Post on 29-Dec-2015
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CHAPTER 9CHAPTER 9
Liquids and SolidsLiquids and Solids
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Description of Liquids & SolidsDescription of Liquids & Solids• Solids & liquids are Solids & liquids are condensed statescondensed states
• atoms, ions, molecules are close to one anotheratoms, ions, molecules are close to one another• highly incompressiblehighly incompressible• Solid molecules are packed closely together. The molecules are Solid molecules are packed closely together. The molecules are
so rigidly packed that they cannot easily slide past each other.so rigidly packed that they cannot easily slide past each other.
• Liquids & gases are Liquids & gases are fluidsfluids• easily floweasily flow• Liquids molecules are held closer together than gas molecules, Liquids molecules are held closer together than gas molecules,
but not so rigidly that the molecules cannot slide past each but not so rigidly that the molecules cannot slide past each other.other.
• Intermolecular attractionsIntermolecular attractions in liquids & solids are strongin liquids & solids are strong
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Description of Liquids & Solids
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Converting a gas into a liquid or solid requires Converting a gas into a liquid or solid requires the molecules to get closer to each other:the molecules to get closer to each other: cool or compress.cool or compress.
Converting a solid into a liquid or gas requires Converting a solid into a liquid or gas requires the molecules to move further apart: the molecules to move further apart: heat or reduce pressure.heat or reduce pressure.
The forces holding solids and liquids together The forces holding solids and liquids together are called are called intermolecular forces.intermolecular forces.
Description of Liquids & Solids
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Kinetic-Molecular Description of Kinetic-Molecular Description of Liquids & SolidsLiquids & Solids
strengths of interactionsstrengths of interactions among particles & among particles & degree of orderingdegree of ordering of particles of particles
Gases< Liquids < SolidsGases< Liquids < Solids
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Intermolecular Attractions
The covalent bond holding a molecule together is an The covalent bond holding a molecule together is an intramolecular forces.intramolecular forces.
The attraction between molecules is an intermolecular The attraction between molecules is an intermolecular force.force.
Intermolecular forces are much weaker than intramolecular Intermolecular forces are much weaker than intramolecular forces (e.g. 16 kJ/mol vs. 431 kJ/mol for HCl).forces (e.g. 16 kJ/mol vs. 431 kJ/mol for HCl).
When a substance melts or boils the intermolecular forces When a substance melts or boils the intermolecular forces are broken (not the covalent bonds).are broken (not the covalent bonds).
When a substance condenses intermolecular forces are When a substance condenses intermolecular forces are
formedformed..
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Intermolecular Attractions
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Intermolecular AttractionsDipole-Dipole ForcesDipole-Dipole Forces Dipole-dipole forces exist between neutral Dipole-dipole forces exist between neutral
polar molecules.polar molecules. Polar molecules need to be close together.Polar molecules need to be close together. Weaker than ion-dipole forces:Weaker than ion-dipole forces:
QQ11 and and QQ22 are are partialpartial charges. charges.
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d
QQkF
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Intermolecular Attractions
Dipole-Dipole ForcesDipole-Dipole Forces There is a mix of attractive and There is a mix of attractive and
repulsive dipole-dipole forces repulsive dipole-dipole forces as the molecules tumble.as the molecules tumble.
If two molecules have about If two molecules have about the same mass and size, then the same mass and size, then dipole-dipole forces increase dipole-dipole forces increase with increasing polarity.with increasing polarity.
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Intermolecular AttractionsIntermolecular Attractions
Dipole-dipole interactionsDipole-dipole interactions consider NHconsider NH33 a very polar molecule a very polar molecule
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Intermolecular Attractions
Dispersion Forces Weakest of all intermolecular forces.Weakest of all intermolecular forces. It is possible for two adjacent neutral molecules to It is possible for two adjacent neutral molecules to
affect each other.affect each other. The nucleus of one molecule (or atom) attracts the The nucleus of one molecule (or atom) attracts the
electrons of the adjacent molecule (or atom).electrons of the adjacent molecule (or atom). For an instant, the electron clouds become For an instant, the electron clouds become
distorted.distorted. In that instant a dipole is formed (called an In that instant a dipole is formed (called an
instantaneous dipole).instantaneous dipole).
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Intermolecular AttractionsDispersion Forces
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Polarizability is the ease with which an Polarizability is the ease with which an electron cloud can be deformed.electron cloud can be deformed.
The larger the molecule (the greater the The larger the molecule (the greater the number of electrons) the more number of electrons) the more polarizable.polarizable.
Intermolecular Attractions
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Intermolecular Attractions
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Intermolecular AttractionsDispersion Forces London dispersion forces depend on the London dispersion forces depend on the
shape of the molecule.shape of the molecule. The greater the surface area available for The greater the surface area available for
contact, the greater the dispersion forces.contact, the greater the dispersion forces. London dispersion forces between London dispersion forces between
spherical molecules are lower than spherical molecules are lower than between sausage-like molecules.between sausage-like molecules.
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Intermolecular AttractionsIntermolecular Attractions
Hydrogen bondingHydrogen bonding consider Hconsider H22OO
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Hydrogen BondingHydrogen Bonding Special case of dipole-dipole forces.Special case of dipole-dipole forces. By experiments: boiling points of By experiments: boiling points of
compounds with H-F, H-O, and H-N compounds with H-F, H-O, and H-N bonds are abnormally high.bonds are abnormally high.
Intermolecular forces are abnormally Intermolecular forces are abnormally strong.strong.
Intermolecular Attractions
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Hydrogen BondingHydrogen Bonding H-bonding requires H bonded to an H-bonding requires H bonded to an
electronegative element (most important electronegative element (most important for compounds of F, O, and N).for compounds of F, O, and N). Electrons in the H-X (X = electronegative Electrons in the H-X (X = electronegative
element) lie much closer to X than H.element) lie much closer to X than H. H has only one electron, so in the H-X H has only one electron, so in the H-X
bond, the bond, the + H presents an almost bare + H presents an almost bare proton to the proton to the - X.- X.
Therefore, H-bonds are strong.Therefore, H-bonds are strong.
Intermolecular Attractions
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Hydrogen BondingHydrogen BondingIntermolecular Attractions
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Hydrogen BondingHydrogen Bonding Ice FloatingIce Floating
• Solids are usually more closely packed than liquids;Solids are usually more closely packed than liquids;• therefore, solids are more dense than liquids.therefore, solids are more dense than liquids.• Ice is ordered with an open structure to optimize H-bonding.Ice is ordered with an open structure to optimize H-bonding.• Therefore, ice is less dense than water.Therefore, ice is less dense than water.• In water the H-O bond length is 1.0 Å.In water the H-O bond length is 1.0 Å.• The O…H hydrogen bond length is 1.8 Å.The O…H hydrogen bond length is 1.8 Å.• Ice has waters arranged in an open, regular hexagon.Ice has waters arranged in an open, regular hexagon.• Each Each + H points towards a lone pair on O.+ H points towards a lone pair on O.• Ice floats, so it forms an insulating layer on top of lakes, Ice floats, so it forms an insulating layer on top of lakes,
rivers, etc. Therefore, aquatic life can survive in winter.rivers, etc. Therefore, aquatic life can survive in winter.
Intermolecular Attractions
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Hydrogen BondingHydrogen Bonding Hydrogen bonds Hydrogen bonds
are responsible for:are responsible for: Protein StructureProtein Structure
• Protein folding is a Protein folding is a consequence of H-consequence of H-bonding.bonding.
• DNA Transport of DNA Transport of Genetic InformationGenetic Information
Intermolecular Attractions
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Comparing Intermolecular Attractions
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Intermolecular AttractionsIntermolecular Attractions
Coulomb’s law & the attraction energy Coulomb’s law & the attraction energy determine: determine: melting & boiling points of ionic compoundsmelting & boiling points of ionic compounds the solubility of ionic compoundsthe solubility of ionic compounds
Arrange the following ionic compounds Arrange the following ionic compounds in the expected order of increasing in the expected order of increasing melting and boiling points.melting and boiling points.
NaF, CaO, CaFNaF, CaO, CaF22
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Intermolecular Attractions and Intermolecular Attractions and Phase ChangesPhase Changes
Na F Ca F Ca O+ - 2+2
2+ 2-
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Intermolecular Attractions and Intermolecular Attractions and Phase ChangesPhase Changes
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EvaporationEvaporation
Process in which molecules escape from Process in which molecules escape from the surface of a liquidthe surface of a liquid T dependentT dependent
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EvaporationEvaporation
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Vapor PressureVapor Pressure
pressure exerted by a liquid’s vapor on its pressure exerted by a liquid’s vapor on its surface at equilibriumsurface at equilibrium
Vap. Press. (torr) for 3 LiquidsVap. Press. (torr) for 3 Liquids Norm. Norm. B.P.B.P.
00ooCC 20 20ooCC 30 30ooCC diethyl etherdiethyl ether 185 185 442 442 647 647 3636ooCC ethanolethanol 12 12 44 44 74 74 7878ooCC waterwater 5 5 18 18 32 32 100100ooCC
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Vapor PressureVapor Pressure
Some of the molecules on the surface of a liquid Some of the molecules on the surface of a liquid have enough energy to escape the attraction of have enough energy to escape the attraction of the bulk liquid.the bulk liquid.
These molecules move into the gas phase.These molecules move into the gas phase. As the number of molecules in the gas phase As the number of molecules in the gas phase
increases, some of the gas phase molecules increases, some of the gas phase molecules strike the surface and return to the liquid.strike the surface and return to the liquid.
After some time the pressure of the gas will be After some time the pressure of the gas will be constant at the vapor pressure.constant at the vapor pressure.
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Dynamic Equilibrium: the Dynamic Equilibrium: the point when as many point when as many molecules escape the molecules escape the surface as strike the surface as strike the surface.surface.
Vapor pressure is the Vapor pressure is the pressure exerted when the pressure exerted when the liquid and vapor are in liquid and vapor are in dynamic equilibrium.dynamic equilibrium.
Vapor PressureVapor Pressure
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If equilibrium is never established then If equilibrium is never established then the liquid evaporates.the liquid evaporates.
Volatile substances evaporate rapidly.Volatile substances evaporate rapidly. The higher the temperature, the higher The higher the temperature, the higher
the average kinetic energy, the faster the the average kinetic energy, the faster the liquid evaporates.liquid evaporates.
Vapor PressureVapor Pressure
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Liquids boil when the external pressure equals Liquids boil when the external pressure equals the vapor pressure.the vapor pressure.
Temperature of boiling point increases as Temperature of boiling point increases as pressure increases.pressure increases.
Two ways to get a liquid to boil: increase Two ways to get a liquid to boil: increase temperature or decrease pressure.temperature or decrease pressure. Pressure cookers operate at high pressure. At high Pressure cookers operate at high pressure. At high
pressure the boiling point of water is higher than at 1 pressure the boiling point of water is higher than at 1 atm. Therefore, there is a higher temperature at atm. Therefore, there is a higher temperature at which the food is cooked, reducing the cooking time which the food is cooked, reducing the cooking time required.required.
Vapor PressureVapor Pressure
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Boiling PointsBoiling Points
Boiling point is temperature at which the Boiling point is temperature at which the liquid’s vapor pressure is equal to applied liquid’s vapor pressure is equal to applied pressurepressure normal boiling point is boiling point @ 1 atmnormal boiling point is boiling point @ 1 atm
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DistillationDistillation
Process in which a mixture or solution is Process in which a mixture or solution is separated into its components on the separated into its components on the basis of the differences in boiling points of basis of the differences in boiling points of the componentsthe components Distillation is another vapor pressure Distillation is another vapor pressure
phenomenon.phenomenon.
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The Liquid StateThe Liquid State energy associated with changes of stateenergy associated with changes of state
heat of vaporizationheat of vaporizationamount of heat required to change 1 g of amount of heat required to change 1 g of a liquid substance to a gas at a liquid substance to a gas at constant Tconstant Tunits of J/gunits of J/g
heat of condensationheat of condensationreverse of heat of vaporizationreverse of heat of vaporization
1.00 g H O @ 100 C 1.00 g H O @ 100 C2 (l)o
-2260 J
+2260 J
2 (g)o
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The Liquid StateThe Liquid State
molar heat of vaporization or molar heat of vaporization or HHvapvap
amount of heat required to change 1 mol of amount of heat required to change 1 mol of a liquid to a gas at a liquid to a gas at constant Tconstant T
units of J/mol units of J/mol
molar heat of condensationmolar heat of condensation
reverse of molar heat of vaporizationreverse of molar heat of vaporization
1.00 mol H O @ 100 C 1.00 mol H O @ 100 C2 (l)o
-40.7 kJ
+40.7 kJ
2 (g)o
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The Liquid StateThe Liquid State
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Surface molecules are only attracted Surface molecules are only attracted inwards towards the bulk molecules.inwards towards the bulk molecules.
SublimationSublimation: solid : solid gas. gas. VaporizationVaporization: liquid : liquid gas. gas. Melting Melting or or fusionfusion: solid : solid liquid. liquid. DepositionDeposition: gas : gas solid. solid. CondensationCondensation: gas : gas liquid. liquid. FreezingFreezing: liquid : liquid solid. solid.
Phase ChangesPhase Changes
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SublimationSublimation: : HHsubsub > 0 (endothermic). > 0 (endothermic).
VaporizationVaporization: : HHvapvap > 0 (endothermic). > 0 (endothermic).
Melting Melting or or FusionFusion: : HHfusfus > 0 (endothermic). > 0 (endothermic).
DepositionDeposition: : HHdepdep < 0 (exothermic). < 0 (exothermic).
CondensationCondensation: : HHconcon < 0 (exothermic). < 0 (exothermic).
FreezingFreezing: : HHfrefre < 0 (exothermic). < 0 (exothermic).
Generally heat of fusion (enthalpy of fusion) is Generally heat of fusion (enthalpy of fusion) is less than heat of vaporization:less than heat of vaporization: it takes more energy to completely separate it takes more energy to completely separate
molecules, than partially separate them.molecules, than partially separate them.
Phase ChangesPhase Changes
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All phase changes are possible under the right All phase changes are possible under the right conditions (e.g. water sublimes when snow conditions (e.g. water sublimes when snow disappears without forming puddles).disappears without forming puddles).
The sequenceThe sequence
heat solid heat solid melt melt heat liquid heat liquid boil boil heat gas heat gas
is is endothermicendothermic.. The sequence The sequence
cool gas cool gas condense condense cool liquid cool liquid freeze freeze
cool solidcool solid
is is exothermicexothermic..
Phase ChangesPhase Changes
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Phase ChangesPhase Changes
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Plot of temperature change versus heat added Plot of temperature change versus heat added is a heating curve.is a heating curve.
During a phase change, adding heat During a phase change, adding heat causes no temperature change.causes no temperature change. These points are used to calculate These points are used to calculate HHfusfus and and HHvapvap..
SupercoolingSupercooling: When a liquid is cooled : When a liquid is cooled below its melting point and it still remains below its melting point and it still remains a liquid.a liquid.
Achieved by keeping the temperature low and Achieved by keeping the temperature low and increasing kinetic energy to break increasing kinetic energy to break intermolecular forces.intermolecular forces.
Phase ChangesPhase Changes
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Phase Changes and Heating Phase Changes and Heating CurvesCurves
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Gases liquefied by increasing pressure at Gases liquefied by increasing pressure at some temperature.some temperature.
Critical temperatureCritical temperature: the minimum : the minimum temperature for liquefaction of a gas using temperature for liquefaction of a gas using pressure.pressure.
Critical pressureCritical pressure: pressure required for : pressure required for liquefaction.liquefaction.
Critical Temperature and Critical Temperature and PressurePressure
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Phase Diagrams (P vs T)Phase Diagrams (P vs T)
convenient way to display all of the different phases of a substance convenient way to display all of the different phases of a substance phase phase
diagram for diagram for waterwater
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Phase Diagrams (P vs T)Phase Diagrams (P vs T)
phase phase diagram diagram for for carbon carbon dioxidedioxide
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Synthesis QuestionSynthesis Question
Maxwell House Coffee Company Maxwell House Coffee Company decaffeinates its coffee beans using an decaffeinates its coffee beans using an extractor that is 7.0 feet in diameter and extractor that is 7.0 feet in diameter and 70.0 feet long. Supercritical carbon 70.0 feet long. Supercritical carbon dioxide at a pressure of 300.0 atm and dioxide at a pressure of 300.0 atm and temperature of 100.0temperature of 100.000C is passed through C is passed through the stainless steel extractor. The the stainless steel extractor. The extraction vessel contains 100,000 extraction vessel contains 100,000 pounds of coffee beans soaked in water pounds of coffee beans soaked in water until they have a water content of 50%. until they have a water content of 50%.
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Synthesis QuestionSynthesis Question
This process removes 90% of the caffeine This process removes 90% of the caffeine in a single pass of the beans through the in a single pass of the beans through the extractor. Carbon dioxide that has passed extractor. Carbon dioxide that has passed over the coffee is then directed into a over the coffee is then directed into a waterwater column that washes the caffeine column that washes the caffeine from the supercritical COfrom the supercritical CO22. How many . How many
moles of carbon dioxide are present in the moles of carbon dioxide are present in the extractor?extractor?
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Synthesis QuestionSynthesis Question
L 107.633
mL) L/1000 )(1mL/cm )(1cm10(7.633
(2134cm)06.7cm)(3.1416)(1hr vesselof Volume
cm 2134 cm/ft) ft)(30.48 (70.0 vesselofLength
cm 106.7 cm/2 213.4 vesselof Radius
cm 213.4cm/ft) ft)(30.48 (7.0 vesselofDiameter
4
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22
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Synthesis QuestionSynthesis Question
2
K molatm L
4
CO of mol 748,000n
K 3730.08206
L 107.633atm 300RT
PVn
nRTPV
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Group QuestionGroup Question
How many COHow many CO22 molecules are there in 1.0 molecules are there in 1.0
cmcm3 3 of the Maxwell House Coffee of the Maxwell House Coffee Company extractor? How many more COCompany extractor? How many more CO22
molecules are there in a cmmolecules are there in a cm33 of the of the supercritical fluid in the Maxwell House supercritical fluid in the Maxwell House extractor than in a mole of COextractor than in a mole of CO22 at STP? at STP?