THE BIG ISLAND of Hawaii

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

Composition of the Atmosphere

CHAPTER 18.1 EARTH’S ATMOSPHERE

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

The global water cycle

CHAPTER 18.3 EARTH’S WATER

Figure 18.15 The global water cycle.

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

Atom economy process

CHAPTER 18.5 GREEN CHEMISTRY

A common intermediate

used to make polymers

Atom economy process

CHAPTER 18.5 GREEN CHEMISTRY

“Click Reaction”