Transcript Chapter Seven - Solano Community College

Chapter 12: Liquids,
Solids and Interparticle
Forces
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What is a liquid? A solid?
Properties of liquids and solids depend on Interparticle
(Intermolecular) forces:
- vaporization/condensation/freezing
- equilibrium vapor pressure/volatility
- surface tension
- boiling point/freezing point
We are going to learn about Interparticle or
Intermolecular forces first! (Different order than in
chapter.)
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TYPES OF INTERPARTICLE
FORCES - SEE HANDOUT
All forces of attraction between atoms, ions, molecules
are “Interparticle” forces
Includes ionic bonding, covalent bonding, metallic
bonding, network covalent bonding, and ion-dipole
attraction
Important Subcategory is Intermolecular Forces
Also called Van Der Waal’s forces
Weak to moderate forces of attraction
Not a type of bonding
Includes three main ones: London Dispersion Forces,
Dipole-dipole Attraction and Hydrogen Bonding Force
of Attraction
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Intermolecular Forces
1. London dispersion forces (LDF)
- Small to moderate strength
- Depend on size of electron cloud (and so also
molar mass) of atom or molecule
- Noble gases, diatomic elements, and many
other nonpolar compounds
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Nonpolar molecules such
as H2 can develop
instantaneous dipoles and
induced dipoles. The
attractions between such
dipoles, even through they
are transitory, create
London dispersion forces.
(See figures 12.17 & 18)
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Table 12.4: Dispersion Force and
Molar Mass
Noble
Gas
He
Molar
Mass, (g/mol)
4.00
Boiling
Point, (K)
4.2
Ne
20.18
27
Ar
39.95
87
Kr
83.80
120
Xe
131.29
165
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Relationship between Dispersion Force and Molecular Size
250
200
BP, Noble Gas
150
BP, Halogens
Boiling Point, °C
100
BP, XH4
50
0
1
2
3
4
5
6
-50
-100
-150
-200
-250
-300
Period
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Intermolecular Forces
2. Dipole-dipole attraction
- Moderate strength
- Molecules that have polar covalent bonds
- Polar molecules d+ and d- attraction
Table of Properties of Hydrohalogens
H-F
H-Cl
H-Br
H-I
DEN 1.4
1.1
0.8
0.4
# e-s 10
18
36
54
BP 291
188
206
238
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There are many dipole-dipole interactions possible between
randomly arranged ClF molecules. In each interaction, the
positive end of one molecule is attracted to the negative end
of a neighboring ClF molecule.
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Polarity and
Dipole-to-Dipole Attraction
CH3CH2CH3
MolarMass Boiling Dipole
(g/mol)
Point, °C Size, D
44
-42
0
CH3-O-CH3
46
-24
1.3
CH3 - CH=O
44
20.2
2.7
CH3-CN
41
81.6
3.9
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Intermolecular Forces
3. Hydrogen-bonding force of attraction
(enhanced dipole-dipole)
- Strong force, but much less than real bonding
- Memory helper:
E.T. FON Home: only F-H, O-H and N-H
have this type of force
- Due to small radius and high EN
- See in boiling point data
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Depiction of hydrogen bonding among water
molecules. The dotted lines are
the hydrogen bonds.
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Figures 12.22 & 24:
Intermolecular H-Bonding
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Hydrogen Bonding and Water:
Water - 80% hydrogen-bonded - very tight
arrangement (also high viscosity high density
and high specific heat)
Ice - crystal is very open, less dense than liquid
(4. Dipole - induced dipole between diff types of
molecules, O2 in H2O)
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Diagrams of hydrogen bonding involving selected simple
molecules. The solid lines represent covalent bonds; the
dotted lines represent hydrogen bonds.
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If there were no hydrogen bonding between water molecules,
the boiling point of water would be approximately - 80C.
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Relationship between H-bonding and
Intermolecular Attraction
150
BP, H2X
BP, H3X
H2O
100
Boilin Point, °C
BP, HX
BP, XH4
50
HF
H2Te
0
1
NH3 2
-50
3
H2S
5
H2Se 4
SnH4
-100
GeH4
SiH4
-150
-200
CH4
Period
Notice that molecules with F-H, O-H and N-H have HIGH BPs because
of Hydrogen-bonding forces of attraction.
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Properties and H-Bonding
Name
Ethane
Formula
C2H6
Molar
Mass
30.0
Structure
H
H
H
C
C
H
H
H
BP,
°C
MP,
°C
Sol’b in
Water
-88
-172
immisc
-97.8
miscble
H
Methanol CH3OH 32.0
H
C
H
O
H
64.7
Table on page 411 in Tro.
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Chemistry at a
Glance:
Intermolecular Forces
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PRACTICE IDENTIFYING THE
TYPE OF IM FORCE:
CH4(g)
C6H6(l)
Br2(l)
HBr(l)
IBr(s)
CH3OH(l)
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The Structure of
Solids, Liquid and Gases
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Distinguishing Properties of
Solids, Liquids, and Gases
Property
Solid
Liquid
Gas
Vol/Shape
Def vol
Def vol; indef shape
& def shape
Shape of container
Shape of container
Density
High
High, usually < Solid
Very low
Compressibility
Small
Small
Large
Thermal ExpansionVery small
Small
Moderate
Strength
Strong
Moderate
Weak
Sucrose
Water
Carbon dioxide
Indef vol/shape
of IM Forces
Example
22
There are six changes of state
possible for substances: learn all 6
Fusion
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BP, FP, Phase Changes, and
DHophase
Phase changes: changes of state
Learn all six
Phase changes are accompanied by heat flow, called
Enthalpy of phase change or DHophase
Heat of vaporization: liquid to vapor; energy (J) to
vaporize 1 mol at constant T & P; DHvap for water is
40.7 kJ/mol; DHcond = -DHvap
Heat of fusion: solid to liquid; energy (J) to melt 1 mol at
constant T & P; DHvap for water is 6.02 kJ/mol; DHfrz
= -DHfus
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BP, FP, Phase Changes, and
DHophase
Sensible heat transfer: temperature is changed but not
phase
q = m * cp * DT
m is mass, cp is specific heat and DT is Tf – Ti
Latent heat transfer using DHophase: phase changes but
not temperature
q = m * DHophase
m is mass or moles depending on units
See examples 12.1 and 12.2. Try skill builders.
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BP, FP, Phase Changes, and
DHophase
Specific heat: energy required to raise temperature
of 1.00 gram of substance by 1.00oC
cp for water is 4.184 J/g.oC
Find heat required to raise the temperature of 20.0
g of water from 25.0oC to 35.0oC.
q = 20.0 g (4.184 J/goC)(35.0-25.0)oC
= 837 J
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Practice Calculations
for Heating Curves
Calculate the total heat absorbed when a 15.5 gram cube
of ice melts, warms to the BP of water and then
vaporizes completely. (DHfus = 6.02 kJ/mol; DHvap =
40.7 kJ/mol) There will be two latent heat transfers
and one sensible heat transfer.
Latent: 15.5 g (1mol/18.015g)(6.02kJ/mol) = 5.18 kJ
Sensible: 15.5 g (4.184J/goC)(100.0oC)(1kJ/103J) = 6.49 kJ
Latent: 15.5 g (1mol/18.015g)(40.7kJ/mol) = 35.0 kJ
Total = 46.7 kJ
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BP, FP, Phase Changes, and
DHophase
Boiling point: temperature at which the vapor
pressure of a liquid is equal to the external
pressure above the liquid, usually atmospheric
pressure of 1 atm (Normal BP is at 1 atm)
Freezing point: temperature at which a liquid
changes into a solid at 1 atm
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Boiling Point of Water at
Various Locations That Differ
in Elevation
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In the evaporation of a liquid in a closed container (a), the
liquid level drops for a time (b) and then becomes constant
(ceases to drop). At that point a state of equilibrium has
been reached in which the rate of evaporation equals the rate
of condensation (c).
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Equilibrium Vapor Pressure
In closed system: at any given temperature,
rate of vaporization = rate of condensation
At dynamic equilibrium: number of molecules in gas
phase and number of molecules in liquid phase stay the
same, but processes still happening
Vapor pressure taken at equilibrium = the partial pressure
Vapor pressure changes with change in temperature
Normal boiling point is when vapor pressure is 1.00 atm
or 760. Torr
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Vapor Pressure of Water at
Various Temperatures
Plot vapor pressure curves (pressure vs. temperature): curved line like Figure 11.26. Normal
boiling point is the temperature at which vapor pressure = atm pressure = 760 torr.
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Properties of Liquids
Just read about surface tension, viscosity and
capillary action
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Types of Crystalline Solids
There are two types of solids: crystalline and amorphous. We are
looking at crystalline.
There are FOUR types of crystalline solids:
Molecular: solids made of molecules with covalent bonds;
molecules held in place by IM forces; low to mod MPs
Ionic: solids made of formulas units of ions; held in place by ionic
bonding; high MPs
Metallic: composite units are atoms; held in place with metallic
bonding; range of MP’s but usually higher than molecular solids
Network covalent: atoms held together in network covalent
bonding; only diamond, SiC, SiO2.
(Atomic solids like noble gases do not occur at normal conditions.)
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