Download CHM 103 Lecture 11 S07

Announcements & Agenda (02/02/07)
Quiz Today!!!
Exam NEXT FRIDAY!!!
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Electron
Group
Covers Ch 11-5
Intermolecular Forces (Notes + bits & pieces of Ch 6)
Ch 7.17.1-7.3
CHM 103 Lab
Today
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Last Time: Molecular Shapes
The Mole (5.5(5.5-5.8)
Reactions Types (Especially Redox Rxns)
Rxns) (5.3, 5.4)
Energy of Chemical Reactions (5.9)
Bonded Lone Bond
Molecular
Atoms Pairs Angles Shape
Example
4
4
0
109
tetrahedral CH4
4
3
1
~109
Pyramidal NH3
4
2
2
~109
Bent
H2O
Copyright © 2005 by Pearson Education, Inc.
Publishing as Benjamin Cummings
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Last Time: Polar Molecules
• contain polar bonds.
• have a separation of positive and negative
charge called a dipole indicated with δ+ and δ-.
Chapter 5!!!
Chemical Reactions
• have dipoles that do not cancel!
δ+ δ-
••
H–Cl
H—N—H
dipole
H
dipoles do not
cancel
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Last Time: Conservation of Mass
Revisited – Balanced Reactions (Ch 5)
24 Good Practice Problems (Ch 5)
5.01, 5.05, 5.07, 5.11, 5.13, 5.17,
5.25, 5.27, 5.33, 5.37, 5.41, 5.47,
5.57, 5.69, 5.73, 5.75, 5.79, 5.81,
5.83, 5.85, 5.91, 5.93, 5.95, 5.97
In a balanced
chemical
reaction
• atoms are not
gained or lost.
• the # of reactant
atoms is equal to
the number of
product atoms.
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Steps in Balancing an Equation
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Equations with Polyatomic Ions
To balance the following equation,
Fe3O4(s) + H2(g) Æ Fe(s
Fe(s) + H2O(l
O(l)
• work on one element at a time.
• use only coefficients in front of formulas.
• do not change any subscripts.
Fe:
Fe3O4(s) + H2(g) Æ 3Fe(
3Fe(s) + H2O(l
O(l)
O:
Fe3O4(s) + H2(g)
Æ 3Fe(s
3Fe(s)
+ 4H2O(l)
H:
Fe3O4(s) + 4H2(g) Æ 3Fe(s
3Fe(s)
+ 4H2O(l
O(l)
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The “mole”…. Thinking about
reactions on a realreal-world scale!
Balancing with Polyatomic Ions
MgCl2(aq)
aq) + Na3PO4(aq)
aq) Æ NaCl(aq
NaCl(aq)) + Mg3(PO4)2(s)
ƒ 1 mole is:
Balance PO43- as a unit
MgCl2(aq)
aq) + 2Na3PO4(aq)
aq) Æ NaCl(aq
NaCl(aq)) + Mg3(PO4)2(s)
2 PO43=
2 PO43-
ƒ
ƒ
Balance Mg and Cl
3MgCl2(aq)
aq) + 2Na3PO4(aq)
aq) Æ 6NaCl(aq
NaCl(aq)) + Mg3(PO4)2(s)
3 Mg2+
=
3 Mg2+
+
6 Na
=
6 Na+
6 Cl
=
6 Cl-
a collection of stuff that equals the # of atoms
present in exactly 12.000 g of 12C (6.022 × 1023
atoms)
always 6.022 × 1023 somethings (Avogodro’s #, NA)
ƒ New term: Molar Mass (MM)
ƒ
the mass of 1 mol of an element/compound in gms.
ƒ
e.g. the MM of 12C is 12.000 g/mol
ƒ
b/c 1 mol is defined as 6.022 × 1023 atoms, the MM
for any element can be determined
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Collection Terms
Some OneOne-mole Quantities
One-Mole Quantities
A collection term states
a specific number of items.
• 1 dozen donuts
= 12 donuts
• 1 ream of paper
= 500 sheets
• 1 case
= 24 cans
32.1 g
55.9 g
58.5 g
294.2 g
342.2 g
Copyright © 2005 by Pearson Education, Inc.
Publishing as Benjamin Cummings
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Using Avogadro’s Number
Subscripts and Moles
Avogadro’s number is used to convert
particles of a substance to moles.
The subscripts in a formula show
• the relationship of atoms in the formula.
• the moles of each element in 1 mole of compound.
How many moles of CO2 are in
2.50 x 1024 molecules CO2?
2.50 x 1024 molecules CO2 x
Glucose
C6H12O6
1 mole CO2
6.02 x 1023 molecules CO2
In 1 molecule: 6 atoms C 12 atoms H
6 atoms O
In 1 mole:
6 mole C 12 mole H 6 mole O
= 4.15 mole CO2
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Molar Mass
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Molar Mass from Periodic Table
Molar mass is the
atomic mass
expressed in grams.
• is the mass of one
mole of an element
or compound.
• is the atomic mass
expressed in grams.
Remember atomic
masses???
1 mole Ag
= 107.9 g
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1 mole C
= 12.01 g
1 mole S
= 32.07 g
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Determining the Molar Mass…
Putting the mole to work in
chemical reactions!
1S
SO2
2O
SO2
32.07 g/mol
+ 2 x 16.00 g/mol
64.07 g/mol
For any molecule
molecular mass = Σ all atomic masses
1 mole SO2 = 64.07 g SO2
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Reading Equations In Moles
Calculations Using Molar Mass
Consider the following equation:
4 Fe(s
+ 3 O2(g)
Fe(s)
Molar mass factors are used to convert between the
grams of a substance and the number of moles.
Grams
Molar mass factor
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2 Fe2O3(s)
This equation can be read in “moles” by placing
the
word “moles
“moles”” between each coefficient and
formula.
Moles
4 moles Fe + 3 moles O2
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2 moles Fe2O3
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Steps in Finding the Moles and
Masses in a Chemical Reaction
Calculating the Mass of a Reactant
The reaction between H2 and O2 produces 13.1 g water.
How many grams of O2 reacted?
2 H2(g)
+ O2(g)
2 H2O (g)
?g
13.1 g
The plan and factors would be
g H2O
mole H2O
mole O2
g O2
molar
molemole-mole
molar
mass H2O
factor
mass O2
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Several Types of Reactions (5.3)
Calculating the Mass of a Reactant
Chemical reactions can be classified as:
The setup would be:
• combination reactions.
• decomposition reactions.
13.1 g H2O x 1 mole H2O x 1 mole O2 x 32.0 g O2
18.0 g H2O
2 moles H2O 1 mole O2
molar
molemole-mole
molar
mass H2O
factor
mass O2
• single replacement reactions.
• double replacement reactions.
Don’t stress about these too much; be able to
recognize the different flavors (see suggested
problems)
= 11.6 g O2
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Oxidation-Reduction Reactions (5.4)
Electron Loss and Gain
An oxidationoxidation-reduction reaction
An oxidationoxidation-reduction reaction
• provides us with energy from food.
• provides electrical energy in
batteries.
• occurs when iron rusts.
• transfers electrons from one reactant to another.
4Fe(s
4Fe(s) + 3O2(g)
• loses electrons in oxidation.
Zn(s
Zn(s)
(LEO)
Zn2+(aq)
aq) + 2e- (loss of e-)
• gains electrons in reduction.
(GER)
Cu(s
Cu2+(aq)
aq) + 2eCu(s) (gain of e-)
2Fe2O3(s)
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Oxidation and Reduction
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Writing Oxidation & Reduction Reactions
Write the separate oxidation and reduction reactions
for the following equation.
2Cs(s
2Cs(s) + F2(g)
2CsF(s
2CsF(s)
A cesium atom loses an electron to form cesium ion.
oxidation
Cs(s
Cs+(s) + 1e−
Cs(s)
Fluorine atoms gain electrons to form fluoride ions.
2F−(s)
reduction
F2(s) + 2e27
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Collision Theory of Reactions
Cu and Ag1+
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.
Cu(s)
Orange metal
Ag1+(aq) + 2eColorless
Cu2+(aq) + 2eBlue
Ag(s)
Silver
oxidation
reduction
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Publishing as Benjamin Cummings
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Activation Energy
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Exothermic Reactions
• The activation
energy is the
minimum energy
needed for a
reaction to take
place.
• heat is released.
• the energy of the
products is less than
the energy of the
reactants.
• heat is a product.
• When a collision
provides energy
equal to or
greater than the
activation energy,
product can form.
C(s) + 2 H2(g)
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CH4(g) + 18 kcal
Copyright © 2005 by Pearson Education, Inc.
Publishing as Benjamin Cummings
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Endothermic Reactions
Summary
Reaction
Energy
Heat
Type
Change
in Reaction
Endothermic Heat absorbed
Reactant
• Heat is absorbed.
• The energy of the
products is greater
than the energy of the
reactants.
• Heat is a reactant
(added).
Exothermic
Heat released
Product
Copyright © 2005 by Pearson Education, Inc.
Publishing as Benjamin Cummings
N2(g) + O2 (g) + 43.3 kcal
2NO(g)
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Rate of Reaction
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Reaction Rate and Catalysts
A catalyst
• increases the
rate of a
reaction.
• lowers the
energy of
activation.
• is not used up
during the
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.
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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.
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