Introductory Chemistry , 2 nd Edition Nivaldo Tro

Roy KennedyMassachusetts Bay Community College

Wellesley Hills, MA

Introductory Chemistry, 2nd EditionNivaldo Tro

Chapter 12Liquids and Solids

2006, Prentice Hall

Tro's Introductory Chemistry, Chapter 12

2

Interactions Between Molecules

• many of the phenomena we observe are related to interactions between molecules that do not involve a chemical reactionyour taste and smell organs work because

molecules in the thing you are sensing interact with the receptor molecule sites in your tongue and nose

• in this chapter we will examine the physical interactions between molecules and the factors that effect and influence them


3

The Physical States of Matter

• matter can be classified as solid, liquid or gas based on what properties it exhibits

State Shape Volume Compress Flow

Solid Fixed Fixed No No

Liquid Indef. Fixed No Yes

Gas Indef. Indef. Yes Yes

•Fixed = keeps shape when placed in a container, •Indefinite = takes the shape of the container

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4

Structure Determines Properties• the atoms or molecules have different

structures in solids, liquid and gases, leading to different properties


5

Properties of the States of MatterGases

• low densities compared to solids and liquids

• fluidthe material exhibits a smooth, continuous flow

as it moves

• take the shape of their container

• expand to fill their container

• can be compressed into a smaller volume


6

Properties of the States of MatterLiquids

• high densities compared to gases• fluid

the material exhibits a smooth, continuous flow as it moves

• take the shape of their container• keep their volume, do not expand to fill their

container• can not be compressed into a smaller volume


7

Properties of the States of MatterSolids

• high densities compared to gases• nonfluid

they move as entire “block” rather than a smooth, continuous flow

• keep their own shape, do not take the shape of their container

• keep their own volume, do not expand to fill their container

• can not be compressed into a smaller volume


8

The Structure of Solids, Liquid and Gases


9

Gases

• in the gas state, the particles have complete freedom from each other

• the particles are constantly flying around, bumping into each other and the container

• in the gas state, there is a lot of empty space between the particleson average


10

Gases• because there is a lot of empty space, the

particles can be squeezed closer together – therefore gases are compressible

• because the particles are not held in close contact and are moving freely, gases expand to fill and take the shape of their container, and will flow


11

Liquids• the particles in a liquid are closely

packed, but they have some ability to move around

• the close packing results in liquids being incompressible

• but the ability of the particles to move allows liquids to take the shape of their container and to flow – however they don’t have enough freedom to escape and expand to fill the container


12

Solids• the particles in a solid are packed close

together and are fixed in positionthough they are vibrating

• the close packing of the particles results in solids being incompressible

• the inability of the particles to move around results in solids retaining their shape and volume when placed in a new container; and prevents the particles from flowing


13

Solids• some solids have their particles

arranged in an orderly geometric pattern – we call these crystalline solidssalt and diamonds

• other solids have particles that do not show a regular geometric pattern over a long range – we call these amorphous solidsplastic and glass


14

Why is Sugar a Solid ButWater is a Liquid?

• the state a material exists in depends on the attraction between molecules and their ability to overcome the attraction

• the attractive forces between ions or molecules depends on their structure the attractions are electrostaticdepend on shape, polarity, etc.

• the ability of the molecules to overcome the attraction depends on the amount of kinetic energy they possess


15

Properties of LiquidsViscosity

• some liquids flow more easily than others

• the resistance of a liquid to flow we call viscosity

• larger the attractive forces between the molecules = larger the viscosity

• also, molecules whose shape is not round will have a larger viscosity


16

Properties of LiquidsSurface Tension

• liquids tend to minimize their surface – a phenomenon we call surface tension

• this tendency causes liquids to have a surface that resists penetration


17

Surface Tension• molecules in the interior of a liquid

experience attractions to surrounding molecules in all directions

• but molecules on the surface experience an imbalance in attractions, effectively pulling them in

• to minimize this imbalance and maximize attraction, liquids try to minimize the number of molecules on the exposed surface by minimizing their surface area

• stronger attractive forces between the molecules = larger surface tension


18

Forces of Attraction within a Liquid

• Cohesive Forces = forces that try to hold the liquid molecules to each othersurface tension

• Adhesive Forces = forces that bind a substance to a surfacecapillary actionmeniscus


19

Escaping from the Surface• the process of molecules of a

liquid breaking free from the surface is called evaporationalso known as vaporization

• evaporation is a physical change in which a substance is converted from its liquid form to its gaseous formthe gaseous form is called a vapor


20

Evaporation• over time, liquids evaporate – the molecules of

the liquid mix with and dissolve in the air

• the evaporation happens at the surface

• molecules on the surface experience a smaller net attractive force than molecules in the interior

• but all the surface molecules do not escape at once, only the ones with sufficient kinetic energy to overcome the attractions will escape


21

Factors Effecting the Rate of Evaporation

• increasing the surface area increases the rate of evaporation

• increasing the temperature increases the rate of evaporation

• weaker attractive forces between the molecules = faster rate of evaporation

• liquids that evaporate quickly are called volatile liquids, while those that do not are called nonvolatile

22

Escaping the Surface• the average kinetic energy is directly proportional to

the kelvin temperature• but not all molecules in the sample have the same

kinetic energy• those molecules on the surface that have enough kinetic

energy will escape raising the temperature increases the number of molecules

with sufficient energy to escape


23

Escaping the Surface

• since the higher energy molecules from the liquid are leaving, the total kinetic energy of the liquid decreases, and the liquid cools

• the remaining molecules redistribute their energies, generating more high energy molecules

• the result is the liquid continues to evaporate


24

Reconnecting with the Surface

• when a liquid evaporates in a closed container, the vapor molecules are trapped

• the vapor molecules may eventually bump into and stick to the surface of the container or get recaptured by the liquid – this process is called condensationa physical change in which a gaseous form is

converted to a liquid form


25

Dynamic Equilibrium

• evaporation and condensation are opposite processes

• eventually, the rate of evaporation and condensation in the container will be the same

• opposite processes that occur at the same rate in the same system are said to be in dynamic equilibrium


26

Evaporation and Condensation

When water is justadded to the flask andit is capped, all thewater molecules arein the liquid.

Shortly, the waterstarts to evaporate.Initially the speedof evaporation ismuch faster than speed of condensation

Eventually the condensation andevaporation reachthe same speed.The air in the flaskis now saturatedwith water vapor.

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27

Vapor Pressure• once equilibrium is reached, from that time

forward, the amount of vapor in the container will remain the sameas long as you don’t change the conditions

• the partial pressure exerted by the vapor is called the vapor pressure

• the vapor pressure of a liquid depends on the temperature and strength of intermolecular attractions

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28

Boiling• in an open container, as you heat a

liquid the average kinetic energy of the molecules increases, giving more molecules enough energy to escape the surfaceso the rate of evaporation increases

• eventually the temperature is high enough for molecules in the interior of the liquid to escape – a phenomenon we call boiling


29

Boiling Point• the temperature at which the vapor pressure

of the liquid is the same as the atmospheric pressure is called the boiling pointthe normal boiling point is the temperature

required for the vapor pressure of the liquid to be equal to 1 atm

• the boiling point depends on what the atmospheric pressure isthe temperature of boiling water on the top of a

mountain will be cooler than boiling water at sea level


30

Temperature and Boiling• as you heat a liquid, its

temperature increases until it reaches the boiling point

• once the liquid starts to boil, the temperature remains the same until it all turns to a gas

• all the energy from the heat source is being used to overcome the attractive forces in the liquid


31

Energetics of Evaporation• as it loses the high energy molecules through

evaporation, the liquid cools• then the liquid absorbs heat from its surroundings to

raise its temperature back to the same as the surroundings

• processes in which heat flows into a system from the surroundings are said to be endothermic

• as heat flows out of the surroundings, it causes the surroundings to coolas alcohol evaporates off your skin, it causes your skin to

cool


32

Energetics of Condensation• as it gains the high energy molecules through

condensation, the liquid warms• then the liquid releases heat to its surroundings

to reduce its temperature back to the same as the surroundings

• processes in which heat flows out of a system into the surroundings are said to be exothermic

• as heat flows into the surroundings, it causes the surroundings to warm


33

Heat of Vaporization• the amount of heat needed to vaporize one mole of a

liquid is called the heat of vaporizationHvap

it requires 40.7 kJ of heat to vaporize one mole of water at 100°C

endothermic

Hvap depends on the initial temperature

• since condensation is the opposite process to evaporation, the same amount of energy is transferred but in the opposite directionHcond = -Hvap


34

Heats of Vaporization of Liquidsat their Boiling Points and at 25°C

LiquidChemicalFormula

Normal Boiling

Point, °C

Hvap at Boiling Point,

(kJ/mol)

Hvap at 25°C,

(kJ/mol)

water H2O 100 40.7 44.0

isopropyl alcohol

C3H7OH 82.3 39.9 45.4

acetone C3H6O 56.1 29.1 31.0

diethyl ether

C4H10O 34.5 26.5 27.1

Example 12.1:Using Heat of Vaporization

in Calculations


36

Example:• Calculate the amount of water in grams that can be

vaporized at its boiling point with 155 kJ of heat.


37

Example:Calculate the amount of water in grams that can be vaporized at its boiling point with 155 kJ of heat.

• Write down the given quantity and its units.

Given: 155 kJ


38

• Write down the quantity to find and/or its units.

Find: ? g H2O

Information

Given: 155 kJ



39

• Collect Needed Conversion Factors:

Hvap = 40.7 kJ/mol 40.7 kJ 1 mol H2O

18.02 g H2O = 1 mol H2O

Information

Given: 155 kJ

Find: g H2O



40

• Write a Solution Map for converting the units :

kJ mol H2O g H2O

kJ 40.7

OH mol 1 2

OH mol 1

OH g 0218

2

2.

Information

Given: 155 kJ

Find: g H2O

CF: 40.7 kJ = 1 mol; 18.02 g = 1 mol



41

OH mol 1

OH g 0218

kJ 40.7

OH mol 1kJ 155

2

22 .

• Apply the Solution Map:

= 68.626 g H2O

= 68.6 g H2O • Sig. Figs. & Round:

InformationGiven: 155 kJ

Find: g H2OCF: 40.7 kJ = 1 mol; 18.02 g = 1 molSM: kJ → mol → g



42

• Check the Solution:

155 kJ of heat can vaporize 68.6 g H2O

The units of the answer, g, are correct.The magnitude of the answer makes sense

since it is more than one mole.

InformationGiven: 155 kJ

Find: g H2OCF: 40.7 kJ = 1 mol; 18.02 g = 1 molSM: kJ → mol → g



43

Temperature and Melting• as you heat a solid, its temperature

increases until it reaches the melting point

• once the solid starts to melt, the temperature remains the same until it all turns to a liquid

• all the energy from the heat source is being used to overcome the attractive forces in the solid that hold them in place


44

Energetics of Melting and Freezing• when a solid melts, it absorbs heat from its

surroundings, it is endothermic• as heat flows out of the surroundings, it causes

the surroundings to coolas ice in your drink melts, it cause the liquid to cool

• when a liquid freezes, it releases heat into its surroundings, it is exothermic

• as heat flows into the surroundings, it causes the surroundings to warm


45

Heat of Fusion• the amount of heat needed to melt one mole of a solid is

called the heat of fusionHfus

fusion is an old term for heating a substance until it melts, it is not the same as nuclear fusion

• since freezing is the opposite process to melting, the same amount of energy transferred is the same, but in the opposite directionHcrystal = -Hfus

• in general, Hvap > Hfus because vaporization requires breaking all attractive forces


46

Heats of Fusion of Several Substances

LiquidChemicalFormula

Melting Point, °C

Hfusion, (kJ/mol)

water H2O 0.00 6.02

isopropyl alcohol C3H7OH -89.5 5.37

acetone C3H6O -94.8 5.69

diethyl ether C4H10O -116.3 7.27


47

Sublimation• sublimation is a physical

change in which the solid form changes directly to the gaseous formwithout going through the

liquid form

• like melting, sublimation is endothermic

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IntermolecularAttractive Forces


49

Why are molecules attracted to each other?

• intermolecular attractions are due to attractive forces between opposite charges

• + ion to - ion• + end of polar molecule to - end of polar molecule

H-bonding especially strong

• larger charge = stronger attraction• even nonpolar molecules will have a temporary

induced dipoles


50

Dispersion Forces

• also known as London Forces or Induced Dipoles

• caused by electrons on one molecule distorting the electron cloud on another

• all molecules have dispersion forces

+

----

- -- --

-

++

++

---

--

------

-

--

-

++

++

---

--

-------

--

-

+

----

- -- --

-


51

Instantaneous Dipoles

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Strength of the Dispersion Force

• depends on how easily the electrons can move, or be polarized

• the more electrons and the farther they are from the nuclei, the larger the dipole that can be induced

• strength of the dispersion force gets larger with larger molecules


53

Attractive Forces and Properties• stronger attractive forces between

molecules = higher boiling pointin pure substance

• stronger attractive forces between molecules = higher melting pointin pure substancethough also depends on crystal packing


54

Noble Gas

Molar Mass, (g/mol)

Boiling Point, (K)

He 4.00 4.2

Ne 20.18 27

Ar 39.95 87

Kr 83.80 120

Xe 131.29 165

Dispersion Force and Molar Mass


55

Relationship between Dispersion Force and Molecular Size

-300

-250

-200

-150

-100

-50

0

50

100

150

200

250

1 2 3 4 5 6

Period

Bo

ilin

g P

oin

t, °C

BP, Noble Gas

BP, Halogens

BP, XH4


56

Permanent Dipoles• because of the kinds of

atoms that are bonded together and their relative positions in the molecule, some molecules have a permanent dipole

• all polar molecules have a permanent dipole


57

Dipole-to-Dipole Attraction

• polar molecules have a permanent dipolea + end and a – end

• the + end of one molecule will be attracted to the – end of another


58

MolarMass (g/mol)

Boiling Point, °C

Dipole Size, D

CH3CH2CH3 44 -42 0

CH3-O-CH3 46 -24 1.3

CH3 - CH=O 44 20.2 2.7

CH3-CN 41 81.6 3.9

Polarity and Dipole-to-Dipole Attraction


59

Attractive Forces

+ - + - + - + -

+++

+

____

Dispersion Forces – all molecules

Dipole-to-Dipole Forces – polar molecules


60

Attractive Forces and Properties• Like dissolves Like

miscible = liquids that do not separate, no matter what the proportions

• polar molecules dissolve in polar solventswater, alcohol, CH2Cl2

molecules with O or N higher solubility in H2O due to H-bonding with H2O

• nonpolar molecules dissolve in nonpolar solvents ligroin (hexane), toluene, CCl4

• if molecule has both polar & nonpolar parts, then hydrophilic - hydrophobic competition


61

Immiscible Liquids

When liquid pentane,a nonpolar substance,is mixed with water, a polar substance, the two liquids separatebecause they are moreattracted to their ownkind of molecule thanto the other.


62

Hydrogen Bonding• Molecules that have HF,

OH or NH groups have particularly strong intermolecular attractionsunusually high melting

and boiling pointsunusually high solubility

in water

• this kind of attraction is called a Hydrogen Bond


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Properties and H-Bonding

NameForm-

ula

Molar Mass

(g/mol)Structure

Boiling Point,

°C

Melting Point,

°C

Solubil-

ity in Water

Ethane C2H6 30.0 -88 -172 immisc

Ethanol CH4O 32.0 64.7 -97.8misc-

ble

H C

H

H

C H

H

H

H C

H

H

O H


64

Intermolecular H-Bonding


65

Hydrogen Bonding• When a very electronegative atom is

bonded to hydrogen, it strongly pulls the bonding electrons toward it.

• Since hydrogen has no other electrons, when it loses the electrons, the nucleus becomes deshieldedexposing the proton

• The exposed proton acts as a very strong center of positive charge, attracting all the electron clouds from neighboring molecules


66

H-Bonds vs. Chemical Bonds

• hydrogen bonds are not chemical bonds

• hydrogen bonds are attractive forces between molecules

• chemical bonds are attractive forces that make molecules


67

Relationship between H-bonding and Intermolecular Attraction

-200

-150

-100

-50

0

50

100

150

1 2 3 4 5

Period

Bo

ilin

Po

int,

°C

BP, HX

BP, H2X

BP, H3X

BP, XH4

CH4

NH3

HF

H2O

SiH4

GeH4

SnH4

H2S H2Se

H2Te


68

Molar Mass,

(g/mol)

Boiling Point,

°C

Solubility in water,

(g/100 g H2O) CH3CH2OCH2CH3 74 34.6 7.5

CH3CH2CH2CH2CH3 72 36 INSOL.

CH3CH2CH2CH2OH 74 117 9

Attractive Forces & Properties

69

Types of Intermolecular ForcesType of Force

Relative Strength

Present in Example

DispersionForce

weak, but increases

with molar mass

all atoms and

moleculesH2

Dipole – Dipole Force

moderateonly polar molecules

HCl

Hydrogen Bond

strong

molecules having H bonded to F, O or N

HF


70

Type of Force Type of Interaction Energy(kJ/mol)

Ionic Bond cation + anion 300 - 600Covalent Bond shared electrons 200-400Hydrogen Bond H (bonded to O, N, or F)

attracted to anelectronegative atom

20-40

Ion to Dipole Ion + polar molec. 10-20Dipole to Dipole polar + polar 1-5Ion to Induced ion + nonpolar 1-3Dipole to Induced polar + nonpolar 0.005-2Induced to Induced nonpolar + nonpolar 0.005-2

Crystalline Solids


72

Types of Crystalline Solids


73

Molecular Crystalline Solids• Molecular solids are solids

whose composite units are molecules

• Solid held together by intermolecular attractive forcesdispersion, dipole-dipole, or

H-bonding

• generally low melting points and Hfusion


74

Ionic Crystalline Solids• Ionic solids are solids whose composite

units are formula units• Solid held together by electrostatic

attractive forces between cations and anionscations and anions arranged in a geometric

pattern called a crystal lattice to maximize attractions

• generally higher melting points and Hfusion than molecular solidsbecause ionic bonds are stronger than

intermolecular forces


75

Atomic Crystalline Solids

• Atomic solids are solids whose composite units are individual atoms

• Solid held together by either covalent bonds, dispersion forces or metallic bonds

• melting points and Hfusion vary depending on the attractive forces between the atoms


76

Types of Atomic Solids


77

Types of Atomic SolidsCovalent

• Covalent Atomic Solids have their atoms attached by covalent bondseffectively, the entire solid is one,

giant molecule

• because covalent bonds are strong, these solids have very high melting points and Hfusion

• because covalent bonds are directional, these substances tend to be very hard


78

Types of Atomic SolidsNonbonding

• Nonbonding Atomic Solids are held together by dispersion forces

• because dispersion forces are relatively weak, these solids have very low melting points and Hfusion


79

Types of Atomic SolidsMetallic

• Metallic solids are held together by metallic bonds

• metal atoms release some of their electrons to be shared by all the other atoms in the crystal

• the metallic bond is the attraction of the metal cations for the mobile electronsoften described as islands of

cations in a sea of electrons


80

Metallic Bonding• the model of metallic bonding can be

used to explain the properties of metals

• the luster, malleability, ductility, electrical and thermal conductivity are all related to the mobility of the electrons in the solid

• the strength of the metallic bond varies, depending on the charge and size of the cations – so the melting points and Hfusion of metals vary as well


81

Water A Unique and Important Substance

• water is found in all 3 states on the earth

• as a liquid, it is the most common solvent found in nature

• without water, life as we know it could not existthe search for extraterrestrial life starts with the

search for water


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Water

• liquid at room temperaturemost molecular substances that have a molar

mass (18.02 g/mol) similar to water’s are gaseous

• relatively high boiling point

• expands as it freezesmost substances contract as they freezecauses ice to be less dense than liquid water

Introductory Chemistry , 2 nd Edition Nivaldo Tro

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