLESFORCES INVOLVING FORCES INVOLVING INDUCED DIPOLESINDUCED DIPOLES
The magnitude of the induced dipole depends on The magnitude of the induced dipole depends on the tendency to be distorted. the tendency to be distorted.
Higher Higher molecmolec. weight . weight ------> larger induced > larger induced dipoles.dipoles.
MoleculeMolecule Boiling Point Boiling Point ((ooCC))
CHCH44 (methane) (methane) -- 161.5161.5
CC22HH66 (ethane)(ethane) -- 88.6 88.6
CC33HH88 (propane) (propane) -- 42.142.1
CC44HH1010 (butane) (butane) -- 0.50.5
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Boiling Points of HydrocarbonsBoiling Points of Hydrocarbons
Note linear relation between bp and molar mass.
CHCH44
CC22HH66
CC33HH88
CC44HH1010
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Intermolecular Forces SummaryIntermolecular Forces Summary
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LiquidsLiquidsLiquidsIn a liquidIn a liquid
•• molecules are in constant molecules are in constant motionmotion
•• there are appreciable there are appreciable intermolecintermolec. forces. forces
•• molecules close togethermolecules close together
•• 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 are EVAPORATION and its opposite—CONDENSATION
The two key properties we need to The two key properties we need to describe are EVAPORATION and its describe are EVAPORATION and its oppositeopposite——CONDENSATIONCONDENSATION
break IM bonds
make IM bonds
Add energy
Remove energy
LIQUID VAPOR
<<------condensationcondensation
evaporationevaporation------>>
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LiquidsLiquids——EvaporationEvaporation
To evaporate, To evaporate, molecules must molecules must have sufficient have sufficient energy to break energy to break IM forces.IM forces.
Breaking IM forces Breaking IM forces
requires energy. The requires energy. The
process of process of
evaporation is evaporation is
endothermic.endothermic.
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LiquidsLiquids——Distribution of EnergiesDistribution of Energies
Distribution of molecular energies in a liquid.
KE is propor-tional to T.
Distribution of Distribution of molecular molecular energies in energies in a liquid.a liquid.
KE is KE is proporpropor--tionaltional to T.to T.0
Number of molecules
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 LiquidDistribution of Energy in a Liquid
•Molecules escape from the surface of a liquid and
•become a gas - temperature dependent.
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The Liquid State - Vapor Pressure
• Pressure exerted by a liquid’s vapor on its surface at equilibrium.
• Vapor Pressure (torr) and boiling point for three liquids at different temperatures.
0 oC 20 oC 30 oC normal boiling point
diethyl ether 185 442 647 36oCethanol 12 44 74 78oC
water 5 18 32 100oC
Boiling Point – Temperature at which VP = Atm. Pressure
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LiquidsLiquidsWhen molecules of liquid are in When molecules of liquid are in
the vapor state, they exert a the vapor state, they exert a VAPOR PRESSUREVAPOR PRESSURE
EQUILIBRIUM VAPOR EQUILIBRIUM VAPOR PRESSUREPRESSURE is the pressure is the pressure exerted by a vapor over a exerted by a vapor over a liquid in a closed container liquid in a closed container when the when the rate of evaporation rate of evaporation = the rate of condensation.= the rate of condensation.
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Measuring Equilibrium Measuring Equilibrium Vapor PressureVapor Pressure
Liquid in flask evaporates and exerts pressure on manometer.
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LiquidsLiquids
HEAT OF VAPORIZATIONHEAT OF VAPORIZATION is the heat is the heat reqreq’’dd (at (at constant P) to vaporize the liquid.constant P) to vaporize the liquid.
LIQ + heat LIQ + heat ------> VAP> VAP
Compd.Compd. ∆∆HHvapvap (kJ/mol) (kJ/mol) IM ForceIM Force
HH22OO 40.7 (100 40.7 (100 ooCC)) HH--bondsbonds
SOSO22 26.8 (26.8 (--47 47 ooCC)) dipoledipole
XeXe 12.6 (12.6 (--107 107 ooCC)) induced dipole induced dipole
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The Liquid State – Energy and Phase Change
• Heat of Vaporization - amount of heat required to change 1.00 g of a liquid substance to a gas at constant temperature (units of J/g).
• Heat of Condensation is the reverse of heat of vaporization, phase change from gas to liquid.
← →+
J 2260-
o
(g)2
J 2260o
)(2 C100.0at OH g 00.1C100.0at OH g 1.00l
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The Liquid State
Molar heat of vaporization or ∆∆∆∆Hvap
• Heat required to change 1.00 mole of a liquid to a gas at constant temperature.
∆Hvap has units of J/mol.
Molar heat of condensation• The reverse of molar heat of vaporization is the heat of condensation.
← →+
kJ 40.7-
o
(g)2
kJ 40.7o
)(2 C100.0at OH mol 00.1C100.0at OH mol 1.00l
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Equilibrium Vapor Pressure & the Equilibrium Vapor Pressure & the ClausiusClausius--ClapeyronClapeyron EquationEquation
•• ClausiusClausius--ClapeyronClapeyron equation equation
—— used to find used to find ∆∆HH˚̊vapvap..
•• The logarithm of the vapor The logarithm of the vapor
pressure P is proportional to pressure P is proportional to
∆∆HHvaporiationvaporiation and to 1/T.and to 1/T.
•• lnln P = P = ––((∆∆HH˚̊vapvap/RT) + C/RT) + C
lnP2P1
= ∆HvapR
1
T1 -
1
T2
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The Liquid State
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The Liquid State - Heat Transfer
q = m C T∆
•Example: How much heat is released by 225 g of H2O as it cools from 85.0
oC to
40.0 oC? The specific heat of water is
4.184 J/goC.
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The Liquid State• Example: How many joules of energy must
be absorbed by 5.00 x 102 g of H2O at 50.0oC to convert it to steam at 120oC? The molar heat of vaporization of water is 40.7 kJ/mol and the molar heat capacities of liquid water and steam are 75.3 J/mol oCand 36.4 J/mol oC, respectively.
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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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The Liquid State
• Boiling Points of Various Kinds of Liquids
Gas MW BP(oC)He 4 -269
Ne 20 -246
Ar 40 -186
Kr 84 -153
Xe 131 -107
Rn 222 -62
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The Liquid State
Compound MW(amu) B.P.(oC)
CH4 16 -161
C2H6 30 -88
C3H8 44 -42
n-C4H10 58 -0.6
n-C5H12 72 +36
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The Liquid State - ViscosityViscosity
• Viscosity is the resistance to flow.– For example, compare how water pours
out of a glass compared to molasses, syrup or honey.
• Oil for your car is bought based on this property.– 10W30 or 5W30 describes the viscosity of
the oil at high and low temperatures.
– Greater IM Force � Greater viscosity
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The Liquid State - Surface TensionSurface Tension
• Molecules at the surface are attracted unevenly.
• Measure of inward forces that must be overcome to expand the molecules at the surface.
• Consider water – surface vs submerged
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LiquidsLiquids
Molecules at surface behave differently than those Molecules at surface behave differently than those in the interior.in the interior.
Molecules at surface experience net INWARD Molecules at surface experience net INWARD
force of attraction. force of attraction.
This leads to SURFACE TENSION This leads to SURFACE TENSION —— the energy the energy
reqreq’’dd to break the surface.to break the surface.
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The Liquid State
• Cohesive forces are the forces that hold liquids together.
• Adhesive forces are the forces between a liquid and another surface.– Capillary rise implies that the:
• Adhesive forces > cohesive forces
– Capillary fall implies that the:• Cohesive forces > adhesive forces
• affects the meniscus of liquidsWater
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LiquidsLiquidsIntermolecIntermolec. forces also lead to CAPILLARY action . forces also lead to CAPILLARY action
and to the existence of a concave meniscus for a and to the existence of a concave meniscus for a water column.water column.
concave
meniscus
H2O in
glass
tube
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 Hdepends on H--bonds between Hbonds 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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The Solid State - Normal Melting Point
• Temperature at which the solid melts (liquid and solid in equilibrium) at exactly 1.00 atm of pressure.
• MP increases as IM Forces increase.
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The Solid State
• Which requires more energy?
( ) ( )
( ) ( )←→
←→
l
l
OHOH
or
NaClNaCl
2s2
s
� What experimental proof do you have?
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Heat Transfer Involving Solids
Heat of fusionHeat of fusion - heat required to melt one gram of a solid at its melting point
at constant temperature.
•• Heat of crystallization Heat of crystallization is the reverse of
the heat of fusion.
← →+
J 334-
o
)(2
J 334 o
(s)2 C0at OH g 1.00 C0at OH g 1.00l
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Heat Transfer Involving Solids
Molar heat of fusion or ∆∆∆∆Hfusion• The molar heat of fusion per mole of a
substance at its melting point.
• The molar heat of crystallization is thereverse of molar heat of fusion
← →+
J 6012-
o
)(2
J 6012o
(s)2 C0at OH mole 1.00 C0at OH mole 1.00l
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Heat Transfer Involving Solids
• Example: Calculate the amount of heat required to convert 150.0 g of ice at
• -10.0oC to water at 40.0oC.specific heat of ice is 2.09 J/goC
Heat of fusion – 334 J/g
Specific heat of water 4.18 J/goC
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Sublimation
• Solid transforms directly to the vapor phase
• Solid CO2 or “dry” ice does this well.
← →oncondensati
nsublimatio
gas solid
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Phase DiagramsPhase Diagrams
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TRANSITIONS TRANSITIONS BETWEEN PHASESBETWEEN PHASESSection 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 EQUILIBRIUM exists between the phases on either side of the line.either side of the line.
(At equilibrium particles move from liquid to (At equilibrium particles move from liquid to gas as fast as they move from gas to liquid, gas as fast as they move from gas to liquid, for example.)for example.)
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Critical T and PCritical T and P
.
LIQUID
GAS
Pcritical
High Pressure
High Temperature
Tcritical
Note that linegoes straight up
Above critical T
no liquid exists
no matter how
high the
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 As P and T increase, you finally
reach the reach the CRITICAL TCRITICAL T and and PP
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Phase Diagrams (P versus T)• Display the different phase transitions of a
substance - water.
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Triple Point Triple Point ——WaterWater
At the At the TRIPLE POINT TRIPLE POINT all all
three phases are in three phases are in
equilibrium.equilibrium.
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Phases Phases DiagramsDiagrams——Important Points for Important Points for WaterWater
T(T(˚̊C)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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COCO22 Phase DiagramPhase Diagram
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Critical T and PCritical T and P
COMPDCOMPD TTcc((ooCC)) PPcc(atm(atm))
HH22OO 374374 218218
COCO22 3131 7373
CHCH44 --8282 4646
FreonFreon--1212 112112 4141(CCl(CCl22FF22))
Notice that Notice that TTcc and Pand Pcc depend on depend on intermolecular forces.intermolecular forces.