Intermolecular Forces and

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Intermolecular Forces and Liquids and Solids
Chapter 11
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Intermolecular Forces Liquids, Solids, and
Phase Changes
12.1 An Overview of Physical States and Phase
Changes
12.2 Types of Intermolecular Forces
12.3 Properties of the Liquid State
12.4 The Uniqueness of Water
12.5 Phase Changes
12.6 Quantitative Aspects of Phase Changes
12.7 Phase Diagrams
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A phase is a homogeneous part of the system in
contact with other parts of the system but
separated from them by a well-defined boundary.
2 Phases
Solid phase - ice
Liquid phase - water
11.1
4
Intermolecular Forces
Intermolecular forces are attractive forces
between molecules.
Intramolecular forces hold atoms together in a
molecule.

• Intermolecular vs Intramolecular
• 41 kJ to vaporize 1 mole of water (inter)
• 930 kJ to break all O-H bonds in 1 mole of water
  (intra)

Measure of intermolecular force boiling
point melting point DHvap DHfus DHsub
11.2
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Intermolecular Forces
Dipole-Dipole Forces
Attractive forces between polar molecules
11.2
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Intermolecular Forces
Ion-Dipole Forces
Attractive forces between an ion and a polar
molecule
11.2
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Intermolecular Forces
Dispersion Forces
Attractive forces that arise as a result of
temporary dipoles induced in atoms or molecules
ion-induced dipole interaction
dipole-induced dipole interaction
11.2
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Intermolecular Forces
Dispersion Forces Continued
Polarizability is the ease with which the
electron distribution in the atom or molecule can
be distorted.

• Polarizability increases with
• greater number of electrons
• more diffuse electron cloud

11.2
9
What type(s) of intermolecular forces exist
between each of the following molecules?
HBr
HBr is a polar molecule dipole-dipole forces.
There are also dispersion forces between HBr
molecules.
CH4
CH4 is nonpolar dispersion forces.
SO2
SO2 is a polar molecule dipole-dipole forces.
There are also dispersion forces between SO2
molecules.
11.2
10
Intermolecular Forces
Hydrogen Bond
The hydrogen bond is a special dipole-dipole
interaction between they hydrogen atom in a polar
N-H, O-H, or F-H bond and an electronegative O,
N, or F atom.
A B are N, O, or F
11.2
11
Why is the hydrogen bond considered a special
dipole-dipole interaction?
11.2
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Properties of Liquids
Surface tension is the amount of energy required
to stretch or increase the surface of a liquid by
a unit area.
Strong intermolecular forces
High surface tension
11.3
13
Properties of Liquids
Cohesion is the intermolecular attraction between
like molecules
Adhesion is an attraction between unlike molecules
11.3
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Properties of Liquids
Viscosity is a measure of a fluids resistance to
flow.
Strong intermolecular forces
High viscosity
11.3
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Water is a Unique Substance
Density of Water
11.3
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Condensation
Evaporation
11.8
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The equilibrium vapor pressure is the vapor
pressure measured when a dynamic equilibrium
exists between condensation and evaporation
11.8
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Before Evaporation
At Equilibrium
11.8
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Molar heat of vaporization (DHvap) is the energy
required to vaporize 1 mole of a liquid.
P (equilibrium) vapor pressure
T temperature (K)
R gas constant (8.314 J/Kmol)
11.8
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The Clausius-Clapeyron Equation
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Using the Clausius-Clapeyron Equation
SOLUTION
34.90C 308.0K

T2 350K 770C
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The boiling point is the temperature at which the
(equilibrium) vapor pressure of a liquid is equal
to the external pressure.
The normal boiling point is the temperature at
which a liquid boils when the external pressure
is 1 atm.
11.8
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The critical temperature (Tc) is the temperature
above which the gas cannot be made to liquefy, no
matter how great the applied pressure.
The critical pressure (Pc) is the minimum
pressure that must be applied to bring about
liquefaction at the critical temperature.
11.8
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The melting point of a solid or the freezing
point of a liquid is the temperature at which the
solid and liquid phases coexist in equilibrium
Freezing
Melting
11.8
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Molar heat of fusion (DHfus) is the energy
required to melt 1 mole of a solid substance.
11.8
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11.8
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A cooling curve for the conversion of gaseous
water to ice
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Quantitative Aspects of Phase Changes
Within a phase, a change in heat is accompanied
by a change in temperature which is associated
with a change in average Ek as the most probable
speed of the molecules changes.
q (amount)(molar heat capacity)(DT)
During a phase change, a change in heat occurs at
a constant temperature, which is associated with
a change in Ep, as the average distance between
molecules changes.
q (amount)(enthalpy of phase change)
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The specific heat (s) of a substance is the
amount of heat (q) required to raise the
temperature of one gram of the substance by one
degree Celsius.
The heat capacity (C) of a substance is the
amount of heat (q) required to raise the
temperature of a given quantity (m) of the
substance by one degree Celsius.
C ms
Heat (q) absorbed or released
q msDt
q CDt
Dt tfinal - tinitial
6.4
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s of Fe 0.444 J/g 0C
Dt tfinal tinitial 50C 940C -890C
q msDt
869 g x 0.444 J/g 0C x 890C
-34,340 J
6.4
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6.4
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Calculate the amount of energy (in kJ) needed to
heat 346 g of liquid water from 0 oC to 182 oC.
The specific heat of water is 4.184 J/g.oC over
the entire liquid range and the specific heat of
steam is 1.99 J/g.oC. DHvap 40.79 kJ/mol
Step 1 heating water from 0 oC to 100 oC Step
2 evaporating 346 g of water at 100 oC Step 3
heating steam from 100 oC to 180 oC Step 4
qoverall q1 q2 q3
q1 m s.h. Dt
q2 moles of water x DHvap
q3 m s.h. Dt
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Molar heat of sublimation (DHsub) is the energy
required to sublime 1 mole of a solid.
Sublimation
Deposition
DHsub DHfus DHvap
( Hesss Law)
11.8
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A phase diagram summarizes the conditions at
which a substance exists as a solid, liquid, or
gas.
Phase Diagram of Water
11.8
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11.8