Chapter 12 Review

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Chapter 12 Review
Examples of Gases O2 N2 CO2 CH4 Cl2 noble gases
He, Ne, Ar etc.
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Properties of Gases
Collections of atoms or molecules in which the
particles are relatively far apart from each other
Relatively little interaction between particles
Gases flow
Gases are compressible (can squeeze on the gas to
cause the volume to decrease and the pressure to
increase)
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Ideal Gas Equation
PV nRT
P pressure (atm, torr, mm Hg, pascal etc.)
V volume (L, mL, cm3)
n moles
R gas constant (0.08206 L-atm/mol-K, 8.314
J/mol-K)
T temperature (K)
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Ideal Gas Equation (2)
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Ideal Gas Equation (2)
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How To Ensure a Straight Line When Plotting
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Kinetic Molecular Theory of Gases
1. Large number of atoms/molecules in random
motion
2. Volume of particles negligible
3. Interaction between particles negligible
4. Average kinetic energy constant
5. Average kinetic energy proportional to
absolute temperature
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Figure 12.13 Distribution of Speeds
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CHAPTER 13 Intermolecular Forces
Chemistry Chemical Reactivity Kotz Treichel
5th edition
Compare the different states of matter (solid,
liquid, gas) Kinetic-molecular theory assumes
gas particles are far apart and behave
independently from one another. Liquids and
Solids are less "ideal". Compare volumes for
different states (Figures 13.1 and 13.2)
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CHAPTER 13.1 States of Matter
Consider the particulate nature of matter and the
forces that hold particles together.
Intramolecular forces versus Intermolecular
forces and ionic bonding.
Intramolecular forces are those that hold the
molecule together (covalent bonds) and ionic
bonds are due to electrostatic forces between
oppositely charged ions. Metallic bonds are the
forces that hold metal atoms together.
Intermolecular forces are forces that exist
between molecules (relatively weak)
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Intermolecular Forces
Comparison of a covalent bond and an
intermolecular attraction HCl covalent bond 431
kJ/mol between HCl molecules 16 kJ/mol
Ionic bonds 700 to 1000 kJ/mol Covalent bonds
100-400 kJ/mol Intermolecular forces 15 or less
Properties such as boiling points, melting
points, solubility etc. are influenced by the
strength of the intermolecular forces
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Dipole-Dipole Attractions
Dipole-dipole forces are experienced when polar
molecules are close together. The molecules have
permanent dipoles (dipole moments gt 0).
Figure 13.3 Electrostatic interaction of polar
molecules
Figure 13.4 Evaporation/Condensation Consider
the enthalpy changes when the substance undergoes
a phase change. What is enthalpy (H)?
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Other Phase Changes
Endothermic Melting solid to liquid Vaporization
liquid to gas Sublimation solid to
gas Exothermic Freezing liquid to
solid Condensation gas to liquid Deposition gas
to solid
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Dipole-Dipole Attractions (3)
Table 13.1 Compare properties of polar and
nonpolar substances.
Solubility "Like Dissolves Like" (Figure
13.5) e.g. Ethanol and Water mix/Oil and Vinegar
do not
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Dipole/Induced Dipole Forces
Polar molecules like water an induce a dipole in
a nonpolar molecule. (See Figure 13.6)
Process of inducing dipole is Polarization and
depends on the Polarizability of the molecule.
Polarizability is related to how easily the
electron cloud on an atom can be distorted when
it comes in contact with an electric field.
Larger atoms and molecules have bigger electron
clouds and are more polarizable than smaller
atoms and molecules.
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Induced Dipole/ Induced Dipole Forces
Table 13.2 Compare the solubilities of nonpolar
gases in water.
Note that nonpolar molecules and atoms can also
be attracted to one another. The table on page
515 shows heats of vaporization/boiling points
for nonpolar molecules.
The explanation for these attractions relates to
the fact that when nonpolar molecules come in
contact with one another, distortions in the
electron clouds lead to momentary dipoles which
can lead to attractive forces between molecules.
(Figure 13.7)
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Induced Dipole/ Induced Dipole Forces
These forces are often referred to as 'London
Dispersion Forces' (after the scientist who
discovered them) or 'Dispersion Forces'.
Dispersion forces are relatively weak but
increase as the polarizability of the substance
increases. Thus the general rule of thumb is
that the larger the atom or molecule, the larger
the dispersion forces and the higher the
boiling/melting point.
Compare the data on page 515 and in the following
table to see the trend.
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Boiling Points of Halogens
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Influence of Shape
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Hydrogen Bonding
Figure 13.8 Boiling Points of hydrogen-containing
compounds as a function of molecular weight
Hydrogen Bonding a special type of
intermolecular attraction between the H atom in a
polar bond and an unshared electron pair on a
nearby ion or atom
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Trends in Hydrogen Bonding
How is the strength of the H bond influenced by
the element bonded to the H, X H (where X is N,
O, or F) ?
How is the strength influenced by the element
that forms the H bond with the polarized H atom,
X H ??? Y (where Y is N, O, or F) ?
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Trends in Hydrogen Bonding (2)
Strength should increase as the X H bond
dipole increases
N H ??? Y lt O H ??? Y lt F H ??? Y
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Trends in Hydrogen Bonding (3)
The atom Y must possess an unshared electron pair
that attracts the positive end of the X H bond
dipole.
The electron pair must not be too diffuse in
space. The Y atom must be a small, highly
electronegative atom (i.e. N, O, or F)
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Trends in Hydrogen Bonding (4)
The strength increases when the electron pair is
not too strongly attracted to its own nucleus.
X H ??? F lt X H ??? O lt X H ??? N
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Trends in Hydrogen Bonding (5)
When X and Y are the same, the energy of hydrogen
bonding increases in the order
N H ??? N lt O H ??? O lt F H ??? F
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Summary of Intermolecular Forces
Table 13.3 Summary of intermolecular forces
Dispersion forces operate between all molecules.
A polar substance will experience both
dipole-dipole interactions and dispersion forces.
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Predict Order of Boiling Points
List the substances BaCl2, H2, CO, HF, and Ne in
order of increasing boiling points
Highest?
Highest, Ne or CO ?
Highest, HF or CO ?
Lowest?
H2 lt
lt BaCl2
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Properties of Liquids
Vaporization and evaporation Figure 13.12
Distribution of energy among molecules as a
function of energy Heat of vaporization
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Example 13.4
You put 1.00 L of water in a pan at 100 ?C and
the water slowly evaporates. How much heat must
be supplied to vaporize the water? Hvap for water
40.7 kJ/mol at 100 ?C Density of water 0.958
g/mL (at 100 ?C ) Molar mass of water 18.02
g/mol
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Vapor Pressure
Figure 13.15 Vapor Pressure Consider the
dynamic equilibrium that exists when liquid
ethanol is in contact with its vapor (gas) in a
closed container Vapor pressure is a function of
temperature (vapor pressure increases with
increasing temperature) and depends on the
intermolecular forces between molecules. A
substance that experiences weak attractions will
have a higher vapor pressure and will be
volatile.
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Vapor Pressure (2)
Figure 13.16 Vapor Pressure as a function of
temperature for several substances Boiling point
- temperature at which the vapor pressure for a
substance is equal to the external
pressure. Normal boiling point - refers to when
the external pressure equals 1 atm (or 760 mm Hg
or 760 torr) Locate normal boiling points on
Figure 13.16
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Closer Look (pg 529) Clausius-Clapeyron Equation
P vapor pressure ?H heat of vaporization R gas
constant T absolute temperature
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CRITICAL TEMPERATURE and PRESSURE
Critical temperature (Tc) highest temperature at
which a liquid phase can form. Beyond the
critical temperature, the gas can not be
liquefied by compressing.
Critical pressure (Pc) pressure required to
bring about liquefaction at critical temperature.
Critical point refers to the conditions of Tc
and Pc. At the critical point the interface
between liquid and vapor disappears and the
properties of the substance appear as both liquid
and gas.
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CRITICAL TEMPERATURE and PRESSURE (2)
The magnitude of Tc depends on the strength of
the intermolecular forces. See Table 13.5
Critical Temperatures and Pressures for Common
Compounds
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Surface Tension and Capillary Action
Surface tension - the energy required to break
through the surface of a liquid. Figure 13.19
Capillary action Adhesive versus cohesive
forces Meniscus shape for water and Hg
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11.3 Properties of Some Liquids
Viscosity the resistance of a liquid to flow
The more viscous that a liquid is, the thicker
and more syrup-like that it is.
Viscosity decreases as temperature increases.
Viscosity increases as the strength of
intermolecular forces increase.
Comparison of SAE 40 and SAE 10 motor oils.
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Motor Oilhttp//www.chevron.com/prodserv/nafl/aut
o/content/motoroils.shtm
What to Look for on a Motor Oil LabelThe symbol
at left is referred to as the "API donut." It
gives you three pieces of information. API
(American Petroleum Institute) Service Rating
This two-letter classification identifies the
vehicle fuel type and quality level of the motor
oil. The first letter indicates the vehicle fuel
type that the oil is designed for. Ratings that
begin with an "S" are intended for gasoline
engines. Ratings that begin with a "C" are for
diesel engine. The second letter designates the
quality level of the motor oil. The higher the
letter, the more advanced the oil and the more
protection it offers your engine. An SJ oil can
be used in any engine requiring an SB, SG, SH,
etc. oil.
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Motor Oilhttp//www.chevron.com/prodserv/nafl/aut
o/content/motoroils.shtm
SAE (Society of Automotive Engineers) Viscosity
GradeViscosity is a measure of an oil's
thickness, or resistance to flow. Lower numbers
indicate thinner oil and higher numbers indicate
thicker oil. There are two types of motor oils,
single grade and multi-grade. Multigrade oil such
as a 10W-30, are designed to have the viscosity
of an SAE 10W oil at cold temperatures combined
with the viscosity of an SAE 30 oil at engine
operating temperatures. The "W" or "Winter"
designation indicates that the oil meets
viscosity requirements for low temperatures
(below 30 F).
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Phase Diagrams
Figure 13.35 Phase diagram for water Figure
13.36 Phase diagram for CO2
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11.7 Structures of Solids
Crystalline solids vs Amorphous solids
Figure 11.30 Crystalline SiO2 (quartz) vs
Amorphous SiO2 (glass)
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11.8 Bonding in Solids
Table 11.7 Overview of Four Types
Molecular
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-95
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80 111 182
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Fatty Acids
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COLOR TEST
BLUE
GREEN
RED
YELLOW
PURPLE