ch10 z5e liq solids

Liquids and solids Liquids and solids pp

1

2

10.1 Intermolecular Forces Liquids & solids are similar to each other

compared to gases They are incompressible. Their density doesn’t change (much) with

temperature. These similarities are due

• to the molecules being close together in solids and liquids

• and far apart in gases What holds them close together?

3

Intermolecular forces Within the molecules (intramolecular)

the atoms are bonded to each other. Intermolecular refers to the forces

between the molecules. The intermolecular forces are what hold

the molecules together in the condensed states.

4

Intermolecular forces Strong (these are “intStrong (these are “intrara”)”)

• covalent bondingcovalent bonding• ionic bondingionic bonding

Weak (“intWeak (“interer”)”)• Dipole dipole (including H-bonding).Dipole dipole (including H-bonding).• London dispersion forces.London dispersion forces.

During During phase changesphase changes the the moleculesmolecules stay stay intact (but separate from each other).intact (but separate from each other).

Energy used to overcome forces.Energy used to overcome forces.

5

Dipole - Dipole Remember where the polar definition Remember where the polar definition

came from?came from? Molecules Molecules line upline up in the presence of a in the presence of a

electric field. The opposite ends of the electric field. The opposite ends of the dipole can attract each other so the dipole can attract each other so the molecules stay close together.molecules stay close together.

1% as strong as covalent bonds1% as strong as covalent bonds Weaker with greater distance.Weaker with greater distance. Small role in gases.Small role in gases.

6

+- +-

+-

+

-+

-

+-

+-+-

+-

+-

7

How to show a bond is polar Not a whole charge, just a partial charge means a partially positive means a partially negative

The Cl pulls harder on the electrons The electrons spend more time near the Cl

H Cl

8

Polar Molecules Molecules with a slightly positive and a

slightly negative end Requires two things to be true The molecule must contain polar bonds (This can be determined from

differences in electronegativity).

Symmetry cannot cancel out the effects of the polar bonds.

(Must determine geometry first.)

9

Polar Molecules 98% of the time, the molecule is polar if:1. The molecule has polar bonds and2. There is at least one lone pair on the

central atom.

• Example of an exception to this rule of thumb: CH2O polar because of C=O bond, but no lone pairs

10

Fig 6-26, p.191 Predicting Polarity Tr 37

11

Is it polar?

HF H2O

NH3

CCl4

CO2

a. Yes

b. Yes

c. Yes

d. No

e. No

12

Hydrogen Bonding An An especially strong dipole-dipoleespecially strong dipole-dipole forces forces

when H is attached to when H is attached to F, O, or NF, O, or N Occurs with these three because:Occurs with these three because:

• They have They have high electronegativityhigh electronegativity..• They are They are smallsmall enough to get enough to get closeclose..

The hydrogen partially shares with the The hydrogen partially shares with the lone pairlone pair in the molecule in the molecule nextnext to it. to it.

Affects boiling point.Affects boiling point. The strongest of the intermolecular The strongest of the intermolecular

forces.forces.

13

Hydrogen Bonding

HH

O+ -

+

H HO+-

+

14

Hydrogen bonding

HH

O H HO

HH

O

H

H

OH

HO

H

HO HH

O

15

CH4

SiH4

GeH4SnH4

PH3

NH3 SbH3

AsH3

H2O

H2SH2Se

H2Te

HF

HI

HBrHCl

Boiling Points

0ºC

100

-100

-200

16

Water

+-

+

17

London Dispersion Forces NonNonpolar molecules and noble gases polar molecules and noble gases

also exert forces on each other.also exert forces on each other. Otherwise, no solids or liquids.Otherwise, no solids or liquids. Electrons are Electrons are notnot evenly distributed evenly distributed at at

every instantevery instant in time. in time. Have an Have an instantaneousinstantaneous dipole. dipole. InducesInduces a dipole in the atom next to it. a dipole in the atom next to it. Induced dipole-induced dipole Induced dipole-induced dipole

interaction. interaction. LD2: 6.69LD2: 6.69 Induced dipole in Induced dipole in an oxygen molecule.an oxygen molecule.

18

Example

H H H HH H H H

+ -

H H H H

+ - +

19

Figure 10.5London Dispersion

Forces

20

London Dispersion Forces Weak, short lived.Weak, short lived. Lasts longer at low temperature.Lasts longer at low temperature. Eventually long enough to make liquids.Eventually long enough to make liquids. More electrons means more polarizable.More electrons means more polarizable. Bigger molecules - higher melting & boiling points.Bigger molecules - higher melting & boiling points. Much, much weaker than other forces.Much, much weaker than other forces. Also called Van der Waal’s forces.Also called Van der Waal’s forces. LD 2: 6.72 London Dispersion ForcesLD 2: 6.72 London Dispersion Forces

21

10.2 Liquids Many of the properties due to internal

attraction of atoms.

• Beading

• Surface tension

• Capillary action Stronger intermolecular forces cause

each of these to increase.

22

Surface tension

Molecules in the Molecules in the middlemiddle are are attracted in attracted in allall directions.directions.

Molecules at Molecules at the the toptop are are onlyonly pulled pulled insideinside..

Minimizes surface area.Minimizes surface area.

23

Capillary Action Liquids Liquids spontaneously risespontaneously rise in a in a narrownarrow

tube.tube. Inter molecular forces are Inter molecular forces are cohesivecohesive, ,

connecting connecting likelike things. things. AdhesiveAdhesive forces connect forces connect to something to something

elseelse. (Cohesive - between same . (Cohesive - between same molecules).molecules).

Glass is polar.Glass is polar. So, glass attracts water molecules So, glass attracts water molecules

(adhesive).(adhesive).

25

Beading If a If a polarpolar substance is substance is

placed on a placed on a non-polarnon-polar surface. surface.

• There are There are cohesivecohesive,,

• ButBut nono adhesiveadhesive forces.forces.

And And visa versavisa versa

26

Viscosity How much a liquid How much a liquid resistsresists flowing. flowing. Large forces means Large forces means moremore viscous. viscous. Large molecules can get Large molecules can get tangled uptangled up.. CycloCyclohexane has a hexane has a lowerlower viscosity than viscosity than

hexane because . . . hexane because . . . It is a circle - more compact.It is a circle - more compact.

27

How much of these? Stronger forces bigger effect.

• Hydrogen bonding

• Polar bonding

• LDF

28

Model for Liquids Can’t see molecules so picture them as:Can’t see molecules so picture them as: In motion In motion butbut attracted to each other attracted to each other With regions arranged With regions arranged likelike solids but solids but

• with with higherhigher disorder. disorder.

• with with fewer holes than a gasfewer holes than a gas..

• Highly dynamicHighly dynamic, regions changing , regions changing between types.between types.

29

Phases

The phase of a substance is determined by three things:

The temperature. The pressure. The strength of intermolecular

forces.

30

10.3 Solids Two major types:Two major types: AmorphousAmorphous - those with much - those with much disorderdisorder

in their structure.in their structure. CrystallineCrystalline - have a - have a regular regular

arrangementarrangement of components in their of components in their structure.structure.

31

Crystals Lattice - a three dimensional grid that

describes the locations of the pieces in a crystalline solid.

Unit Cell -The smallest repeating unit in of the lattice.

Three common types . . .

32

Cubic

33

Body-Centered Cubic

34

Face-Centered Cubic

Figure 10.9Three Cubic Unit Cells & the Corresponding Lattices

35

36

Solids There are many There are many amorphousamorphous solids. solids. Like glass.Like glass. We tend to focus onWe tend to focus on crystallinecrystalline solids.solids. Three types:Three types: IonicIonic solids have ions at the lattice points. solids have ions at the lattice points. MolecularMolecular solids have molecules. solids have molecules.

• Can be covalent or network covalentCan be covalent or network covalent Sugar vs. Salt. Sugar vs. Salt. MetallicMetallic (atomic) (atomic)

Figure 10.12Examples of Three Types of Crystalline Solids

Atomic, Ionic and Molecular Solids

37

38

The book drones on about Using diffraction patterns to identify

crystal structures. Talks about metals and the closest

packing model. It is interesting, but trivial. We need to focus on metallic bonding. Why do metal atoms stay together? How does their bonding affect their

properties?

39

10.4 Metallic Bonding The way metal atoms are held together The way metal atoms are held together

in the solid.in the solid. Metals hold onto their valence electrons Metals hold onto their valence electrons

very very weaklyweakly.. Think of the metals as positive ions Think of the metals as positive ions

floating in a floating in a sea of negative electronssea of negative electrons..

40

10.4 Metallic bonding

1s

2s2p

3s

3p

12+ 12+ 12+ 12+12+ 12+

Filled Molecular OrbitalsEmpty Molecular Orbitals

Magnesium Atoms

41


The 1s, 2s, and 2p electrons are close to nucleus, so they are not able to move around.

1s

2s2p

3s

3p

12+ 12+ 12+ 12+12+ 12+

Magnesium Atoms

42


1s

2s2p

3s

3p

12+ 12+ 12+ 12+12+ 12+

Magnesium Atoms

The 3s and 3p orbitals overlap and form molecular orbitals.

43


1s

2s2p

3s

3p

12+ 12+ 12+ 12+12+ 12+

Magnesium Atoms

Electrons in these energy levels can travel freely throughout the crystal.

44


1s

2s2p

3s

3p

12+ 12+ 12+ 12+12+ 12+

Magnesium Atoms

This makes metals conductors

Malleable because the bonds are flexible.

45

Sea of Electrons

+ + + ++ + + +

+ + + +

Electrons are free to move through the solid.

So, metals conduct electricity.

46

Metals are malleable & ductile Malleable - can be hammered into

shape (they bend). Ductile - can be drawn into wires.

47

Malleable

+ + + ++ + + +

+ + + +

48

Malleable

+ + + +

+ + + ++ + + +

Electrons allow atoms to slide by (like ball bearings).

49

Shiny Metals contain many orbitals (d-orbitals)

separated by small energy differences. So, can absorb a wide range of light

frequencies. Electrons then get excited to different

levels because of the wide range of light frequencies.

When de-excited they give off light in that wide range - shiny.

50

Metal Alloys Alloy: contains mixture of elements and

has metallic properties. Substitutional: some host metal atoms

replaced by similar size metal atoms (e.g., Cu/Zn in brass).

Interstitial: Interstices (holes) in closest packed metal structure occupied by small atoms (e.g., C in Fe).

Fig. 10.21p. 468 Two Types of Alloys

51

a. Substitutional

b. Interstitial

52

Metal Alloys

1. Substitutional Alloy: some metal atoms replaced by others of similar size.

brass = Cu/Zn

Substances that have a mixture of elements and Substances that have a mixture of elements and metallic properties.metallic properties.

53

Metal Alloys(continued)

2. Interstitial Alloy: Interstices (holes) in closest packed metal structure are

occupied by small atoms.

steel = iron + carbon

3. Both types: Alloy steels contain a mix of interstitial (carbon) and

substitutional (Cr, Mo) alloys.

54

10.5 Carbon & Silicon: Network Atomic Solids

There are three types of solid carbon. Amorphous - coal uninteresting. Diamond - hardest natural substance on

earth, insulates both heat and electricity.

Graphite - slippery, conducts electricity. How the atoms in these network solids

are connected explains why they have different properties.

55

Diamond- each Carbon is sp3hybridized, connected to four other

carbons. Carbon (diamond)

atoms are locked into tetrahedral shape.

Strong bonds give the huge molecule its hardness.

56

Why is diamond an insulator?

Empty MOs

Filled MOs

EThe space between orbitals make it impossible for electrons to move around.

57

Each carbon is connected to three other

carbons and sp2 hybridized.

So, the molecule is flat with 120º angles in fused 6-member rings.

The bonds extend above and below the plane.

Graphite is different.

58

This bond overlap forms a huge bonding network.

Electrons are free to move through out these delocalized orbitals.

So, the layers slide by each other.

Figure 10.24The p Orbitals

59

Figure 10.22 p. 470The Structures of Diamond and Graphite

60

61

Semiconductors. Like diamond, silicon has an energy gap Like diamond, silicon has an energy gap

between its filled & empty between its filled & empty molecularmolecular orbitals.orbitals.

But, it’s gap is smaller so eBut, it’s gap is smaller so e--s can cross s can cross it at it at room temperatureroom temperature (25 degrees C). (25 degrees C).

Still not great, so it is a Still not great, so it is a semisemiconductorconductor..

62

Semiconductors

Empty MOs

Filled MOs

E

The space between orbitals is closer than with carbon so slightly easier for electrons to move around.

63

Semiconductors

Conductivity is enhanced by doping with group 13 or group 15 elements.

A substance in which some electrons can A substance in which some electrons can cross the band gap.cross the band gap.

64

Semiconductors n-type - doping with atoms with one

more electron (e.g., As) The extra e-s lie close in energy to the

conduction bands and can be easily excited into those levels where they conduct electricity.

Hint: “n-type” as in “negative” because have one more e- .

65

Semiconductors p-typep-type - doping with atoms with - doping with atoms with one lessone less

electron (electron (e.g.,e.g., B) B) An eAn e-- vacancy (hole) is created so as vacancy (hole) is created so as

another eanother e-- enters this hole, it leaves a enters this hole, it leaves a new hole, etc.new hole, etc.

The “hole” advances the opposite The “hole” advances the opposite direction to the movement of edirection to the movement of e-- s. s.

The movement of eThe movement of e-- s causes s causes conduction.conduction.

““pp” as in “” as in “positivepositive” because one ” because one lessless e e-- . .

66

Fig 10.29 p. 476 Silicon Crystal Doped with (a) Arsenic and (b) Boron

(a)(a) Arsenic has one Arsenic has one moremore valence electron than Sivalence electron than Si

(b)(b) Boron has one Boron has one lessless valence valence electron than Sielectron than Si

Electrons must be in Electrons must be in singlysingly occupied molecular orbitals occupied molecular orbitals to conduct a current.to conduct a current.

As an electron fills a hole it As an electron fills a hole it leaves a new hole.leaves a new hole.

67

Figure 10.30 Energy Level Diagrams for (a) an n-Type Figure 10.30 Energy Level Diagrams for (a) an n-Type

Semiconductor and (b) a p-Type SemiconductorSemiconductor and (b) a p-Type Semiconductor

68

Figure 10.31 p. 477The p-n Junction

p-n junction involves contact p-n junction involves contact of p-type & n-type of p-type & n-type semiconductor.semiconductor.

(a)(a) Charge carriers of p-type Charge carriers of p-type region are holes.region are holes.

(b)(b) No current flows (reverse No current flows (reverse bias) - note the terminals bias) - note the terminals have been switched.have been switched.

(c)(c) Current readily flows Current readily flows (forward bias).(forward bias).

Note: each electron that Note: each electron that crosses the boundary crosses the boundary leaves a hole behind. leaves a hole behind. Thus, the electrons and Thus, the electrons and the holes move in the holes move in opposite directions.opposite directions.

69

10.6 Molecular solids. MoleculesMolecules occupy the occupy the cornerscorners of the of the

latticeslattices.. Different molecules have different Different molecules have different

forces between them.forces between them. These forces depend on the These forces depend on the sizesize of the of the

molecule.molecule. They They alsoalso depend on the strength and depend on the strength and

nature of nature of dipole momentsdipole moments..

70

Those without dipoles. Most are Most are gasesgases at 25ºC. at 25ºC. The The only forcesonly forces are are London DispersionLondon Dispersion

Forces (extremely weak).Forces (extremely weak). These depend on These depend on sizesize of atom. of atom. So, large molecules (such as ISo, large molecules (such as I22 ) can be ) can be

solids even without dipoles (lots of esolids even without dipoles (lots of e-- s to s to generate LDFs).generate LDFs).

II2 2 (solid)(solid) Br Br22 (liquid) Cl (liquid) Cl22 (gas) (gas)

large medium smalllarge medium small

71

Those with dipoles. Dipole-dipoleDipole-dipole forces are generally forces are generally

stronger than L.D.F.stronger than L.D.F. Hydrogen-bondingHydrogen-bonding is stronger than is stronger than

Dipole-dipole forces.Dipole-dipole forces. No matter how strong the intermolecular No matter how strong the intermolecular

force, it is always much, much force, it is always much, much weakerweaker than the than the forces in bondsforces in bonds (1%). (1%).

Stronger forces lead to Stronger forces lead to higherhigher melting melting and freezing points. and freezing points.

72

Water is special

HO

H

-

Each molecule has two polar O-H bonds.

73

Water is special

HO

H

Each molecule has two polar O-H bonds.

Each molecule has two lone pair on its oxygen.

74

Water is special Each molecule has two polar O-H

bonds. Each molecule has two lone pair

on its oxygen. Each oxygen can interact with 4

hydrogen atoms.

HO

H

75

Water is special

HO

H

HO

H

HO

H

This gives water an especially high melting and boiling point.

76

10.7 IonicIonic Solids The extremes in dipole-dipole forces-The extremes in dipole-dipole forces-

atoms are actually held together by atoms are actually held together by opposite chargesopposite charges..

So, So, hugehuge melting and boiling points. melting and boiling points. Atoms are Atoms are lockedlocked in lattice, so the solid is in lattice, so the solid is

hard and brittle.hard and brittle. Every eEvery e1-1- is accounted for, so ionic is accounted for, so ionic solidssolids

are are poor conductors poor conductors - good insulators.- good insulators.

77

Using Table 10.7 p. 458, what type of solids do the following form?

DiamondDiamond PHPH33

MgMg NHNH44NONO33

ArAr

a.a. atomic, covalent networkatomic, covalent network

b.b. MolecularMolecular

c.c. Atomic, metallicAtomic, metallic

d.d. IonicIonic

e.e. Atomic, group 8A or 18Atomic, group 8A or 18

78

10.8 Vapor Pressure & Changes of State10.8 Vapor Pressure & Changes of State VaporizationVaporization - change from liquid - change from liquid

to gas to gas atat boiling point. boiling point. EvaporationEvaporation - change from liquid - change from liquid

to gas to gas belowbelow boiling point boiling point Heat (or Enthalpy) of VaporizationHeat (or Enthalpy) of Vaporization

((HHvapvap ) - the energy required to ) - the energy required to

vaporize 1 mol at 1 atm. vaporize 1 mol at 1 atm.

79

VaporizationVaporization Vaporization is an Vaporization is an endothermicendothermic process process

- it requires heat.- it requires heat. Energy is required to overcome Energy is required to overcome

intermolecular forces.intermolecular forces. Responsible for cool earth.Responsible for cool earth. Why we sweat. (Never let them see Why we sweat. (Never let them see

you.)you.)

80

Condensation Change from Change from gas to liquidgas to liquid.. Achieves a dynamic equilibrium with Achieves a dynamic equilibrium with

vaporization in a closed system.vaporization in a closed system. What is a closed system?What is a closed system? A closed system means matterA closed system means matter

can’t go in or out. can’t go in or out. Put a cork in it.Put a cork in it. What the heck is a “What the heck is a “dynamic dynamic

equilibriumequilibrium?”?”

81

Dynamic equilibrium When first sealed the molecules gradually When first sealed the molecules gradually

escape the surface of the liquid.escape the surface of the liquid.

82

Dynamic equilibrium When first sealed the molecules gradually

escape the surface of the liquid. As the molecules build up above the liquid As the molecules build up above the liquid

some condense back to a liquid.some condense back to a liquid.

83


escape the surface of the liquid. As the molecules build up above the liquid

some condense back to a liquid. As time goes by the rate of As time goes by the rate of

vaporization remains constantvaporization remains constant but the rate of condensation but the rate of condensation increases because there are increases because there are more more molecules to condense.molecules to condense.

84


escape the surface of the liquid As the molecules build up above the liquid

some condense back to a liquid. As time goes by the rate of

vaporization remains constant but the rate of condensation increases because there are more molecules to condense.

Equilibrium is reached when:Equilibrium is reached when:

85

Rate of Vaporization = Rate of Condensation

Molecules are constantly changing phase “Dynamic”

The total amount of liquid and vapor remains constant “Equilibrium”

Dynamic equilibrium

86

Figure 10.37The Rates of Condensation and Evaporation

Rate of Rate of evaporation evaporation stays constantstays constant

Rate of Rate of condensation condensation increases as increases as as # vapor as # vapor molecules molecules increase, until increase, until the two rates the two rates are equal.are equal.

87

Vapor pressure The pressure above the liquid at

equilibrium. Liquids with high vapor pressures

evaporate easily. They are called volatile.

Decreases with increasing intermolecular forces because . . . • Bigger molecules (bigger LDF)• More polar molecules (dipole-dipole)

88

Vapor pressure Increases with increasing temperature. Easily measured in a barometer.

89

Dish of Hg

Vacuum

Patm=

760 torr

A barometer will hold a A barometer will hold a column of mercury 760 column of mercury 760 mm high at one atmmm high at one atm

90

Dish of Hg

Vacuum

Patm=

760 torr

A barometer will hold a A barometer will hold a column of mercury 760 column of mercury 760 mm high at one atm.mm high at one atm.

If we inject a volatile If we inject a volatile liquidliquid in the barometer it will in the barometer it will rise to the rise to the toptop of the of the mercury.mercury.

91

Dish of Hg

Patm=

760 torr

A barometer will hold a A barometer will hold a column of mercury 760 column of mercury 760 mm high at one atm.mm high at one atm.

If we inject a volatile liquid If we inject a volatile liquid in the barometer it will in the barometer it will rise to the top of the rise to the top of the mercury.mercury.

There it will vaporize and There it will vaporize and push the column of push the column of mercury down.mercury down.

Water

92

Dish of Hg

736 mm Hg

Water Vapor

The mercury is pushed down by the vapor pressure.

Patm = PHg + Pvap

Patm - PHg = Pvap

760 - 736 = 24 torr

93

Figure 10.38 Vapor Pressure:Which is most volatile?

94

Temperature Effect

Kinetic energy

# of

mol

ecu

les

T1

Energy needed to overcome intermolecular forces

95

Kinetic energy

# of

mol

ecu

les

T1


T1

T2

At higher temperature more molecules have enough energy - higher vapor pressure.


96

Mathematical relationship

ln is the natural logarithm

• ln = Log base e

• e = Euler’s number an irrational number like

Hvap is the heat of vaporization in J/mol

PvapT1 Hvap 1 1ln (-----) = ---- (--- - ---) PvapT2 R T2 T1

97

Mathematical relationship

R = 8.3145 J/K mol (use correct units). Graph = straight line (y = mx + b) Called Clausius-Clapeyron equation. Be able to plot this in a free response

question.

PvapT1 Hvap 1 1ln (-----) = ---- (--- - ---) PvapT2 R T2 T1

98

Figure 10.40

The Vapor Pressure of Water

99

Changes of stateChanges of state The graph of temperature versus heat The graph of temperature versus heat

applied is called a applied is called a heating curveheating curve.. The temperature a solid turns to a liquid The temperature a solid turns to a liquid

is the is the melting pointmelting point.. The The energyenergy required to change required to change solid to solid to

liquidliquid is called the is called the Heat (or Enthalpy) of Heat (or Enthalpy) of Fusion Fusion HHfusfus

The The energyenergy to change to change liquid to gasliquid to gas is is the the Heat of Vaporization Heat of Vaporization HHvapvap

100

Changes of stateChanges of state The graph of temperature versus heat The graph of temperature versus heat

applied is called a applied is called a heating curveheating curve.. Use Use q = m q = m T CT Cpp when the when the temperature temperature

is changingis changing withinwithin a phase. a phase. Use Use q = m q = m HHfusfus when when meltingmelting (no (no

change in temperature)change in temperature) Use Use q = m q = m HHvapvap when when vaporizingvaporizing.. Add them up to get the Add them up to get the overalloverall Heat of Heat of

Vaporization Vaporization HHvapvap

101

-40

-20

0

20

40

60

80

100

120

140

0 40 120 220 760 800

Heating Curve for Water

IceWater and Ice

Water

Water and Steam

Steam

102

-40

-20

0

20

40

60

80

100

120

140

0 40 120 220 760 800

Heating Curve for Water

Heat of Fusion

Heat ofVaporization

Slope is Heat Capacity

103

Figure 10.42 Heating Curve for Water

Bp plateau longer than Mp because takes almost 7x the energy to vaporize as melt.

Slopes of other lines different because different states of water have different molar heat capacities

104

Example Example pp

How much heat does it take to convert 10.0 How much heat does it take to convert 10.0 g of ice at -10 g of ice at -10 C to steam at 150C to steam at 150C?C?

Raise ice temperatureRaise ice temperature to its melting point. to its melting point. q = heat = m x ∆T x Cq = heat = m x ∆T x Cpp = (10.0g)= (10.0g)

(10ºC)(2.06 J/g (10ºC)(2.06 J/g C) =C) = 206 J.206 J. MeltMelt the ice. the ice. q = m x ∆Hq = m x ∆Hff = (10.0 g)(334 J/g) = (10.0 g)(334 J/g) = = 3340 J.3340 J. Raise HRaise H22O temperatureO temperature to its boiling point. to its boiling point. q = heat = m x ∆T x Cq = heat = m x ∆T x Cpp = (10.0g)= (10.0g)

(100ºC)(4.18 J/g (100ºC)(4.18 J/g C) =C) = 4180 J.4180 J.

105

Example Continued Example Continued pp

How much heat does it take to convert 10.0 How much heat does it take to convert 10.0 g of ice at -10 g of ice at -10 C to steam at 150C to steam at 150C?C?

VaporizeVaporize the water. the water. q = m x ∆Hq = m x ∆Hvv = (10.0 g)(2260 J/g) = (10.0 g)(2260 J/g) = = 22 600 J.22 600 J. Raise steam temperatureRaise steam temperature to 150 to 150C.C. q = heat = m x ∆T x Cq = heat = m x ∆T x Cpp

= (10.0g)(50ºC)(2.02 J/g = (10.0g)(50ºC)(2.02 J/g C)C) = = 1010 J.1010 J. Total heat to convert 10.0 g of ice at -10 Total heat to convert 10.0 g of ice at -10 C C

to steam at 150to steam at 150C is the sum of all.C is the sum of all. 206 + 3340 + 4180 + 22 600 + 1010 = 206 + 3340 + 4180 + 22 600 + 1010 = 31 300 J31 300 J

= = 31.3 kJ31.3 kJ

106

Another Phase Change ProblemAnother Phase Change Problem How much energy does it take to How much energy does it take to

convert 0.500 kg ice at -20.0°C to steam convert 0.500 kg ice at -20.0°C to steam at 250.°C?at 250.°C?

CCpp ice = 2.10 J/g°C; steam 2.00 ice = 2.10 J/g°C; steam 2.00

J/g°C; liquid = 4.20 J/g°CJ/g°C; liquid = 4.20 J/g°CHHfusfus = 6.02 kJ/mol = 6.02 kJ/mol

HHvapvap = 40.7 kJ/mol = 40.7 kJ/mol

The answer is . . .The answer is . . . 1680 kJ1680 kJ (z5e508 #87; Sol 247)(z5e508 #87; Sol 247)

107

Melting PointMelting Point Melting point is determined by the vapor Melting point is determined by the vapor

pressure of the pressure of the solid and the liquidsolid and the liquid.. At the melting point the vapor pressure At the melting point the vapor pressure

of the solid of the solid == vapor pressure of the vapor pressure of the liquidliquid

NormalNormal melting point is when the solid & melting point is when the solid & liquid vapor pressures are the same liquid vapor pressures are the same andand totaltotal pressure = pressure = 1 atmosphere1 atmosphere

108

Solid Water

Liquid Water

Water Vapor Vapor

109

Solid Water

Liquid Water

Water Vapor Vapor

If the vapor pressure of the solid is higher than that of the liquid the solid will release molecules to achieve equilibrium.

110

Solid Water

Liquid Water

Water Vapor Vapor

While the molecules of water vapor condense to a liquid.

111

This can only happen if the temperature is above the freezing point since the solid is turning to liquid.

Solid Water

Liquid Water

Water Vapor Vapor

112

If the vapor pressure of the liquid is higher than that of the solid, the liquid will release molecules to achieve equilibrium.

Solid Water

Liquid Water

Water Vapor Vapor

113

Solid Water

Liquid Water

Water Vapor Vapor

While the molecules condense to a solid.

114

The temperature must be below the freezing point since the liquid is turning to a solid.

Solid Water

Liquid Water

Water Vapor Vapor

115

If the vapor pressure of the solid and liquid are equal, the solid and liquid are vaporizing and condensing at the same rate: The melting point.

Solid Water

Liquid Water

Water Vapor Vapor

116

Boiling PointBoiling Point Reached when the vapor pressure Reached when the vapor pressure

equals the equals the externalexternal pressure. pressure. NormalNormal boiling point is the boiling point boiling point is the boiling point

at at 1 atm1 atm pressure. pressure. SuperheatingSuperheating - Heating - Heating aboveabove the the

boilingboiling point. point. SupercoolingSupercooling - Cooling - Cooling belowbelow the the

freezingfreezing point. point.

117

10.9 Phase Diagrams. A plot of temperature versus pressure

for a closed system, with lines to indicate where there is a phase change.

118

Phase Diagram for Water

What happens to BP of water as pressure increases? To FP?

BP increases, FP decreases

What is the definition of triple point?

The T and P at which all 3 states are in equilibrium

119

Temperature

SolidLiquid

Gas

1 Atm

AA

BB

CC

D

D D

Pre

ssur

e

D

120

SolidLiquid

Gas

Triple Point

Critical Point

Temperature

Pre

ssur

e

121

SolidLiquid

Gas

This is the phase diagram for water. The density of liquid water is higher

than solid water (negative slope). Normal boiling point is the boiling

point at 1 atm pressure.

Temperature

Pre

ssur

e

Solid

122

Phase Diagram for Carbon

Note: There are 4 phases:

Diamond, graphite, liquid, vapor.

There are two “triple points”:

Higher one is between Diamond, graphite & liquid

Lower one is between graphite, liquid & vapor

There can be different phases between solids if they have a different crystalline structure.

123

Solid Liquid

Gas

1 Atm

This is the phase diagram for CO2

The solid is more dense than the liquid (positive slope)

The solid sublimes at 1 atm.

Temperature

Pre

ssur

e

124

Z5e Fig 10.52 Phase Diagram for COZ5e Fig 10.52 Phase Diagram for CO22

Solid/Liquid line has Solid/Liquid line has positive slope - Why?positive slope - Why?

Density of solid carbon Density of solid carbon dioxide is greater than dioxide is greater than that of liquid.that of liquid.

ch10 z5e liq solids

Education