Chem 16 General Chemistry 1

09 Liquids, Solids, and Phase Changes

Dr. Gil C. Claudio

First Semester 2014-2015

Table of Contents

Contents

1 Overview of Physical States and Phase Changes 1

2 Intermolecular Forces 2

3 Some Properties of Liquids 63.1 Surface Tension, Viscosity, Capillary Action . . . . . . . . . . . . 63.2 Vaporization and Boiling . . . . . . . . . . . . . . . . . . . . . . . 10

4 Solids 114.1 Types of Solids . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 114.2 Melting and Sublimation . . . . . . . . . . . . . . . . . . . . . . . 14

5 Phase Changes 15

6 Phase Diagrams 15

ReferencesReferences of these notes

General Chemistry, 10th ed, by Ralph H. Petrucci, F. Geoffrey Herring,Jeffy D. Madura, and Carey Bisonnette.

Chemistry: The Central Science, 13th ed., by Theodore L. Brown, H. EugeneLeMay Jr., Bruce E. Bursten, Catherine J. Murphy, Patrick M. Woodward,and Matthew W. Stoltzfus.

1 Overview of Physical States and Phase Changes

Observations in Solids, Liquids, and Gases

1

GAS LIQUID SOLID

Volume of Assumes Own volume Own volumecontainer volume of

container

Shape of Assumes Assumes Own shapecontainer shape of shape of

container container

Compressibility Compressible Incompressible Incompressible

Diffusion Rapidly Slowly Very slowly

Flow Flows readily Flows readily Does not flow

Molecular Explanation

GAS LIQUID SOLID

Space between Empty space. Closer Close togethermolecules Molecules far together

apart

Order of Total disorder Disorder Orderedmolecules arrangement

Freedom of Complete Free relative to Particlesmotion of freedom each other essentially inparticles fixed position

REASON Very low With IFA Strong IFA(or no) IFA

2 Intermolecular Forces

Relative Strengths of Attractive ForcesMelting and Boiling Points of Representative Substances

Force HoldingParticles Together Substance MP (K) BP (K)Chemical bondsIonic bonds Lithium fluoride (LiF) 1118 1949Metallic bonds Beryllium (Be) 1560 2742Covalent bonds Diamond (C) 3800 4300IntermolecularforcesDispersion Nitrogen (N2) 63 77Dipole-dipole Hydrogen chloride (HCl) 158 188Hydrogen-bonding Hydrogen fluoride (HF) 190 293

van der Waals ForcesThe term van der Waals forces is used to describe, collectively,

intermolecular forces of the London type and interactions between permanentdipoles.

Non-Polar MoleculesNon-polar molecules due to

low EN difference between two bonded atoms. e.g., methane CH4

2

symmetric overall geometry, e.g., boron trifluoride BF3

en.wikipedia.org/wiki/File:Methane-CRC-MW-3D-balls.png

en.wikipedia.org/wiki/ File:Boron-trifluoride-elpot-3D-vdW.png

London Dispersion ForcesLondon Dispersion Forces (or simply dispersion forces) are the

intermolecular forces resulting from attractions between instantaneous andinduced dipoles.

Fritz London (1930)

2+

e-

e-

2+

e-

e-

PolarizabilityPolarizability is the ease with which the electron cloud of an atom or a

molecule is distorted by an outside influence, thereby inducing the dipolemoment.

The greater the polarizability of the molecule, the more easily its electroncloud can be distorted to give a momentary dipole, which leads tostronger LDF.

The bigger the electron cloud, higher polarizability, thus stronger LDF.Bigger molecules have higher IFA.

Electrons in elongatedmolecules are more easily displaced than are thosein small, compact, symmetrical molecules. More polarizable, strongerLDF, higher IFA.

Polarizability in Pentanesn-Pentane C5H12 bp = 36.1

C Neopentane C5H12 bp = 9.5C

3

en.wikipedia.org/wiki/File:Pentane-3D-space-filling.png

commons.wikimedia.org/wiki/File:Neopentane 3D 1.png

Gecko on Glass

commons.wikimedia.org/wiki/File:Gecko Leaftail 1.jpg

Polar MoleculesA dipole is molecule with one end having a slight negative charge and the

other end having a slight positive charge.

1. EN difference between two bonded atoms polarity within the bond

2. overall geometry of the molecule

en.wikipedia.org/wiki/File:Hydrogen-fluoride-elpot-transparent-3D-balls.png

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Water and Ammonia

en.wikipedia.org/wiki/ File:Water-elpot-transparent-3D-balls.png

en.wikipedia.org/wiki/ File:Ammonia-elpot-transparent-3D-balls-A.png

Dipole-Dipole Interactions

+ -

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+

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Ion-Dipole Interactions

+ - +

++

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+

+

+

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Hydrogen BondHydrogen bonding is the bonding that results from the intermolecular

attractions between molecules containing hydrogen bonded to anelectronegative element. The most important examples involve oxygen,nitrogen, and fluorine.

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Hydrogen Bonds in Water

+

+

++

en.wikipedia.org/wiki/File:3D model hydrogen bonds in water.svg

Butane and AcetoneTwo molecules with molar mass of 58 amu

Butane C4H10, bp = 0.5C

Acetone C3H6O,bp = 56.2C

en.wikipedia.org/wiki/File:Butane-3D-balls.png

en.wikipedia.org/wiki/File:Butane-3D-balls.png

Summary of van der Waals Forces

LDF exist between all molecules. Displacements of electrons inmolecules. Increase with increasing molecular mass. Depend onmolecular shapes.

Permanent dipoles. Displacements of electron pairs in bonds rather thanin molecules as a whole, resultant dipole moments.

For substances of comparable molecular masses, dipole forces canproduce significant differences in properties such as melting point,boiling point, and enthalpy of vaporization.

When comparing substances of widely different molecular masses,dispersion forces are usually more significant than dipole forces.

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3 Some Properties of Liquids

3.1 Surface Tension, Viscosity, Capillary Action

Surface TensionSurface Tension is the intermolecular, cohesive attraction that causes a

liquid to minimize the surface area.

en.wikipedia.org/wiki/File:Surface tension March 2009-3.jpg

Surface Tension: Molecular View

en.wikipedia.org/wiki/File:WassermolekuleInTopfchen-2.svg

Water Strider

en.wikipedia.org/wiki/File:WaterstriderEnWiki.jpg

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ViscosityViscosity is a measure of the resistance of fluids to flow.

measured by timing how long it takes a certain amount of liquid to flowthrough a thin tube under gravitational force.

related to the ease with which individual molecules of the liquid canmove with respect to one another

also related to structural features that cause themolecules to be entangledduring flow.

Honey

en.wikipedia.org/wiki/File:Runny hunny.jpg

Viscosities of HydrocarbonsViscosities of a Series of Hydrocarbons at 20C

Substance Formula Viscosity(kg/m-s)

Hexane CH3CH2CH2CH2CH2CH3 3.26 104

Heptane CH3CH2CH2CH2CH2CH2CH3 4.09 104

Octane CH3CH2CH2CH2CH2CH2CH2CH3 5.42 104

Nonane CH3CH2CH2CH2CH2CH2CH2CH2CH3 7.11 104

Decane CH3CH2CH2CH2CH2CH2CH2CH2CH2CH3 1.42 103

Cohesive and Adhesive ForcesCohesive forces are intermolecular forces between like molecules, such as

within a drop of liquid.

Adhesive forces are intermolecular forces between unlike molecules, such asmolecules of a liquid and of a surface with which it is in contact.

If cohesive forces are strong compared with adhesive forces, a drop maintainsits shape. If adhesive forces are strong enough, the energy requirement forspreading the drop into a film is met through the work done by the collapsingdrop.

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Hydrophobic EffectThe hydrophobic effect is the observed tendency of nonpolar substances

to aggregate in aqueous solution and exclude water molecules.

The name, literally meaning water-fearing, describes the segregationand apparent repulsion between water and nonpolar substances.

The hydrophobic effect explains the separation of a mixture of oil andwater into its two components, and the beading of water on nonpolarsurfaces such as waxy leaves.

Hydrophobic Leaf

upload.wikimedia.org/wikipedia/commons/8/8c/Dew 2.jpg

Hydrophobicity of Surfaces

en.wikipedia.org/wiki/File:Surface tension.svg

Capillary ActionCapillary action, or capillarity, is the ability of a liquid to flow against

gravity where liquid spontaneously rise in a narrow space such as between thehairs of a paint-brush, in a thin tube, in porous material such as paper, in somenon-porous materials such as liquefied carbon fiber, or in a cell.

This effect can cause liquids to flow against the force of gravity, sun orthe magnetic field induction.

It occurs because of inter-molecular attractive forces between the liquidand solid surrounding surface;

If the diameter of the tube is sufficiently small, then the combination ofsurface tension (which is caused by cohesion within the liquid) and forceof adhesion between the liquid and container act to lift the liquid.

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Capillarity

en.wikipedia.org/wiki/File:Capillarity.svg

3.2 Vaporization and Boiling

VaporizationVaporization is the passage of molecules from the liquid to the gaseous

state.

Liquid molecules having kinetic energies sufficiently above the averagevalue are able to overcome intermolecular forces of attraction and escapefrom the surface of the liquid into the gaseous state.

Vaporization occurs more readily with

increased temperature

increased surface area of the liquid

decreased IFA

Enthalpy of VaporizationThe enthalpy of vaporization is the quantity of heat that must be absorbed

if a certain quantity of liquid is vaporized at a constant temperature. Alwaysendothermic, > 0.

Hvap = Hvapor Hliquid

The conversion of a gas or vapor to a liquid is called condensation. Alwaysexothermic, < 0.

Hcondensation = Hvap

Vapor PressureVapor pressure is the pressure exerted by a vapor when it is in dynamic

equilibrium with its liquid at a fixed temperature.

Liquids with high vapor pressures at room temperature are said tobe volatile, and those with very low vapor pressures are nonvolatile.Depends on IFA.

As an excellent first approximation, the vapor pressure of a liquiddepends only on the particular liquid and its temperature, and not onthe amount of liquid nor the amount of vapor, as long as some of each ispresent at equilibrium.

Vapor pressure increases with temperature.

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Clausius-Clapeyron EquationThe liquid-vapor curve of P-vs-T is described by the Clausius-Clapeyron

equation

ln

(P2P1

)=

Hvap

R

(1

T2

1

T1

)

The plot is a straight line (y = mx + b), with y ln 1/P and x 1/T.

Applying the Clausius-Clapeyron EquationPHMB 10e, Example 12-5, pp 516-517

Calculate the vapor pressure of water at 35C, given that the vaporpressure of water at 313.2 K is 55.3 mmHg, that Hvap = 44.0 kJ/mol, and thatR = 8.3145 J/mol-K.

ANSWER: 41.9 mmHg

Vapor Pressure of WaterVapor pressure of water at various temperatures

T (C) P (mmHg) T (C) P (mmHg) T (C) P (mmHg)0.0 4.6 29.0 30.0 93.0 588.610.0 9.2 30.0 31.8 94.0 610.920.0 17.5 40.0 55.3 95.0 633.921.0 18.7 50.0 92.5 96.0 657.622.0 19.8 60.0 149.4 97.0 682.123.0 21.1 70.0 233.7 98.0 707.324.0 22.4 80.0 355.1 99.0 733.225.0 23.8 90.0 525.8 100.0 760.026.0 25.2 91.0 546.0 110.0 1074.627.0 26.7 92.0 567.1 120.0 1489.128.0 28.3

BoilingBoiling is a process in which vaporization occurs throughout a liquid. It

occurs when the vapor pressure of a liquid is equal to barometric pressure.

The normal boiling point is the temperature at which the vapor pressure ofa liquid is 1 atm. It is the temperature at which the liquid boils in a containeropen to the atmosphere at a pressure of 1 atm.

4 Solids

4.1 Types of Solids

Network Covalent SolidsA network covalent solid is a substance in which covalent bonds extend

throughout the crystal, making the covalent bond both an intramolecular andan intermolecular force.

e.g., the two allotropes of carbondiamond and graphite

Diamond and Graphite

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en.wikipedia.org/wiki/File:Diamond and graphite2.jpg

Allotropes of Carbon

commons.wikimedia.org/wiki/File:Eight Allotropes of Carbon.png

1. Diamond

2. Graphite

3. Lonsdaleite

4. C60

5. C540

6. C70

7. Amorphous carbon

8. single-walled carbon nanotube

Crystalline SolidA crystalline solid (or simply crystal) is a solidwhose internal arrangement

of atoms, molecules, or ions possesses a regularly repeating pattern in anydirection through the solid.

usually have flat surfaces (or faces) that make definite angles with oneanother, thus they have highly regular shapes. E.g., NaCl, quartz, anddiamond.

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Metallic SolidsMetallic solids (or simplymetals) consist entirely of metal atoms.

Metallic bonding happens because the valence electrons are delocalizedthroughout the entire solid. That is, the valence electrons are notassociated with specific atoms or bonds but are spread throughout thesolid. In fact, we can visualize a metal as an array of positive ionsimmersed in a sea of delocalized valence electrons.

The electrons are confined to the metal by electrostatic attractions to thecations, and they are uniformly distributed throughout the structure.

Metallic bonding is stronger than dispersion forces, but there are noteenough valence electrons to form covalent bonds between atoms.

Electron Sea Model

Electrical conductivity. The electrons are mobile. With an appliedvoltage, the electrons flow through the metal toward the positivelycharged end of the wire.

Thermal conductivity. The movement of electrons permits readytransfer of kinetic energy throughout the solid.

Malleability and ductility. Metal atoms form bonds to many neighbors.Changes in the positions of the atoms due to reshaping the metal arepartly accommodated by a redistribution of electrons.

AlloysAn alloy is a material that contains more than one element and has the

characteristic properties of a metal.

It is one of the primary ways of modifying the properties of pure metallicelements.

Nearly all the common uses of iron involve alloy compositions (e.g.,stainless steel).

Bronze is formed by alloying copper and tin.

Brass is an alloy of copper and zinc.

Ionic SolidsIonic solids are held together by the electrostatic attraction between cations

and anions.

The lattice energy measures the energy to break up an ionic crystal andseparate its ions.

The attractive force between a pair of oppositely charged ions increaseswith increased charge on the ions and with decreased ionic sizes.

Characteristics of Crystalline Solids (1)Metallic

structural particles: Cations and delocalized electrons

contributing force: metallic bonds

typical properties: Hardness varies from soft to very hard; melting pointvaries from low to very high; lustrous; ductile; malleable; very goodconductors of heat and electricity

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examples: Na, Mg, Al, Fe, Sn, Cu, Ag, W

Ionic

structural particles: cations and anions

contributing force: electrostatic attractions

typical properties: Hard; moderate to very high melting points;nonconductors as solids, but good electric conductors as liquids; manyare soluble in polar solvents such as water

examples: NaCl, MgO, NaNO3

Characteristics of Crystalline Solids (2)Network covalent

structural particles: atoms

contributing force: covalent bonds

typical properties: Most are very hard and either sublime or melt at veryhigh temperatures; most are non-conductors of electricity

examples: diamond, graphite, SiC, AlN, SiO2

Molecular: Non-polar

structural particles: atoms or non-polar molecules

contributing force: dispersion forces

typical properties: Soft; extremely low to moderate melting points(depending on molar mass); sublime in some cases; soluble in somenonpolar solvents

examples: He, Ar, H2, CO2, CCl4, CH4, I2

Characteristics of Crystalline Solids (3)Molecular: polar

structural particles: polar molecules

contributing force: dispersion forces and dipole-dipole interactions

typical properties: Low to moderate melting points; soluble in somepolar and some nonpolar solvents

examples: (CH3)2O, CHCl3, HCl

Molecular: Hydrogen bonded

structural particles: molecules with H bonded to N, O, or F

contributing force: hydrogen bonds

typical properties: Low to moderate melting points; soluble in somehydrogen-bonded solvents and some polar solvents

examples: H2O, NH3

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4.2 Melting and Sublimation

Melting PointMelting is the transition of a solid to a liquid and occurs at the melting

point.

The quantity of heat required to melt a solid is the enthalpy of fusionHfus

Freezing is the conversion of a liquid to a solid that occurs at a fixedtemperature known as the freezing point.

The melting point and freezing point of a substance are identical.

The enthalpy of fusion of water is 6.01 kJ/mol

H2O(s) H2O(l) Hfus = 6.01 kJ/mol

Sublimation and DepositionSublimation is the passage of molecules from the solid to the gaseous state.

The enthalpy of sublimation Hsub is the quantity of heat needed toconvert a solid to vapor.

Hsub = Hfus + Hvap

The Clausius-Clapeyron can also be used for sublimation.

Deposition is the passage of molecules from the gaseous to the solid state.

5 Phase Changes

Phase ChangesThe state of matter depends on:

1. IFA. Depends on the nature of the substance.

2. Temperature. Determines the kinetic energy of the molecules.

Phase changes are the change of a substance from one state of matter toanother.

Plasma

Gas

Solid

Liquid

En

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De

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VaporizationCondensation

en.wikipedia.org/wiki/File:Phase change - en.svg

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Calculating H for Temperature and Phase ChangesBLBMWS 13e, Exercise 11.3, p 460

Calculate the enthalpy change upon converting 1.00 mol of ice at 25C tosteam at 125C under a constant pressure of 1 atm. The specific heats of ice,liquid water, and steam are 2.03, 4.18, and 1.84 J/g-K, respectively. For H2O,Hfus = 6.01 kJ/mol and Hvap = 40.67 kJ/mol.

ANSWER: 56.0 kJ

6 Phase Diagrams

Phase DiagramsA phase diagram is a graphical representation of the conditions of

temperature and pressure at which solids, liquids, and gases (vapors) exist,either as single phases or states of matter or as two or more phases inequilibrium.

Features of a Phase DiagramThe lines that separate the three regions indicate pressures and

temperatures at which two phases can coexist at equilibrium.

called the lines of equilibrium or phase boundaries. Phase transitionsoccur along these lines. For example, the solid-gas coexistence curvespecifies the vapor pressure of the solid as a function of pressure.

Themelting point at 1 atm is the normal melting point Themelting pointat 1 bar is the standard melting point.

Same for normal and standard boiling point.

At the triple point, the three lines in the phase diagram intersect at which solid,liquid, and gas coexist in equilibrium.

Triple PointThe triple point of a substance is the temperature and pressure at which the

three phases (gas, liquid, and solid) of that substance coexist in thermodynamicequilibrium.

http://www.fphoto.com/site/asset/slideshow/ Fphoto-43349706J-2RMd.jpg

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Critical PointThe critical point refers to the temperature and pressure at which a liquid

and its vapor become identical. It is the highest temperature point on the vaporpressure curve.

The density of the liquid decreases, that of the vapor increases, andeventually the two densities become equal.

The surface tension of the liquid approaches zero. The interface betweenthe liquid and vapor becomes less distinct and eventually disappears.

A supercritical fluid is any substance at a temperature and pressure above itscritical point, where distinct liquid and gas phases do not exist.

Critical Temperature and PressureThe temperature and pressure at the critical point are the critical

temperature Tc and the critical pressure Pc.

For water, Tc = 647 K (374C) and Pc = 218 atm.

At any temperature above Tc, liquid and vapor phases cannot coexistin equilibrium, and isothermal compression of the vapor will not causecondensation, in contrast to compression below Tc.

Critical CO2

commons.wikimedia.org/wiki/File:Critical carbon dioxide.jpg

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