WHAT’S AHEAD
18.1 EARTH’S ATMOSPHERE
18.2 HUMAN ACTIVITYES AND EARTH’S ATMOSPHERE
18.3 EARTH’S WATER
18.4 HUMAN ACTIVITYES AND EARTH’S WATER
18.5 GREEN CHEMISTRY
275 K ~ 195 K
215 K ~ 275 K
290 K ~ 215 K
< 195 K
Commercial
jet aircraft
Temperature and Pressure in the Atmosphere
CHAPTER 18.1 EARTH’S ATMOSPHERE
2.3 x 10-3 torr
760 torr
75% mass of
the atmosphere
99% mass of
the atmosphere
Composition of the Atmosphere
CHAPTER 18.1 EARTH’S ATMOSPHERE
Earth’s atmosphere is
constantly bombarded by
radiation and energetic
particles from the Sun
Figure 18.2 The aurora borealis
(northern lights).
Composition of the Atmosphere
CHAPTER 18.1 EARTH’S ATMOSPHERE
Near the Earth’s surface, about 99% of the atmosphere is
composed of nitrogen and oxygen.
Composition of the Atmosphere
CHAPTER 18.1 EARTH’S ATMOSPHERE
Oxygen has a much lower bond enthalpy than nitrogen, and
is therefore more reactive.
N≡N strong, stable, 941 kJ/mol
O=O 495 kJ/mol
The outer portion of the atmosphere is the first line of
defense against radiation from the Sun.
Photodissociation & photoionization processes protect us
from high-energy radiation.
Outer regions of the atmosphere
CHAPTER 18.1 EARTH’S 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.
The rupture of a chemical bond resulting from absorption of a
photon by a molecule is called photodissociation.
Photodissociation
CHAPTER 18.1 EARTH’S ATMOSPHERE
When chemical bonds break by h, they do
so homolytically.
Homolysis: A−B → A• + B•
Oxygen in the upper atmosphere absorbs
much of this radiation before it reaches the
lower atmosphere:
at 400 km; O2 / O = 0.01
at 130 km; O2 / O = 1
below 130 km; O2 / O > 1
Photodissociation
CHAPTER 18.1 EARTH’S ATMOSPHERE
E = hν,
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? (The
dissociation energy for O2 is 495 kJ/mol.)
Solution
Shorter wavelength radiation causes electrons to
be ejected from molecules in the upper
atmosphere; very little of this radiation reaches the
Earth’s surface.
Photoionization
CHAPTER 18.1 EARTH’S ATMOSPHERE
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.
About 90% of Earth’s ozone is found in the stratosphere.
M = N2 or O2.
Ozone
CHAPTER 18.1 EARTH’S ATMOSPHERE
Ozone
CHAPTER 18.1 EARTH’S ATMOSPHERE
Figure 18.4
Variation in ozone
concentration in the
atmosphere as a function
of altitude.
CHAPTER 18.2 HUMAN ACTIVITIES AND EARTH’S ATMOSPHERE
Figure 18.5
Mount Pinatubo erupts,
June 1991.
• 10% drop in the
amount of sunlight
• 0.5 °C drop in Earth’s
surface temperature
CHAPTER 18.2 HUMAN ACTIVITIES AND EARTH’S ATMOSPHERE
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.
Ozone Depletion
CHAPTER 18.2 HUMAN ACTIVITIES AND EARTH’S ATMOSPHERE
The chlorine atoms formed react with
ozone:
CFCs (CFCl3, CF2Cl2) 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)
The C—Cl bond is easily broken, though, when the
molecule absorbs radiation with a wavelength between 190
and 225 nm.
Chlorofluorocarbon
CHAPTER 18.2 HUMAN ACTIVITIES AND EARTH’S ATMOSPHERE
Sulfur dioxide (SO2) is a by-product of the burning
of coal or oil.
It reacts with moisture in the air to form sulfuric
acid.
SO2 → SO3
SO3 + H2O → H2SO4
[O]
Sulfur compounds and acid rain
CHAPTER 18.2 HUMAN ACTIVITIES AND EARTH’S ATMOSPHERE
It is primarily responsible
for acid rain.
Although its concentration
is low, SO2 is regarded as
the most serious health
hazard
Sulfur compounds and acid rain
CHAPTER 18.2 HUMAN ACTIVITIES AND EARTH’S ATMOSPHERE
Figure 18.7 Water pH values from freshwater sites across
the United States, 2008.
High acidity in rainfall causes corrosion in
building materials.
Marble and limestone (calcium carbonate) react
with the acid; structures made from them erode.
Sulfur compounds and acid rain
CHAPTER 18.2 HUMAN ACTIVITIES AND EARTH’S ATMOSPHERE
Figure 18.8 Damage
from acid rain.
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.
Sulfur compounds and acid rain
CHAPTER 18.2 HUMAN ACTIVITIES AND EARTH’S ATMOSPHERE
Figure 18.9 One method for removing SO2 from combusted fuel.
Carbon monoxide binds
preferentially to the iron
in red blood cells.
CO binds to hemoglobin
over 200 times stronger
than O2 does.
Formed by the incomplete combustion of carbon-
containing material such as fossil fuels.
Carbon monoxide
CHAPTER 18.2 HUMAN ACTIVITIES AND EARTH’S ATMOSPHERE
Exposure to significant amount of CO can lower
O2 levels to the point that loss of consciousness
and death can result.
Only 0.1% CO can convert more than half of Hb
into COHb
Products that can produce carbon monoxide
must contain warning labels.
Carbon monoxide is colorless and odorless.
Carbon monoxide
CHAPTER 18.2 HUMAN ACTIVITIES AND EARTH’S ATMOSPHERE
Nitrogen oxides are primary
components of smog.
The majority of nitrogen oxide
emissions comes from cars,
buses, and other forms of
transportation.
Nitrogen oxides
CHAPTER 18.2 HUMAN ACTIVITIES AND EARTH’S ATMOSPHERE
Figure 18.10 Photochemical smog is produced largely by the action of
sunlight on vehicle exhaust gases.
Ozone, carbon monoxide,
and hydrocarbons also
contribute to air pollution
that causes severe
respiratory problems in
many people.
A photochemical smog is the chemical reaction of sunlight,
nitrogen oxides (NOx) and volatile organic compounds (VOCs)
in the atmosphere, which leaves airborne particles (called
particulate matter) and ground-level ozone. (Wikipedia)
Photochemical smog
CHAPTER 18.2 HUMAN ACTIVITIES AND EARTH’S ATMOSPHERE
The average surface temperature of the Earth would
be 254 K, without gases in the atmosphere.
The 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
CHAPTER 18.2 HUMAN ACTIVITIES AND EARTH’S ATMOSPHERE
But increasing levels of CO2 in the atmosphere may
be causing an unnatural
increase in atmospheric
temperatures.
A liter of gasoline
produces about
2 kg of CO2.
This blanketing effect is known as the “greenhouse effect.”
Water vapor, with its high specific heat, is a major factor in this moderating effect.
Water vapor and carbon dioxide
CHAPTER 18.2 HUMAN ACTIVITIES AND EARTH’S ATMOSPHERE
72% of Earth’s surface is covered in water
Our bodies are about 65% water by mass
Water’s highly polar character
Many reactions occur in water
Water itself is a reactant
A proton donor/acceptor
The world ocean
CHAPTER 18.3 EARTH’S WATER
Oceans contain 97.2% of the Earth’s water
• Ice caps/glaciers (2.1%), freshwater (0.6%), salty
water (0.1%)
Seawater
CHAPTER 18.3 EARTH’S WATER
Contains
about 3.5%
dissolved
salts by mass.
The salinity of seawater
is the mass in grams of
dry salts present in 1 kg
of sea water.
CO2 absorption and buffering (pH 8.0~8.3)
Properties of Seawater
CHAPTER 18.3 EARTH’S WATER
Figure 18.16 Average temperature, salinity, and density of seawater as
a function of depth.
Dissolved oxygen amount can indicate
water quality
• At 1 atm, 20 °C, water fully saturated with air has
9 ppm oxygen
• Cold-water fish require at least 5 ppm oxygen.
Organic materials that bacteria can oxidize
reduce oxygen content.
Plant nutrients contribute to water pollution
by stimulating excessive growth of aquatic
plants (floating algae)
Water Quality
CHAPTER 18.4 HUMAN ACTIVITIES AND EARTH’S WATER
floating algae
Water Quality
CHAPTER 18.4 HUMAN ACTIVITIES AND EARTH’S WATER
Figure 18.18 Eutrophication. This rapid accumulation of dead and
decaying plant matter in a body of water uses up the water’s oxygen
supply, making the water unsuitable for aquatic animals
“Water, water everywhere,
and not a drop to drink.”
• Seawater has too high a
concentration of NaCl for
human consumption.
For drinkable water, NaCl
content should be less than
about 0.05%.
Seawater can be desalinated
through distillation or reverse
osmosis.
Desalination
CHAPTER 18.4 HUMAN ACTIVITIES AND EARTH’S WATER
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.
Reverse osmosis
CHAPTER 18.4 HUMAN ACTIVITIES AND EARTH’S WATER
Clean, safe fresh water
supplies are of the
utmost importance to
society.
Ocean water
evaporates, water
vapor accumulates in
the atmosphere
• Returns as rain or
snow
Desalination plants, Saudi Arabia
Fresh water
CHAPTER 18.4 HUMAN ACTIVITIES AND EARTH’S WATER
Water goes through several filtration steps.
CaO and Al2(SO4)3 are added to aid in the removal
of very small particles.
Water Purification
CHAPTER 18.4 HUMAN ACTIVITIES AND EARTH’S WATER
Figure 18.20 Common steps in treating water for a public water system.
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.
Water Purification
CHAPTER 18.4 HUMAN ACTIVITIES AND EARTH’S WATER
Water Purification
CHAPTER 18.4 HUMAN ACTIVITIES AND EARTH’S WATER
Figure 18.21 A LifeStraw
purifies water as it is drunk.
Hard water contains a relatively high concentration of Ca2+, Mg2+, and other divalent cations (soap scum formation….)
Water Softening
CHAPTER 18.4 HUMAN ACTIVITIES AND EARTH’S WATER
Water softening by ion exchange
Figure 18.22 Scale formation.
heat (pH drops)
Municipal water-softening operations
Our planet is a closed system.
All the processes we carry out should be in
balance with Earth’s natural processes and
physical resources.
It is necessary to design and apply
chemical products and processes that are
compatible with human health and that
preserve the environment.
Green Chemistry
CHAPTER 18.5 GREEN CHEMISTRY
1. Rather than worry about waste
disposal, it is better to avoid creating
waste in the first place.
2. In addition to generating as little waste
as possible, try to make waste that is
nontoxic.
3. Be energy-conscious in designing
syntheses.
Green Chemistry Principles
CHAPTER 18.5 GREEN CHEMISTRY
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.
CHAPTER 18.5 GREEN CHEMISTRY
Green Chemistry Principles
Toxic and expensive starting materials, high temp, multisteps
Less toxic and expensive starting materials, low temp, single step
Green Chemistry
CHAPTER 18.5 GREEN CHEMISTRY