Chemistry and
the Environment
Learning Objectives
a. The environment consists of the lithosphere, the
atmosphere, and the hydrosphere.
b. The lithosphere serves as the source for raw
materials and energy resources such as fossil
fuels.
c. Depletion of traditional fuel sources is leading to
the need for alternative/renewable fuels.
d. Solid waste disposal is a growing burden on the
lithosphere.
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Learning Objectives (cont)
e. The atmosphere is suffering from increased
levels of pollutants.
f. Increasing atmospheric CO2 levels have been
linked to global warming through an
enhancement of the greenhouse effect.
g. The Earth’s sunscreen, the ozone layer, has been
damaged by chlorofluorocarbons.
h. During the hydrologic cycle, rainwater can pick
up many pollutants.
i. Acid rain can also result from the reaction of
H2O with atmospheric SO3 and NO2.
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Outline
•
Overview of the Environment
a. Lithosphere
1. The solid surface of the Earth
b. Atmosphere
1. The gaseous layer of air surrounding the Earth
c. Hydrosphere
1. The aqueous part of the Earth
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Outline
•
The Lithosphere
a. Traditional Energy Resources
1. Traditional sources of energy have included biomass
and fossil fuels.
2. More recently, nuclear power has become an option.
3. Supplies of fossil fuels and uranium are limited.
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Evolution of fuel use
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Composition and
Energy Content of Various Fuels
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Global Reserves of Fuels
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Carbon and
Heat Content by Type of Coal
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Coal mining often
leaves environmental disaster in its wake
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The
refining and separation process
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Outline
•
The Lithosphere (cont)
b. Alternative Sources of Energy
1. Depletion of traditional sources of energy such as
petroleum has led to the development of alternative
sources of energy.
2. Renewable energy sources can be replenished on a
short time scale; e.g., solar power and biomass.
3. Example: photovoltaic cells (PVCs), which convert
solar energy into electricity.
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Schematic of
a “pressurized water” type of nuclear reactor
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Different
types of semiconductors
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Photovoltaic Cells
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Outline
•
Lithosphere (cont)
b. Alternative Energy Sources (cont)
4. Fuel cells generate electricity through an
oxidation-reduction reaction for which the
reactants are constantly supplied.
5. An example is the Proton Exchange Membrane
(PEM) fuel cell based on the following reaction:
2 H2 + O2
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2 H2O + energy
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In a PEM fuel
cell, H2 is split into H+ and electrons
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Outline
•
The Lithosphere (cont)
c. Land Pollution
1. Solid waste disposal is a growing problem.
2. The Environmental Protection Agency (EPA)
recommends that we “reduce, reuse, and recycle.”
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Solid Waste
Generated by Americans in 2003
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Composting
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Municipal solid
waste recycling rates, 1960-2003
Source: EPA
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The Atmosphere
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The atmosphere is divided into five layers. It is
thickest near the surface and thins out with height
until it eventually merges with space.
1) The troposphere is the first layer above the surface and
contains half of the Earth's atmosphere, which we breathe.
Weather occurs in this layer.
2) Many jet aircraft fly in the stratosphere because it is very
stable. Also, the ozone layer absorbs harmful rays from the
Sun.
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Atmosphere, continued
3) Meteors or rock fragments burn up in the mesosphere.
4) The thermosphere is a layer with auroras. It is also where
the space shuttle orbits.
5) The atmosphere merges into space in the extremely thin
exosphere. This is the upper limit of our atmosphere.
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Composition of Dry Air at Sea Level
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Outline
•
The Atmosphere
a. The Nitrogen Cycle
1. The atmosphere at sea level is comprised of 78% N2
and 21% O2.
2. The nitrogen cycle is the exchange of nitrogen atoms
between the living and non-living parts of the
environment.
3. During nitrogen fixation, atoms from atmospheric N2
are incorporated into biologically useful nitrogencontaining molecules.
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The Nitrogen Cycle
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Nitrogen-Fixation Reactions
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Outline
•
The Atmosphere (cont)
b. Air Pollutants
1. Pollutants (chemicals in the wrong place at the
wrong concentration) can occur naturally or
from human activity.
2. EPA’s six major air pollutants are SO2,
particulate matter (PM), CO, NOx, O3, and Pb.
3. Depending on atmospheric conditions, pollution
can result in industrial smog or photochemical
smog.
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EPA’s Principal (Primary) Air Pollutants
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Secondary pollutants are formed in the
atmosphere through chemical and
photochemical reactions from the primary
pollutants examples include:
sulfuric acid H2SO4 - can cause respiratory problems
nitrogen dioxide NO2 - gives air a brownish coloration
ozone O3 - colorless gas, has a sweet smell, is an oxidizing
agent, irritates the eyes
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Photochemical Smog
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Sunlight + emissions from
cars and power plants = photochemical smog
N2 + O2  2NO Created by forest fires and the combustion engine
NO + O2  NO2 (a corrosive brown gas)
4 NO2 + 2H2O + O2  4 HNO3 (nitric acid)
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LA. smog:
• requires clear, sunny skies
• NOx + ROG + sunlight --> O3 + NO2
• ROG are reactive organic gases from unburned
gasoline
• NOx are oxides of nitrogen
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Review the Components of
Photochemical Smog
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Industrial Smog
The Source: Burning Coal
Thermal Inversion, in which a blanket of warm air above a low lying layer
of cooler air traps pollutants (SO2, CO, NO2) near the ground.
Production of Sulfur compounds that arise from coal combustion originates
with the release of sulfur within the coal as sulfur dioxide:
S + O2  SO2
Which is a choking gas in its own right, reacts further with atmospheric O2,
which forms sulfur trioxide and combines with water vapor to form sulfuric
acid (H2SO4)
2SO2 + O2  SO3 + H2O  H2SO4
Contributes to acid rain
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A thermal inversion
caused air pollution in London in the 1950s
Thermal inversion
occurs when a
layer of warm air
settles over a
layer of cooler air
that lies near the
ground. The
warm air holds
down the cool air
and prevents
pollutants from
rising and
scattering.
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Air pollution at the
Great Smoky Mountains National Park
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Strategies to Reduce Photochemical Smog
Reduce the number of automobiles on the road
More efficient gasoline-dispensing systems to reduce the release of
hydrocarbons into the atmosphere and catalytic converters to improve the
efficiency of combustion, gas-electric hybrid vehicles, reduced tailpipe
emissions, and fuel efficiency.
Strategies to Reduce Industrial Smog
Cut down on PM and sulfur compounds
Scrubbers that pass emission gases through water and filters that act like
vacuum cleaners and remove sulfur compounds through a chemical
treatment with limestone (CaCO3):
CaCO3(s) + SO2(g)  CaSO3(s) + CO2(g)
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Declining mean blood lead levels for
U.S. children age 5 and younger
Source: EPA
Thomas Midgley
Jr. invented Chlorofluorocarbons
(CFCs) and tetraethyl lead
Credit: Kettering University
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Outline
•
The Atmosphere (cont)
c. Global Climate Change (Global Warming)
1. The greenhouse effect is a warming of the Earth
by a layer of gases that trap the sun’s energy.
2. Human activity appears to be causing an increase
in the amount of atmospheric CO2.
3. Increased atmospheric CO2 appears to be
enhancing the greenhouse effect, leading to an
increase in average global temperatures.
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CO2 levels are
still increasing in the atmosphere
Source: National Oceanic and Atmospheric Administration (NOAA).
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The Earth's
atmosphere acts like the glass in a
greenhouse
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Rising global temperatures
Source: NASA
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Aerosols
can block out solar radiation
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Outline
•
The Atmosphere (cont)
d. Ozone Depletion
1. Ozone forms the Earth’s sunscreen.
2. Chlorofluorocarbons, formerly used as
propellants and refrigerants, break down in the
upper atmosphere to form free radicals that
degrade the ozone layer.
CF2Cl2 + UV light
Cl• + O3
ClO • + O
CF2Cl + Cl•
ClO • + O2
Cl• + O2
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Ozone hole
over Antarctica, October 1979
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Ozone hole
over Antarctica, October 1986
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Ozone hole
over Antarctica, October 2005
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Outline
•
The Hydrosphere
a. Hydrologic Cycle
1. Movement of water between the atmosphere,
the lithosphere, and the hydrosphere
2. During the hydrologic cycle, water may pick up
many pollutants.
3. An example is acid rain (pH < 5.6), resulting
from formation of H2SO4 and HNO3 when
water reacts with atmospheric combustion
products SO2 and NO2.
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Average
Daily Water Use per American
Source: Data from the American Water Works Association.
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Hydrologic Cycle
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Hard-water
deposits inside pipes and kettles
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EPA's
Permissible Mineral Levels in Water
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Ion-exchange
columns for removing Ca2+ and Mg2+
ions
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Handheld water
purifier
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Removal of both
biological and chemical
contaminants
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Possible sources of contamination in the
hydrologic cycle
Water pollution
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Acid rain is
most severe in the Mid-Atlantic states
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Acid Rain
Acid rain is when the rain has a pH of 5.6 or lower due to the presence of
atmospheric carbon dioxide, which reacts with water to form dissolved
carbonic acid (H2CO3).
CO2 + H2O  H2CO3
SO2 further reacts with atmospheric O2, which forms sulfur trioxide and
combines with water vapor to form sulfuric acid (H2SO4)
2SO2 + O2  SO3 + H2O  H2SO4
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The Effect of Acid Rain on calcium carbonate over time
Picture
taken
before acid
rain at the
Field
Museum in
Chicago in
1920
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Picture
taken after
acid rain
at the
Field
Museum
in Chicago
in 1990
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Erosion
increases in the absence of vegetation
Credit: Alamy
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A healthy lake (top)
and one that is suffering from eutrophication
Eutrophication occurs when a
body of water is rich in
nutrients that lead to an
explosion of vegetation and
algae at the expense of other
aquatic life.
Algae formed at the surface of the lake
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An oiled bird
after the Exxon Valdez accident
Credit: AP/Wide World Photos
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