Chapter 12a Chemical Reactions
•12-1. Phlogiston
•12-2. Oxygen
•12-3. The Mole
•12-4. Formula Units
•12-5. Exothermic and
Endothermic Reactions
•12-6. Chemical Energy and
Stability
•12-7. Activation Energy
12-1. Phlogiston
Two early German chemists, Johann
Becher and Georg Stahl, developed the
phlogiston hypothesis.
Johann Becher
1635-1682)
Georg Stahl
(1669-1734)
The seventeenth century French chemist
Antoine Lavoisier performed experiments that
rejected the phlogiston hypothesis.
Lavoisier's experiments suggested that when
tin is heated, the white powder formed results
from the tin combining with a gas from the air.
The increase in mass of the powder over the
tin was the mass of the gas.
Lavoisier revolutionized chemistry by basing
his ideas on accurate measurements.
Antoine
Lavoisier
(1743-1794)
The English chemist Joseph Priestley discovered a
gas that Lavoisier later named oxygen
Joseph Priestley
(1733-1804)
When oxygen combines
chemically with another
substance, the process
is called oxidation, and
the substance is said to
be oxidized.
Fig. 12.4-5
A fire can be put out by cooling it with water or
depriving it of oxygen. Burning is the result of
oxygen reacting with other materials.
Rust is caused by
the reaction of
oxygen with iron.
12.3 The Mole
The mole is a number, 6.02 x 1023. When you have a
mole of something you have 6.02 x 1023 of them. When
you have a mole of atoms or molecules you have enough
to see and weigh. The weight of a mole of one type of
atoms is the atomic weight from the periodic table in
grams. The mole allows you to count atoms by weighing.
For example, how many carbon atoms are there in 24
grams of carbon? From the periodic table each mole has
12 grams. So there are 2 moles or 2 x 6.02x1023 atoms of
carbon or 12.04x1023 carbon atoms.
Fig. 12.6
12.3 The Mole Figs. 12.7-8
12.4 Formula Units
To find out how much a mole of molecules weigh you
just add up the atomic weights of the atoms in the
molecule.
How much does one mole of NaOH weigh?
Add the atomic weights of Na, O, and H you get 23 +
16 + 1 = 40 grams. How much does a mole of H2O
weigh?
Add 2 times 1 for H and 16 for O to get 18 grams.
How much does a mole of C3H8 weigh?
(3 x 12) + (8 x 1 ) = 36 + 8 = 44 grams.
Fig. 12.9
C3H8 + 5O2  3CO2 + 4H2O
12.5 Exothermic and Endothermic
Reactions
•Chemical changes that give
off energy are called
exothermic reactions.
•Chemical changes that absorb
energy are called
endothermic reactions.
Fig. 12.10-11
35/97 people
died in 1937
12.6 Chemical Energy and
Stability
The more energy needed to decompose a
substance, the greater the chemical stability of the
substance (with a few exceptions).
Chemical energy is electron potential
energy.
When electrons move to new locations
during an exothermic reaction, some of
their original potential energy is
liberated.
Collision Model
• Molecules must collide in order for a reaction to
occur.
• Rate depends on concentrations of reactants and
temperature.
14
What makes Switzerland unique?
12.7 Activation Energy
Chemical Reactions must go over an energy
hill like a mountain (Swiss Alps).
Catalyst
• A substance that speeds up a reaction without
being consumed or makes a tunnel through the
Activation Energy Hill.
Chlorofluoro
Carbons (CFC’s) are
acting as catalysts
to decompose the
ozone (O3) layer.
The ozone layer is
formed from cosmic
radiation and
protects us from UV
light.
18
O-zone depletion from Antarctica
Depletion is measured by T.O.M.S.
“Total O-zone Mapping Spectrometer”
The below dark shaded are shows the amount of depletion
around the Antarctica
Catalyst
An Amana refrigerator, one
of many appliances that
now use HFC-134a. This
compound is replacing
CFC’s, which lead to the
destruction of atmospheric
ozone.
Enzyme – catalyst in a
biological system
20
Use a catalytic converter to convert the polluting
exhaust gases of burned lead-free gasoline into
harmless gases. Platinum (Pt) is the catalysts
used. Only a small amount is needed.
21
Chapter 12b Chemical Reactions
•12-8. Reaction Rates
•12-9. Other Factors
•12-10. Chemical Equilibrium
•12-11. Altering Chemical
Equilibrium
•12-13. Electrochemical Cells
12-8 What Affects Chemical
Reactions?
•Temperature
•A 10oC rise in temperature approximately doubles the
speed of a chemical reaction occurring at or near room
temperature.
•Concentration and Surface Area
•Catalysts (enzymes)
•A catalyst is a substance that can change the rate of a
chemical reaction without itself being permanently
changed.
12-8 What Affects Chemical
Reactions?
Histamine attacks
are greater when you
are hot. Cooling
down affected areas
can reduce allergy
symptoms.
12-10 Chemical Equilibrium
• A dynamic state where the concentrations of all
reactants and products remain constant.
25
12.10 Chemical Equilibrium
In a chemical equilibrium,
forward and reverse reactions
occur at the same rate; the
concentration of the reactants
and products remain
constant. You can cause the
equilibrium to shift by adding
or removing reactants or
products.
Below CO2 gas is in
equilibrium with the water in
the soda.
12-11 Altering Chemical
Equilibrium
Industrial Application-The Manufacture of
Ammonia
N2(g) + 3H2(g)
2NH3(g)
ΔH = -92.4 kJ mol-1
To increase production how would you manipulate the
equilibrium?
1. Lower Volume
2. Lower Temperature
3. Remove Product
27
Electrolysis (Electroplating)
Steel plated with tin prevents
corrosion and is used in
beverage containers. One
key above has been plated
with copper.
Electrolysis (Electroplating)
More examples
of
electroplating.
• Oxidation–reduction reaction
(redox reaction) – a chemical
reaction involving the transfer
of electrons.
 Oxidation – loss of electrons
 Reduction – gain of electrons
30
http://www.youtube.com/watch?v=Ftw7a5ccubs
Types of Batteries
Electrochemical
cells use oxidationreduction reactions
to produce electric
current.
The Lead Storage
Battery
Types of Batteries
The
Alkaline
Battery
Types of
Batteries
The
Lithium
Battery
Hydrogen Fuel Cell
Hydrogen gas is an excellent fuel produced by the
electrolysis of water.