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Chapter%2018%20Chemistry%20of%20the%20Environment

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Chemistry, The Central Science, 10th edition Theodore L. Brown; H. Eugene LeMay, Jr.; and Bruce E. Bursten Chapter 18 Chemistry of the Environment – PowerPoint PPT presentation

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Title: Chapter%2018%20Chemistry%20of%20the%20Environment


1
Chapter 18 Chemistry of the Environment
Chemistry, The Central Science, 10th
edition Theodore L. Brown H. Eugene LeMay, Jr.
and Bruce E. Bursten
John D. Bookstaver St. Charles Community
College St. Peters, MO ? 2006, Prentice Hall, Inc.
2
Atmosphere
  • Temperature varies greatly with altitude.
  • However, there is not a linear relationship
    between altitude and temperature.

3
Atmosphere
  • Although the relationship between altitude and
    pressure is not linear, pressure does decrease
    with an increase in altitude.

4
Radiation
  • The atmosphere is the first line of defense
    against radiation from the Sun.

5
Composition of the Atmosphere
  • Because of the great variation in atmospheric
    conditions, the composition of gases in the
    atmosphere is not uniform.
  • Lighter gases tend to rise to the top.

6
Composition of the Atmosphere
  • Near the Earths 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.

7
Outer Atmosphere
  • The Sun emits a wide range of wavelengths of
    radiation.
  • Remember that light in the ultraviolet region has
    enough energy to break chemical bonds.

8
Photodissociation
  • When these bonds break, they do so homolytically.
  • Oxygen in the upper atmosphere absorbs much of
    this radiation before it reaches the lower
    atmosphere
  • O2 h? ??? 2 O

9
Photoionization
  • Shorter wavelength radiation causes electrons to
    be knocked out of molecules in the upper
    atmosphere very little of this radiation reaches
    the Earths surface.
  • The presence of these ions makes long-range radio
    communication possible.

10
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.
  • O O2 ??? O3

11
Ozone Depletion
  • In 1974 Rowland and Molina discovered that
    chlorine from chlorofluorocarbons (CFCs) may be
    depleting the supply of ozone in the upper
    atmosphere by reacting with it.

12
Chlorofluorocarbons
  • CFCs were used for years as aerosol propellants
    and refrigerants.
  • 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).

13
Chlorofluorocarbons
  • The CCl 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

14
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.

15
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.

16
Sulfur
  • Sulfur dioxide is a by-product 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.

17
Sulfur
  • High acidity in rainfall causes corrosion in
    building materials.
  • Marble and limestone (calcium carbonate) react
    with the acid structures made from them erode.

18
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.

19
Carbon Monoxide
  • Carbon monoxide binds preferentially to the iron
    in red blood cells.
  • Exposure to significant amount of CO can lower O2
    levels to the point that loss of consciousness
    and death can result.

20
Carbon Monoxide
  • Products that can produce carbon monoxide must
    contain warning labels.
  • Carbon monoxide is colorless and odorless, so
    detectors are a good idea.

21
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.

22
Photochemical Smog
  • These nitrogen oxides are just some components of
    photochemical smog.
  • Ozone, carbon monoxide, and hydrocarbons also
    contribute to air pollution that causes severe
    respiratory problems in many people.

23
Photochemical Smog
  • As a result, government emission standards for
    automobile exhaust have become continually more
    stringent.

24
Water Vapor and Carbon Dioxide
  • Gases in the atmosphere form an insulating
    blanket that causes the Earths thermal
    consistency.
  • Two of the most important such gases are carbon
    dioxide and water vapor.

25
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
    may be causing an unnatural increase in
    atmospheric temperatures.

26
Oceans
  • The vast ocean contains many important compounds
    and minerals.
  • However, the ocean is only a commercial source of
    sodium chloride, bromine, and magnesium.

27
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.

28
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.

29
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.

30
Water Purification
  • Water goes through several filtration steps.
  • CaO and Al2(SO4)3 are added to aid in the removal
    of very small particles.

31
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.

32
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 chemists should exhibit.

33
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.

34
Green Chemistry Principles
  1. Catalysts that allow the use of safe chemicals
    should be employed when possible.
  2. Try to use renewable feedstocks as raw materials.
  3. Try to reduce the amount of solvent used, and try
    to use environmentally friendly solvents.

35
Solvents
  • Solvents such as supercritical water and CO2 are
    great green alternatives.

36
Reagents
  • Phosgene, COCl2, is commonly used as a starting
    material for plastic polymers.
  • Phosgene is a highly toxic substance, and the
    by-products of many of its reactions are
    undesirable.

37
Reagents
  • A superior alternative might be dimethyl
    carbonate.
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