Announcements & Agenda (02/02/07)
Will post these later today 
Pick up quizzes (Ave = 7.1/10)
Exam @ 11 am this Friday
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Review Wed @ 5 pm, Room TBA
Covers Ch 1-5 +Intermolecular Forces (Notes) + Lab
WILL NOT include Ch 7 except the notes from today
Today
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Redox Rxns (5.3, 5.4)
Energy of Chemical Reactions (5.9)
Intermolecular Forces (Notes: Will be on Exam)
1
Last Time: Mass is Conserved in Chemical
Reactions but Need Mole to Solve Problems
2 moles Ag + 1 moles S =
1 mole Ag2S
2 (107.9 g) + 1(32.1 g) = 1 (247.9 g)
247.9 g reactants = 247.9 g product
2
Take home message: Why the mole is
so important in chemistry.
• It is just a number (a quantity) of atoms or
molecules that allows to think about reactions
on a macroscopic scale
 The molecular picture of matter
• When trying to determine how much “stuff” is
needed or produced in a chemical reaction,
we find that the balanced equation
 works in “moles”
 doesn’t work in mass
3
Last Time: Several Types of Reactions (5.3)
Chemical reactions can be classified as:
• combination reactions.
• decomposition reactions.
• single replacement reactions.
• double replacement reactions.
Don’t stress about these too much; be able to
recognize the different flavors (see suggested
problems)
4
Oxidation-Reduction Reactions (5.4)
An oxidation-reduction reaction
• provides us with energy from food.
• provides electrical energy in
batteries.
• occurs when iron rusts.
4Fe(s) + 3O2(g)
2Fe2O3(s)
5
Electron Loss and Gain
An oxidation-reduction reaction
• transfers electrons from one reactant to another.
• loses electrons in oxidation.
Zn(s)
(LEO)
Zn2+(aq) + 2e- (loss of e-)
• gains electrons in reduction.
(GER)
Cu2+(aq) + 2eCu(s) (gain of e-)
6
Oxidation and Reduction
7
Writing Oxidation & Reduction Reactions
Write the separate oxidation and reduction reactions
for the following equation.
2Cs(s) + F2(g)
2CsF(s)
A cesium atom loses an electron to form cesium ion.
Cs(s)
Cs+(s) + 1e−
oxidation
Fluorine atoms gain electrons to form fluoride ions.
F2(s) + 2e2F−(s)
reduction
8
Cu and Ag1+
COOL DEMO!
Cu(s)
Orange metal
Ag1+(aq) + 2eColorless
Cu2+(aq) + 2eBlue
Ag(s)
Silver
oxidation
reduction
9
Collision Theory of Reactions (5.9)
A chemical reaction occurs when
• collisions between molecules have sufficient
energy to break the bonds in the reactants.
• bonds between atoms of the reactants (N2 and
O2) are broken and new bonds (NO) can form.
Copyright © 2005 by Pearson Education, Inc.
Publishing as Benjamin Cummings
10
Activation Energy
• The activation
energy is the
minimum energy
needed for a
reaction to take
place.
• When a collision
provides energy
equal to or
greater than the
activation energy,
product can form.
11
Exothermic Reactions
• heat is released.
• the energy of the
products is less than
the energy of the
reactants.
• heat is a product.
C(s) + 2 H2(g)
CH4(g) + 18 kcal
Copyright © 2005 by Pearson Education, Inc.
Publishing as Benjamin Cummings
12
Endothermic Reactions
• Heat is absorbed.
• The energy of the
products is greater
than the energy of the
reactants.
• Heat is a reactant
(added).
Copyright © 2005 by Pearson Education, Inc.
Publishing as Benjamin Cummings
N2(g) + O2 (g) + 43.3 kcal
2NO(g)
13
Summary
Reaction
Type
Endothermic
Energy
Heat
Change
in Reaction
Heat absorbed
Reactant
Exothermic
Heat released
Product
14
Rate of Reaction
• is the speed at which reactant is used up.
• is the speed at which product forms.
• increases when temperature rises because
reacting molecules move faster providing
more colliding molecules with energy of
activation.
15
Reaction Rate and Catalysts
A catalyst
• increases the
rate of a
reaction.
• lowers the
energy of
activation.
• is not used up
during the
reaction.
16
Learning Check
State the effect of each on the rate of reaction as:
1) increases
2) decreases
3) no change
A. increasing the temperature.
B. removing some of the reactants.
C. adding a catalyst.
D. placing the reaction flask in ice.
E. increasing the concentration of one of the
reactants.
17
Intermolecular Forces (Notes Only)
Inter-
vs.
Latin: Between
molecules
IntraAmong
molecules
Dispersion Forces
Dipolar Forces
Hydrogen Bonding
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Phases of elements at STP
Only 11 elements are gases
Why? Intermolecular forces: forces of attraction
between molecules which result in liquids and
solids
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On what do the intermolecular forces depend?
Molar mass
Polarity
20
Melting & Boiling Points
Both are indicators of the strengths of
intermolecular forces:
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freezing point (fp): the temperature at which a solid &
liquid coexist at equilibrium under ‘normal’ pressures
boiling point (bp): the temperature at which a liquid &
vapor coexist at equilibrium under ‘normal’ pressures
Exam Questions: Rank Compounds by BPs OR
Explain why one compound has a higher bp/mp than
another bases on IM forces
21
Intermolecular forces:
Actually all the same force!
Electrostatic
Dispersion Forces:
From polarizability of atoms
Dipolar Forces:
From permanent dipole moments
Hydrogen-bonding:
Special case of dipolar forces
22
… but remember that intermolecular
forces are weaker than covalent or
ionic bonds!!!!
23
1. Dispersion Forces
Found in all molecular substances
Electrostatic in nature; arise from attractions involving
induced dipoles.
Ask me about
Geckos?
Magnitude depends on how easy it is to polarize the
electron cloud of a molecule.
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larger molecules have larger polarizability.
24
p. 92
Polarizability increases….
with increasing MM
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1. Dispersion Forces:
Larger shapes are more polarizable
Higher boiling point 
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Intermolecular Forces
Intermolecular forces not only hold small molecules in
liquids and solids together, but also drive very large
molecules to bind to each other - this is necessary for
cell functions.
(Turn on
a gene)
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1. More on London Dispersion Forces
Individually, dispersion (van der Waal’s) forces are
thought of as very weak. However, these forces
between large molecules can be very strong - e.g.
motor oil, vaseline are entirely non-polar molecules.
In water “hydrophobic bonding” drives large non-polar
molecules or parts of molecules together.
Sodium dodecyl sulfate (= sodium lauryl sulfate)
CH3-CH2 -CH2 -CH2 -CH2 -CH2 -CH2 -CH2 -CH2 -CH2 -CH2 -CH2-SO3Nonpolar Hydrophobic = “water-hating”
Ionic
Hydrophillic =
“water loving”
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2. Dipolar Forces
Occur when one polar molecule encounters
another polar molecule.
The positive ends will be attracted to the
negative ends.
Dipolar forces are typically stronger than
dispersion forces.
Dipolar forces increase with an increase in the
polarity of the molecule.
NOTE: Ion-dipole forces stronger than dipolar
forces.
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2. Dipolar Forces:
permanent dipole monents….
Higher boiling point 
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Example
Explain the trend in bp’s: butane (0°C), methyl ethyl
ether (8°C) and acetone (56°C).
31
3. Hydrogen Bonding
• Special case of dipole-dipole forces.
• By experiments: boiling points of compounds with
H-F, H-O, and H-N bonds are abnormally high.
• Intermolecular forces are abnormally strong.
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Hydrogen Bonding
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Hydrogen Bonding
Hydrogen Bonding
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p. 94
Electronegative atom with lone pair
dd+
Electron deficient H atom
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