CHAPTER 3: THE CHEMISTRY OF GLOBAL WARMING
CHAPTER 3: THE CHEMISTRY OF GLOBAL WARMING
Emphasizing Essentials
1.
a. Yes. Earth is warmer than predicted based on distance from the Sun and the amount of radiation reaching
the earth. Without the greenhouse effect, our planet would be too cold to be hospitable to life as we know
it.
b. Yes. Most scientists now conclude that observed increases in Earth’s average temperature are evidence
that enhanced greenhouse effect, or global warming, is taking place.
2.
A good deal of this CO2 dissolves in the oceans, where it can react with calcium in seawater to form
calcium carbonate, CaCO3. This environmental “sink” still exists for CO2, but the rate of the reaction is
very slow. Another removal mechanism was the development of plants that were capable of
photosynthesis.
3.
The “windows” of the greenhouse are made of molecules that are transparent to visible light, but absorb in
the infrared region of the spectrum.
4.
6 CO2(g) + 6 H2O(l) C6H12O6(aq) + 6 O2(g)
a. The number of atoms of each element on either side is the same. C = 6, O = 18, H = 12
b. The number of molecules is not the same on either side of the equation. There are 12 on the left, but
only 7 on the right. The large molecule glucose has formed on the product side of the equation, using 24
atoms per molecule.
5.
Weather describes whatever is happening outdoors in a given place at a given time. Climate describes the
total of all weather occurring over a period of years in a given place.
6.
a. 343 W ! 30 parts = 103 W
2
2
1m
100 parts
m
b. Under steady state conditions, 103 W/m2 leaves our atmosphere.
7.
a. The atmospheric CO2 concentration at the present time is about 376 ppm while 20,000 years ago, the
concentration was only about 190 ppm. However, 120,000 years ago this concentration was about 370 ppm,
close to today’s levels.
b. The mean atmospheric temperature at present is somewhat above the 1950-1980 mean atmospheric
temperature. 20,000 years ago, the mean atmospheric temperature was lower by about 9 °C. However,
120,000 years ago the mean atmospheric temperature was lower by only about 1 °C than it is at present.
c. While there appears to be a correlation between mean atmospheric temperature and CO2 concentration,
this Figure does not prove causation of either factor by the other.
8.
Even though the amount of energy emitted is more than double the amount received, the Earth does not
cool rapidly because the atmosphere retains much of the emitted heat energy.
9.
a. Visible light can enter through the glass, but infrared radiation cannot leave through the glass. There also
is no circulation of air, so the heat cannot be dissipated and the temperature inside the car increases.
b. On clear nights the heat from the Earth can be more completely radiated into space, whereas water vapor
in the clouds absorbs the heat, retaining it. In the atmosphere, water vapor is one of the greenhouse gases.
c. In the desert, there is very little water vapor to help trap infrared radiation. In the atmosphere, water
vapor is one of the greenhouse gases.
SECTION F PAGE 18
ANSWERS TO END-OF-CHAPTER QUESTIONS
CHAPTER 3: THE CHEMISTRY OF GLOBAL WARMING
10. These are the two Lewis structures.
H—H and
For H2 with only two atoms, the atoms can only be arranged in a straight line. For H2O, even though the
Lewis structure has been shown as a straight line, this does not mean that the molecule is linear. In fact,
the bent structure of water is so well known that the Lewis structure is often written in this manner.
11. The actual distances measured will depend on the model kit used. In every case, however, the distance
between the hydrogen atoms in a square arrangement will be less than the distance between the
hydrogen atoms in the tetrahedral arrangement. This is because the angle separating the hydrogen
atoms is greater in the tetrahedral arrangement.
Cl
12. a. 4 + 2(1) + 2(7) = 20 outer electrons; The Lewis structure is H C H and the shape is tetrahedral.
Cl
b. 4 + 6 = 10 outer electrons. The Lewis structure is
C O
and the shape is linear. This shape could
have been predicted from the fact that there are just two atoms per molecule.
c. 1 + 4 + 5 = 10 outer electrons. The Lewis structure is H C N
The shape is linear.
d. 5 + 3(1) = 8 outer electrons. The Lewis structure is H P H The shape is triangular pyramidal
H
which can also be called trigonal pyramidal.
H
H
C O H
13. a. 3(1) + 4 + 6 + 1 = 14 outer electrons. This is the Lewis structure.
H
b. The geometry around the carbon atom is tetrahedral and there are no lone pairs. A
hydrogen-to-carbon-to-hydrogen bond angle of 109.5 ° is predicted.
c. There are four pairs of electrons around the oxygen atom, two of which are bonding pairs and two
are nonbonded pairs. Repulsion between the two nonbonded electron pairs and their repulsion of the
bonding pairs is predicted to cause the hydrogen-to-oxygen-to-carbon bond angle to be slightly less
than
109.5 °.
14. a. 2(1) + 4 + 4 + 2(1) = 12 outer electrons. This is the Lewis structure. H C C H
H H
b. Note that there are three regions of bonded electrons around each carbon. To achieve maximum
separation of the three regions, which will mutually repel on another, a
hydrogen-to-carbon-to-hydrogen
bond angle of 120 ° is predicted.
H
H
C C
c. This is the structure with the predicted bond angle indicated.
H
15. a. E =
120 °
H
hc
can be used to calculate the energies.
!
For the 320 nm UV photon: E =
6.63 " 10 !34 J # s "3.00 " 10 8 m / s
= 6.21 " 10 !19 J
1m
320 nm " 9
10 nm
ANSWERS TO END-OF-CHAPTER QUESTIONS
SECTION F PAGE 19
CHAPTER 3: THE CHEMISTRY OF GLOBAL WARMING
For the 5000 nm IR photon: E =
6.63 " 10 !34 J # s "3.00 " 108 m / s
= 3.98 " 10 !20 J
1m
5000 nm " 9
10 nm
b. The ratio of the energy that breaks bonds to the energy that causes vibration is:
6.21 ! 10 "19 J
= 15.6 or approximately 16 times higher. This helps to explain why UV photons are capable
3.98 ! 10 -20 J
of breaking bonds, but IR photons only cause vibrations.
16. All of them can contribute to the greenhouse effect. In every case, as the bond stretches the atoms move
and therefore the charge distribution changes. Unlike linear CO2, water molecules are bent and so the
polarity of the molecule changes with each of these modes of vibration.
17. a. E =
hc
can be used to calculate the energies.
!
6.63 " 10 !34 J # s "3.00 " 108 m / s
E=
= 4.67 " 10 !20 J
1m
4.26 µm " 6
10 µm
E=
6.63 " 10 !34 J # s "3.00 " 108 m / s
= 1.3 " 10 !22 J
1m
1500 µm " 6
10 µm
b. If the vibrating molecule CO2 meets another CO2 molecule, the energy can be transferred to that
molecule. The energy can also be spontaneously emitted back to the atmosphere or into space.
18. The water cycle that occurs in our atmosphere is a naturally occurring phenomenon. There is no need or
method for regulating its concentration as it does not accumulate.
19. a. Volcanic eruptions place large amounts of ash into the atmosphere. Often this ash diffuses into the
atmosphere and remains there for a considerable amount of time. The ash will reflect incoming sunlight and
have a cooling effect.
b. CFCs in the troposphere can also act as greenhouse gases. CFCl3, for example, has the same geometry as
methane, CH4. CFCs in the troposphere have a warming effect.
c. CFCs in the stratosphere react with ozone, O3, and reduce the concentration of ozone in the stratosphere.
Because ozone is also a greenhouse gas, CFCs in the stratosphere have a cooling effect. However,
reduction of the stratospheric ozone concentration allows more UV-A radiation to reach the Earth’s surface,
which causes warming.
20. C6H12O6(aq)
yeast
2 C2H5OH(aq) + 2 CO2(g)
21. a. The major source is from utilities, followed by transportation, and then industrial uses.
b. For utilities, alternatives include nuclear power and solar energy. For transportation, alternatives include
use of community transportation such as rapid transit, light rail, or bus lines. Another alternative is to
change to alternate energy sources, such as are discussed in Chapter 8. For industrial uses, natural gas may
be used to replace other fossil fuels, with savings in CO2 emissions.
22. a. 47 protons, 60 neutrons, 47 electrons
b. 47 protons, 62 neutrons, 47 electrons. Only the number of neutrons has changed.
SECTION F PAGE 20
ANSWERS TO END-OF-CHAPTER QUESTIONS
CHAPTER 3: THE CHEMISTRY OF GLOBAL WARMING
23. The weighted average for silver can be found on the periodic table. It is 107.870 g/mole. There are just
two isotopes. Silver-107 accounts for 52% of natural silver. Let x be the mass number of the other
isotope, which must account for (100% – 52%) or 48% of the mass.
Then: (107 × 0.52) + (x × 0.48) = 107.870
Solving for x: 0.48 x = 107.870 – 55.64
x = 109; The other isotope of silver is silver-109.
It is interesting to note that silver-108 is not a stable isotope.
24. a.
107.870g
1mole
1.79 " 10 !22 g
"
=
1 mole
atom
6.02 " 10 23 atoms
1.79 ! 10 "22 g
! 10 ! 1012 atoms = 1.79 ! 10 -9 g
atom
1.79 ! 10 -22 g
c. 5.00 ! 10 45 atoms !
= 8.95 ! 10 23 g
atoms
b.
25. a. 2(1.0) + 16.0 = 18.0 g/mole
b. 12.0 + 2(19.0) + 2(35.5) = 121.0 g/mole
c. 14.0 + 16.0 = 30.0 g/mole
26. a. Mass percent Cl in CCl3F (Freon-11) is:
3(35.5)
! 100 = 77.5%
12.0 + 3(35.5)+ 19.0
b. Mass percent Cl in CCl2F2 is 58.7%
c.. Freon-11: 77.5 g; Freon-12: 58.7g
d. Freon-11: 6.6 x1023 Cl2 molecules; Freon-12: 5.0 x 1023 Cl2 molecules
27. Concentration of carbon atoms =
7.5 ! 1017 g
7.5 ! 10 22 g
! 100 = 0.001% ;
0.001parts C
x partsC
=
; x = 10 ppm
100parts C in earth 1,000,000partsCin earth
28. a. There has been a 32% increase in CO2 concentration between preindustrial time and 2002.
b.
1.8 ppm " 0.70 ppm
! 100 = 160% increase in the concentration of CH4
0.70 ppm
0.31ppm " 0.28ppm
! 100 = 11%increase in the concentration of N2O
0.28ppm
The largest percentage increase has been shown by CH4.
29. a. CO2
b. Although CO2 accounts for the largest percentage of greenhouse gas contributions, the case could be
made that N2O has the greatest impact. It is almost 300 times more effective than CO2, but its
concentration is far lower than that of either CO2 or CH4.
ANSWERS TO END-OF-CHAPTER QUESTIONS
SECTION F PAGE 21
CHAPTER 3: THE CHEMISTRY OF GLOBAL WARMING
Gas
CO2
CH4
N2O
% contribution
(graph)
55
15
5
GWP
(Table 3.5)
1
23
296
Net Effectiveness
(product)
0.6
3.5
14.8
Although CO2 accounts for the largest percentage of greenhouse gas
emissions, the net effectiveness of N2O is the largest of these three
gases.
30. Yes. 1.8 ppm is equivalent to 1.8 x 10-4 %.
Concentrating on Concepts
31. a. This is an example of causation. If more coal is burned, more CO2 will be emitted.
b. This is an example of correlation. In more highly developed countries with higher per capita income,
more fossil fuels are burned for energy, causing higher per capita emissions of CO2.
c. This is considered by most people to be an example of causation. The evidence is quite extensive that
links the incidence of lung cancer to smoking.
d. This is an example of causation. The length of an oxygen-to-oxygen single bond is greater than the
length of an oxygen-to-oxygen double bond.
e. This might be correlation, but simply having a greenhouse does not necessarily mean that beautiful
tropical plants will be raised. It may be necessary to put in a heater, and to have the time and expertise to
cause beautiful tropical plants to grow.
f. This might be correlation, but many people buy roller blades and do not have an accident. There are
many other ways to break a leg.
32. Living plants are still carrying out the process of photosynthesis, which removes CO2 from the atmosphere
and increases the concentration of beneficial O2. Another reason is that the plants will have a far longer
lifetime than cut flowers, an economic benefit for you and a longer lasting reminder of your kindness for
your friend.
33. Drilled ocean cores can be analyzed for the number of type of microorganisms present. Another correlating
piece of evidence is the changing alignment of magnetic field in particles in the sediment over time.
Another possibility is to analyze the deuterium-to-hydrogen ratio in ice cores.
34. Atmospheric concentrations of CO2 at Mauna Loa are dependent on seasonal variation and so are
extremely regular. The emissions of CO2 decrease during the summer when plant growth fixes CO2
through photosynthesis. The temperature changes in Figure 3.5 depend on many factors, including natural
long-range cycles that are not fully understood. Mankind’s influence on these values since the industrial
revolution may be changing the delicate temperature balance of the Earth.
35. a. Transportation, utilities, commercial, and industrial have increased. Residential has decreased.
b. Individuals can consider cutting back on the use of electricity in the home, restricting use of cars and
trucks as effective measures, particularly if a significant number of people made those changes.
c. The entire quantity of CO2 emitted does not end up in the atmosphere. Some CO2 will be dissolved in
rain, snow, and fog. Eventually this dissolved CO2 will find its way into ground water and into the ocean.
Some CO2 will be used in photosynthesis and in other biochemical processes.
SECTION F PAGE 22
ANSWERS TO END-OF-CHAPTER QUESTIONS
CHAPTER 3: THE CHEMISTRY OF GLOBAL WARMING
36. Lewis dot structures are very good at showing which atom is joined with another, but the representation on
paper does not necessarily indicate the molecular geometry. That must be predicted by looking at the
number
of bonded electron pairs and lone electron pairs around the central atom. Using H2O as an example, it
has 2(1) + 6 = 8 electrons. This is the Lewis structure.
H
O
H
The Lewis structure was drawn to show that a hydrogen atom is linked to an oxygen atom, which is
linked to another hydrogen atom. There are two lone electron pairs. Far from being linear, which might
have been incorrectly predicted looking at this two-dimensional Lewis structure, the H2O molecule is
bent with a bond angle somewhat less than 109.5° because of electron pair repulsion.
37. Substances that absorb visible light have observable color. For example, if the wavelengths associated
with red light are absorbed, the object appears green. Because we cannot see any color associated with
either carbon dioxide gas or water vapor, it is likely that they do not absorb visible light.
38. The energy required would be smaller for each of the IR-absorbing vibrations if single bonds were
present. In general, single bonds between atoms are somewhat weaker than double bonds, and
therefore less energy will be required to cause vibrations. A carbon-to-oxygen single bond can be
broken with 336 kJ of energy per mole, but it requires 803 kJ of energy per mole of carbon-to-oxygen
double bonds in CO2.
39. Water in the food substances will absorb microwave radiation because of the polar
hydrogen-to-oxygen-to hydrogen bonds. The non-polar hydrogen-to-carbon-to-hydrogen bonds in the
plastic container do not respond to microwave radiation.
40. a. C2H5OH + 3 O2 → 3 H2O + 2 CO2
b. 2 mol CO2
c. 30 mol O2
41. a. C6H14 + 9.5 O2 → 7 H2O + 6 CO2
b. C8H18 + 12.5 O2 → 9 H2O + 8 CO2
c. One mole of hexane produces 6 mol CO2, and one mol of octane produces 8 mol of CO2.
42. The atmospheric lifetime is important because it helps to determine if a potential greenhouse gas is
really important. If there are efficient environmental removal mechanisms for a greenhouse gas (that is
if it has a short atmospheric lifetime) the gas will accumulate in the atmosphere more slowly than
predicted by the rate at which it is emitted. If a greenhouse has had a long atmospheric lifetime, then
even though not a lot of it is emitted from various sources, the atmospheric concentration of the gas
will continually increase, allowing the gas to contribute more to global warming than would be
expected.
43. The molecules of CO2 and N2 are constantly in motion in the atmosphere. They are also spread very far
apart, and are homogeneously mixed. Unlike liquids with different densities that will settle into layers
if they are not soluble in each other, atmospheric gases mix with each other completely.
44. Water in the atmosphere can absorb the microwave radiation, interfering with the detection of the
intended objects.
ANSWERS TO END-OF-CHAPTER QUESTIONS
SECTION F PAGE 23
CHAPTER 3: THE CHEMISTRY OF GLOBAL WARMING
45. 73 ! 10 6 metric tons CH 4 !
12 metric tons C
= 5.5 ! 10 7 metric tons C
16 metric tons CH 4
46. This observation does not prove that global warming theories are correct. It is a short-range
observation that is consistent with global warming trends that are predicted, but it may not predict
large-scale or long-range changes.
47. a. From this information, HFC-152a appears to be the best choice. It has a lower GWP and a shorter
lifetime.
b. Other considerations include cost, toxicity, flammability, boiling point, and stability.
48. a. The species might be migrating north due to increasing annual temperatures.
b. The species might be moving out of southern California due to increased development and human
activity.
c. Proposed plans will vary, they may include restricting development and tighter controls on greenhouse
gases.
49. a. The United States, Australia, Norway, and Tasmania.
b. Every metric ton of CO2 contains 0.27 metric tons of carbon.
c. The two tables are in relative agreement: The figure in this question indicates that the U.S. releases over
15 metric tons per person. Taking in to consideration the mass percent of carbon in carbon dioxide, this
represents a minimum of 4 metric tons of carbon per person. Figure 3.27 shows the U.S. per capita metric
tons of carbon at about 5.3
50. a. Kilograms of oil equivalent.
b. Kuwait, the United States, and Canada.
c. Gross Domestic Product (GNP)
d. Brazil
e. When comparing the U.S. with most of the countries on this graph, we see that the U.S. falls short in
creating wealth from its use of energy.
Exploring Extensions
51. In BF3, there are 3 + 3(7) = 24 outer electrons. This is the Lewis structure.
F B F
F
In NF3, there are 5 + 3(7) = 26 outer electrons. This is the Lewis structure.
F
N
F
F
Note that in BF3, there are just three pairs of electrons around the central boron. To achieve maximum
separation of these three electron regions, which will mutually repel, a fluorine-to-boron-to-fluorine bond
angle of 120 ° is predicted. This is why BF3 has a triangular planar geometry. In NF3, however, there are
four pairs of electrons - three bonded pairs and one lone pair. This determines the triangular pyramidal
geometry. Although the predicted fluorine-to-nitrogen-to-fluorine bond angle is 109.5°, the repulsion of the
lone pair with the bonded pairs closes the angle somewhat. The experimentally measured angle is 107.5°.
SECTION F PAGE 24
ANSWERS TO END-OF-CHAPTER QUESTIONS
CHAPTER 3: THE CHEMISTRY OF GLOBAL WARMING
52. a. 20 electrons are required if 3 atoms join. This is the general Lewis structure.
X Y Z
b. This molecule will be bent. There are four pairs of electrons around the central Y atom. Two of the pairs
are bonding pairs, and there are two lone pairs. Repulsion between the two lone pairs and their repulsion of
the bonding pairs is predicted to cause the bond angle to be less than 109.5 oC.
c. There are new possibilities if double and triple bonds are allowed.
Number of Outer electrons Lewis Structure
Shape
Predicted bond angle
53.
18
X Y Z
bent
less than 120°
16
X Y Z
linear
180°
16
X Y Z
linear
180°
The data are from NASA Goddard Institute for Space Studies. A visit to their website will be
helpful in starting to address this question; http://www.giss.nasa.gov/research/observe/surftemp/
54. a. There are two absorption peaks for H2O in the IR spectrum. According to Figure 3.15, one occurs at
hc
a wavelength of 6.27 µm and the other at a wavelength of 2.66 µm. E =
can be used to calculate
!
the energies.
6.63 " 10 !34 J # s "3.00 " 10 8 m / s
E=
= 3.17 " 10 ! 20 J
1m
6.27 µm " 6
10 µm
E=
6.63 " 10 !34 J # s "3.00 " 10 8 m / s
= 7.48 " 10 ! 20 J
1m
2.66 µm " 6
10 µm
b. The absorption peak with the lower wavelength, 2.66 µm, is the one with the higher energy.
c. Bending.
55. This is the general equation for complete combustion of a hydrocarbon. The coefficients must be
supplied to balance a combustion equation for a specific hydrocarbon.
__CxHy + __O2 → __CO2 + __H2O
Combustion is a major way that human activities impact levels of CO2 in the atmosphere. If
ever-increasing volumes of CO2 are released, the substance accumulates because the removal
mechanisms are very slow. Although water vapor is also released in combustion processes, water does
not accumulate in the atmosphere because the removal mechanisms such as rain and snow are too
efficient. These are the reasons that the differences in the two trends do not disprove the connection
between man’s activities and global warming.
56. a. 1196 mol.
b. 52.6 kg
c. 0.058 ton
d. 116 lb
ANSWERS TO END-OF-CHAPTER QUESTIONS
SECTION F PAGE 25
CHAPTER 3: THE CHEMISTRY OF GLOBAL WARMING
57. a. The difference in the data sets is the more accurate prediction of the atmospheric lifetime of CO2 and
N2O gases. This is due to the fact that there is now better scientific data regarding the removal of these
gases from the atmosphere.
b. The rate of concentration increase is greatest for CO2 due to the large amounts of fossil fuel burning.
Having a more precise idea of the atmospheric lifetime of CO2 will be helpful when crafting legislation
to control emissions.
58. a. As the per capita income rises, the CO2 emissions rise. Economic growth usually means increased use of
fossil fuels, which leads to increased CO2 emissions.
b. Part of the Kyoto agreement guarantees that developed countries will help developing countries to use
technology that will help them meet their target CO2 emissions without slowing growth. There is an
elaborate system of trade-off credits that will help facilitate this process.
59.
The following site provides data from Bailis’ work: http://ist-socrates.berkeley.edu/~rael/OA5.1.pdf
60. a. There are several reasons that can be suggested. The evidence for ozone depletion was more convincing
than the accumulated evidence for global warming, which has many skeptics questioning whether or not we
know enough to understand the trend. The effects of ozone depletion are well defined, but the effects of
global warming are to a larger extent, more uncertain. Ozone depletion is primarily caused by a limited
group of man-made chemicals, the CFCs. Global warming is primarily caused by CO2, which is a natural
component of the atmosphere that is being influenced by man’s activities. Controlling ozone depletion has
economic impacts, the production of greenhouse gases, particularly CO2, is very closely tied to the
economic development of a country. This produces a much greater impact on a society, and sets up tensions
between developed and developing countries.
b. Montreal Protocol: last amendment was Beijing in February, 2001. The total number of Parties that
have ratified the Montreal Protocol as of the printing of the 5 th edition was 186. Decreases in stratospheric
chlorine have begun. As of as of April 15, 2004, 122 countries had ratified or acceded to the Kyoto
Protocol. But those countries represent only 44.2% of the total CO2 emissions from industrialized countries
in 1990. The United States - the world's largest emitter - withdrew from Kyoto in 2001, so the only way
that the Protocol will enter into force now is if Russia ratifies the agreement. Levels of greenhouse gases
have not declined as a result of the Kyoto Protocol.
SECTION F PAGE 26
ANSWERS TO END-OF-CHAPTER QUESTIONS