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Chapter 12 Liquids and Solids. 2006, Prentice Hall. Interactions Between Molecules. many of the phenomena we observe are related to interactions between molecules that do not involve a chemical reaction - PowerPoint PPT Presentation
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2006, Prentice Hall
Chapter 12Liquids
andSolids
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
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• fluid
the 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.
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
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 44.0isopropyl alcohol
C3H7OH 82.3 39.9 45.4
acetone C3H6O 56.1 29.1 31.0diethyl ether
C4H10O 34.5 26.5 27.1
35
OH mol 1OH g 0218
kJ 40.7OH mol 1kJ 155
2
22 .
• Apply the Solution Map:
= 68.626 g H2O
= 68.6 g H2O • Sig. Figs. & Round:
InformationGiven: 155 kJFind: g H2OCF: 40.7 kJ = 1 mol; 18.02 g = 1 molSM: kJ → mol → g
Example:Calculate the amount of water in grams that can be vaporized at its boiling point with 155 kJ of heat.
36
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
37
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
38
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
39
Heats of Fusion of Several Substances
LiquidChemicalFormula
Melting Point, °C
Hfusion, (kJ/mol)
water H2O 0.00 6.02isopropyl alcohol C3H7OH -89.5 5.37acetone C3H6O -94.8 5.69diethyl ether C4H10O -116.3 7.27
40
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
IntermolecularAttractive Forces
42
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
43
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
+----
- -- --
-
++
++
---
--
-------
--
-
++
++
---
--
------
-
--
-
+----
- -- --
-
44
Instantaneous Dipoles
45
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
46
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
47
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
48
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
Boi
ling
Poin
t, °C
BP, Noble Gas
BP, Halogens
BP, XH4
49
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
50
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
51
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
52
Attractive Forces
+ - + - + - + -
+++
+
____
Dispersion Forces – all molecules
Dipole-to-Dipole Forces – polar molecules
53
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
54
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.
55
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
56
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
57
Intermolecular H-Bonding
58
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
59
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
60
Relationship between H-bonding and Intermolecular Attraction
-200
-150
-100
-50
0
50
100
150
1 2 3 4 5
Period
Boi
lin P
oint
, °C
BP, HX
BP, H2X
BP, H3X
BP, XH4
CH4
NH3
HF
H2O
SiH4
GeH4
SnH4
H2S H2Se
H2Te
61
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
62
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
moderate only polar molecules HCl
Hydrogen Bond strong
molecules having H bonded to F, O or N
HF
63
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
65
Types of Crystalline Solids
66
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
67
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
68
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
69
Types of Atomic Solids
70
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
71
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
72
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
73
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
74
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
75
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 freezes
most substances contract as they freezecauses ice to be less dense than liquid water