Oxidation-Reduction Reactions Chemistry Worksheet Page 15
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6.3 Types of Chemical Reactions
e
6.2 - Combustion Reactions
xerCise
Write balanced equations for the complete combustion of (a) C
H
(g),
O
8
bjeCtive
4
10
(b) C
H
OH(l ), and (c) C
H
SH(l ).
3
7
4
9
If there is insufficient oxygen to burn a carbon‑containing compound completely,
the incomplete combustion converts some of the carbon into carbon monoxide, CO.
Because the combustion of gasoline in a car’s engine is not complete, the exhaust that
leaves the engine contains both carbon dioxide and carbon monoxide. However, before
this exhaust escapes out the tail pipe, it passes through a catalytic converter, which
further oxidizes much of the carbon monoxide to carbon dioxide. See the Special Topic
6.2: Air Pollution and Catalytic Converters.
Air Pollution and Catalytic Converters
S
T
PECIAL
OPIC 6.2
When gasoline, which is a mixture of hydrocarbons, burns
and some transition metal oxides, such as V
O
, CuO,
2
5
in the cylinders of a car engine, the primary products are
and Cr
O
, will speed up oxidation‑reduction reactions.
2
3
carbon dioxide and water. Unfortunately, the hydrocarbons
An automobile’s catalytic converter contains tiny beads
are not burned completely, so the exhaust leaving the
coated with a mixture of transition metals and transition
cylinders also contains some unburned hydrocarbons and
metal oxides. When the exhaust passes over these beads, the
some carbon monoxide, which are serious pollutants.
oxidation of CO to CO
and the conversion of unburned
2
When the unburned hydrocarbon molecules escape into the
hydrocarbons to CO
and H
O are both promoted.
2
2
atmosphere, they combine with other substances to form eye
The conversion of CO to CO
and of unburned
2
irritants and other problematic compounds.
hydrocarbons to CO
and H
O is very slow at normal
2
2
Carbon monoxide is a colorless, odorless, and poisonous
temperatures, but it takes place quite rapidly at temperatures
around 600 °F. This means that the removal of the CO and
gas. When inhaled, it deprives the body of oxygen.
Normally, hemoglobin molecules in the blood carry oxygen
hydrocarbon pollutants does not take place efficiently when
throughout the body, but when carbon monoxide is
you first start your engine. The pollutants released when a
present, it combines with hemoglobin and prevents oxygen
car is first started are called “cold‑start emissions.” Recent
from doing so. As little as 0.001% CO in air can lead to
research has focused on developing a way to insulate the
headache, dizziness, and nausea. Concentrations of 0.1%
catalytic converter so it retains its heat even when the car
can cause death.
is not running. Some of the prototypes can maintain their
Catalytic converters in automobile exhaust systems were
operating temperatures for almost a day while the engine
developed to remove some of the carbon monoxide and
is shut off. With these new, insulated catalytic converters
unburned hydrocarbons from automobile exhaust. A catalyst
installed in most cars, cold‑start emissions could be reduced
is any substance that speeds a chemical reaction without
by at least 50%. This could have a significant effect on air
being permanently altered itself. Some of the transition
pollution.
metals, such as platinum, palladium, iridium, and rhodium,
Out through
exhaust pipe:
In from engine:
CO
2
CO
H
O
2
unburned hydrocarbons
less CO
Calalytic converter
less unburned hydrocarbons
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