CHEM 1B: General Chemistry
Extra Chapter:
Environmental
Chemistry
Instructor: Dr. Orlando E. Raola
Santa Rosa Junior College
Outline
• Atmosphere
General
• physical structure
• chemical composition
Outer Atmosphere
• ozone - photochem,
Troposphere
• sulfur, acid rain
• CO
• NOx, smog
• CO2, H2O
• Climate
• Water
Oceans
• composition, desalination
Freshwater
• oxygen, water treatment
• “Green Chemistry”
• principles
• examples
Atmosphere
• Temperature varies
greatly with altitude.
• The profile makes a
Z-shape from
mesosphere to the
ground.
Atmosphere
Pressure is highest at
the surface and
decreases with
height.
Fluctuations in
pressure are a
driving force of
weather.
Radiation
{
Aurora
Formed
here
The atmosphere is
the first line of
defense against
radiation from the
Sun.
Composition of the Atmosphere
• The composition of
gases in the
atmosphere is not
uniform.
• Lighter gases tend to
rise to the top.
Gases are measured in ppm volume (µL/L),
which is directly proportional to mole
fraction.
Composition of the Atmosphere
• Near the Earth’s
surface, about 99% of
the atmosphere is
composed of nitrogen
and oxygen.
• Oxygen has a much
lower bond enthalpy
than nitrogen, and is
therefore more reactive.
Number of photons
Outer Atmosphere
Wavelength, m
Energy
• The Sun emits
radiation across the
electromagnetic
spectrum.
• Light in the
ultraviolet region has
enough energy to
break chemical
bonds.
Photochemistry =
1. Photodisociation
2. Photoionization
• Oxygen in the upper atmosphere
absorbs much of the solar radiation
before it reaches the lower atmosphere:
O2 + h  2 O
• These bonds break homolytically.
SAMPLE EXERCISE 18.2 Calculating the Wavelength Required to Break a Bond
What is the maximum wavelength of light, in nanometers, that has enough energy per
photon to dissociate the O2 molecule which has a dissociation energy of 495 kJ/mol?
SAMPLE EXERCISE 18.2 Calculating the Wavelength Required to Break a Bond
What is the maximum wavelength of light, in nanometers, that has enough energy per
photon to dissociate the O2 molecule which has a dissociation energy of 495 kJ/mol?
Solution
Analyze: We are asked to determine the wavelength of a photon that has just sufficient energy
to break the double bond in O2.
Plan: We first need to calculate the energy required to break the double bond in one molecule,
then find the wavelength of a photon of this energy.
SAMPLE EXERCISE 18.2 Calculating the Wavelength Required to Break a Bond
What is the maximum wavelength of light, in nanometers, that has enough energy per
photon to dissociate the O2 molecule which has a dissociation energy of 495 kJ/mol?
Solution
Analyze: We are asked to determine the wavelength of a photon that has just sufficient energy
to break the double bond in O2.
Plan: We first need to calculate the energy required to break the double bond in one molecule,
then find the wavelength of a photon of this energy.
Solve: The dissociation energy of O2 is 495 kJ/mol. Using this value and Avogadro’s number,
we can calculate the amount of energy needed to break the bond in a single O2 molecule:
We next use the Planck relationship, E = h, to calculate the frequency, , of a photon that has this
amount of energy:
Finally, we use the relationship between the frequency and wavelength of light (Section 6.1) to
calculate the wavelength of the light:
Photochemistry =
1. Photodisociation
2. Photoionization
• Short wavelength radiation (ionizing radiation)
causes electrons to be knocked out of molecules
in the upper atmosphere; very little of this radiation
reaches the Earth’s surface.
• The presence of these ions makes long-range
radio communication possible.
Ozone
• Ozone absorbs much of the radiation
between 240 and 310 nm.
• It forms from reaction of molecular oxygen
with the oxygen atoms produced in the upper
atmosphere by photodissociation (< 242 nm).
O + O2  O3
Ozone Depletion
In 1974 Rowland and Molina (Nobel Prize,
1995) discovered that chlorine from
chlorofluorocarbons (CFCs) may be
depleting the supply of ozone in the upper
atmosphere.
Chlorofluorocarbons
CFCs were used for years as aerosol
propellants and refrigerants.
Mostly = CFCl3, CF2Cl2.
They are not water soluble (so they do not
get washed out of the atmosphere by
rain)
and are quite unreactive (so they are not
degraded naturally).
Chlorofluorocarbons
• The C—Cl bond is easily broken,
though, when the molecule absorbs
radiation with a wavelength between
190 and 225 nm.
• The chlorine atoms formed react with
ozone:
Cl + O3  ClO + O2
Movie…
Chlorofluorocarbons
In spite of the fact that the use of CFCs
in now banned in over 100 countries,
ozone depletion will continue for some
time because of the tremendously
unreactive nature of CFCs.
Troposphere
Although the troposphere is made up almost
entirely of nitrogen and oxygen, other gases
present in relatively small amounts still have
a profound effect on the troposphere.
Sulfur
• Sulfur dioxide is a byproduct of the burning
of coal or oil.
• It reacts with moisture
in the air to form
sulfuric acid.
• It is primarily
responsible for acid
rain.
Sulfur
• High acidity in rainfall
causes corrosion in building
materials.
• Marble and limestone
(calcium carbonate) react
with the acid; structures
made from them erode.
Sulfur
• SO2 can be
removed by
injecting powdered
limestone which is
converted to
calcium oxide.
• The CaO reacts
with SO2 to form a
precipitate of
calcium sulfite.
This process = “scrubbing”
Carbon Monoxide
• Carbon monoxide
binds preferentially to
the iron in red blood
cells.
• Exposure to CO can
lower O2 levels to the
point of causing loss
of consciousness and
death.
Carbon Monoxide
• Products that can
produce carbon
monoxide must contain
warning labels.
• Carbon monoxide is
colorless and odorless,
so detectors are a good
idea.
Nitrogen Oxides
• What we recognize as
smog, that brownish
gas that hangs above
large cities like Los
Angeles, is primarily
nitrogen dioxide, NO2.
• It forms from the
oxidation of nitric oxide,
NO, a component of
car exhaust.
Photochemical Smog
Smog also contains
ozone, carbon
monoxide,
hydrocarbons, and
particles.
Water Vapor and Carbon Dioxide
• Gases in the atmosphere form an
insulating blanket that causes the
Earth’s thermal consistency.
• Two of the most important such
gases are carbon dioxide and
water vapor.
Water Vapor and Carbon Dioxide
• This blanketing effect is
known as the
“greenhouse effect.”
• Water vapor, with its high
specific heat, is a major
factor in this moderating
effect.
• But increasing levels of
CO2 in the atmosphere is
causing an increase in
global temperatures.
Mount Pinatubo
Meelh, 2005.
Oceans
• The vast ocean
contains many
important compounds
and minerals.
• However, the ocean is
a commercial source
only of sodium chloride,
bromine, and
magnesium.
Desalination
• “Water, water
everywhere, and not a
drop to drink.” Seawater
has too high a
concentration of NaCl for
human consumption.
• It can be desalinated
through reverse osmosis.
Reverse Osmosis
• Water naturally flows through a
semipermeable membrane from regions of
higher water concentration to regions of
lower water concentration.
• If pressure is applied, the water can be
forced through a membrane in the opposite
direction, concentrating the pure water.
Water Purification
• Clean, safe fresh water
supplies are of the
utmost importance to
society.
• There are many steps
involved in purifying
water for a municipal
water supply.
Water Purification
• Water goes
through several
filtration steps.
• CaO and
Al2(SO4)3 are
added to aid in the
removal of very
small particles.
Water Purification
• The water is aerated
to increase the
amount of dissolved
oxygen and promote
oxidation of organic
impurities.
• Ozone or chlorine is
used to disinfect the
water before it is sent
out to consumers.
Green Chemistry
• We have become increasingly aware over
the past 30 to 40 years that modern
processes are not always compatible with
maintaining a sustainable environment.
• Promoting chemical processes that are
environmentally friendly is part of the
good stewardship.
Green Chemistry Principles
1. Rather than worry about waste
disposal, it is better to avoid creating
waste in the first place.
2. Try to generate as little waste as
possible, and try to make waste that is
nontoxic.
3. Be energy conscious in designing
syntheses.
Green Chemistry Principles
4. Catalysts that allow the use of safe
chemicals should be employed when
possible.
5. Try to use renewable feedstocks as
raw materials.
6. Try to reduce the amount of solvent
used, and try to use environmentally
friendly solvents.
Solvents
Solvents such as supercritical water and CO2
are great “green” alternatives.
Reagents
• Phosgene, COCl2, is
commonly used as a
starting material for plastic
polymers.
• Phosgene is a highly toxic
substance, and the byproducts of many of its
reactions are undesirable.
A superior
alternative might be
dimethyl carbonate.
Reagents
QuickTime™ and a
TIFF (Uncompressed) decompressor
are needed to see this picture.
Metathesis reaction
Ni mining/sulfide minerals
acid mine drainage
Sulfide minerals = FeS2, ZnS, CuS, (Ni, Fe)9S8
Sulfuric acid
Acid dissolves additional minerals, releasing
metals into the watershed.
Downstream reactions:
QuickTime™ and a
TIFF (Uncompressed) decompressor
are needed to see this picture.
Description: Iron hydroxide precipitate (orange) in a Missouri stream
receiving acid drainage from surface coal mining.
Source: Environmental Contaminants; Status and Trends of the Nations Biological Resources
(Retrieved May 5, 2005)
Credit: D. Hardesty, USGS Columbia Environmental Research Center.