Transcript Lecture 2

Chemical Reactions
Chapter 10
For Science Fair Judges
Revised instructions!
Submit a list of projects that you judged with
the associated grade-levels. A brief
description of your impression of the projects
would be helpful. (Be in SUB Ballroom by
5:00 PM for dinner and instructions.)
If you are not a judge, you may attend the
Science Expo and write a detailed summary of
at least two projects.
Either is extra-credit points or a lab make-up.
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Types of Chemical Reactions
1) Oxidation-Reduction (Redox)
2) Combination
3) Decomposition
4) Replacement
5) Ion Exchange
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Oxidation-Reduction Reactions
(electron transfer reactions)
Oxidation – an atom loses electrons
Reduction – an atom gains electrons
2 Mg (s) + O2 (g)
2 MgO (s)
O2 is the oxidizing agent (takes electrons and
is reduced)
Mg is the reducing agent (supplies electrons and
is oxidized)
Mg2+O2-
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Fig. 10.9 Example of an oxidizing agent (“chlorine”)
Others:
1) Bleach
2) Hydrogen
peroxide
3) Oxygen
4) Ultraviolet
light
Types of Chemical Reactions
1) Oxidation-Reduction (Redox)
2) Combination
3) Decomposition
4) Replacement
5) Ion Exchange
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Fig. 10.10 Iron combines with oxygen to
form rust (iron oxide)
4 Fe (s) + 3 O2 (g)
2 Fe2O3 (s)
Hydrogen combines with oxygen
to form water (dihydrogen monoxide)
Types of Chemical Reactions
1) Oxidation-Reduction (Redox)
2) Combination
3) Decomposition
4) Replacement
5) Ion Exchange
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Fig. 10.11 Decomposition of Mercury Oxide
heat
2 HgO (s) → 2 Hg (l) + O2 (g)
Decomposition of Hydrogen Peroxide
2 H2O2 (l) → 2 H2O (l) + O2 (g)
(Demo)
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Types of Chemical Reactions
1) Oxidation-Reduction (Redox)
2) Combination
3) Decomposition
4) Replacement
5) Ion Exchange
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Fig. 10.13 Replacement reaction between aluminum
metal and the blue copper chloride solution
2 Al (s) 3 CuCl2 (aq) → 2 AlCl3 (aq) + 3 Cu (s)
Cu
Al
CuCl2
AlCl3
• Replacement reactions take place when a
more active metal gives up electrons to a less
active metal.
• How do we know if a replacement reaction
will take place or not occur?
• Refer to the activity series
• Fig 10.12, p 264
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Fig. 10.12 The activity series for common metals
2NaOH + H2 ↑
2 Na + 2H2O
(Demo)
Zn + 2HCl
ZnCl2 + H2 ↑
(Demo)
Types of Chemical Reactions
1) Oxidation-Reduction (Redox)
2) Combination
3) Decomposition
4) Replacement
5) Ion Exchange
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2 KI + Pb(NO3)2 → PbI2 ↓ + 2 KNO3
Pg 253
PbI2
Ion Exchange Reaction – ions of one compound
react with ions of another compound to form:
(1) a solid (precipitate) or
FeCl3 + 3 NaOH → Fe(OH)3 + 3 NaCl
(2) a gas or (3) water
CaCO3 + 2 HCl → CaCl2 + CO2 ↑ + H2O
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Micro World
atoms & molecules
Macro World
grams
Atomic mass is the mass of an atom in
atomic mass units (u)
By definition:
1 atom 12C “weighs” 12 u
On this scale
1H
= 1.008 u
16O
= 16.00 u
Natural lithium is:
7.42% 6Li (6.015 u)
92.58% 7Li (7.016 u)
Average atomic mass of lithium:
(7.42 · 6.015) + (92.58 · 7.016)
= 6.941 u
100
Average atomic mass (6.941)
mole - the amount of a substance that
contains as many particles as there
are atoms in exactly 12.00 grams of 12C
1 mol = NA = 6.0221367 x 1023
Avogadro’s number (NA)
eggs
Molar mass - the mass of 1 mole of shoes in grams
marbles
atoms
1 mole 12C atoms = 6.022 x 1023 atoms = 12.00 g
1 12C atom = 12.00 u
1 mole 12C atoms = 12.00 g 12C
1 mole lithium atoms = 6.941 g of Li
For any element
atomic mass (u) = molar mass (grams)
One Mole of:
S
C
Hg
Cu
Fe
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Molecular mass (or molecular weight) - the sum of
the atomic masses (in u) in a molecule.
1S
SO2
2O
SO2
32.07 u
+ 2 x 16.00 u
64.07 u
For any molecule
molecular mass (u) = molar mass (grams)
1 molecule SO2 = 64.07 u
1 mole SO2 = 64.07 g SO2
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