Download - 1 CHAPTER 9 Liquids and Solids Liquids and Solids

11

CHAPTER 9CHAPTER 9

Liquids and SolidsLiquids and Solids

22

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

33

Description of Liquids & Solids

44

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

55

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

66

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..

77


88

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.

221

d

QQkF

99


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.

1010

Intermolecular AttractionsIntermolecular Attractions

Dipole-dipole interactionsDipole-dipole interactions consider NHconsider NH33 a very polar molecule a very polar molecule

1111


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).

1212

Intermolecular AttractionsDispersion Forces

1313

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.


1414


1515

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.

1616


Hydrogen bondingHydrogen bonding consider Hconsider H22OO

1717

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.


1818

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.


1919

Hydrogen BondingHydrogen BondingIntermolecular Attractions

2020

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.


2121

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


2222

Comparing Intermolecular Attractions

2323


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

2424

Intermolecular Attractions and Intermolecular Attractions and Phase ChangesPhase Changes

Na F Ca F Ca O+ - 2+2

2+ 2-

2525

Intermolecular Attractions and Intermolecular Attractions and Phase ChangesPhase Changes

2626

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

2727

EvaporationEvaporation

2828

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

2929


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.

3030

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.


3131

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.


3232

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.


3333

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

3434

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.

3535

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

3636

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

3737

The Liquid StateThe Liquid State

3838

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

3939

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.


4040

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..


4141


4242

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.


4343

Phase Changes and Heating Phase Changes and Heating CurvesCurves

4444

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

4545

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

4646

Phase Diagrams (P vs T)Phase Diagrams (P vs T)

phase phase diagram diagram for for carbon carbon dioxidedioxide

4747

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%.

4848


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?

4949


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

337

22

5050


2

K molatm L

4

CO of mol 748,000n

K 3730.08206

L 107.633atm 300RT

PVn

nRTPV

5151

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?

Download - 1 CHAPTER 9 Liquids and Solids Liquids and Solids

Top Related