THE BIG ISLAND of Hawaii

Transcription

1 THE BIG ISLAND of Hawaii

2 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

3 CHAPTER 18.1 EARTH S ATMOSPHERE Temperature and Pressure in the Atmosphere < 195 K 2.3 x 10-3 torr 275 K ~ 195 K 99% mass of the atmosphere Commercial jet aircraft 215 K ~ 275 K 290 K ~ 215 K 75% mass of the atmosphere 760 torr

4 CHAPTER 18.1 EARTH S ATMOSPHERE Composition of the Atmosphere Earth s atmosphere is constantly bombarded by radiation and energetic particles from the Sun Figure 18.2 The aurora borealis (northern lights).

5 CHAPTER 18.1 EARTH S ATMOSPHERE Composition of the Atmosphere Near the Earth s surface, about 99% of the atmosphere is composed of nitrogen and oxygen.

6 CHAPTER 18.1 EARTH S ATMOSPHERE Composition of the 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

7 CHAPTER 18.1 EARTH S ATMOSPHERE Composition of the Atmosphere

8 CHAPTER 18.1 EARTH S ATMOSPHERE Outer regions of the 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.

9 Photodissociation 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.

10 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; O 2 / O = 0.01 at 130 km; O 2 / O = 1 below 130 km; O 2 / O > 1

11 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 O 2 molecule? (The dissociation energy for O 2 is 495 kj/mol.) Solution E = hν,

12 Photoionization CHAPTER 18.1 EARTH S ATMOSPHERE Shorter wavelength radiation causes electrons to be ejected from molecules in the upper atmosphere; very little of this radiation reaches the Earth s surface.

13 Ozone 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 = N 2 or O 2.

14 Ozone CHAPTER 18.1 EARTH S ATMOSPHERE Figure 18.4 Variation in ozone concentration in the atmosphere as a function of altitude.

15 CHAPTER 18.2 HUMAN ACTIVITIES AND EARTH S ATMOSPHERE Figure 18.5 Mount Pinatubo erupts, June % drop in the amount of sunlight 0.5 C drop in Earth s surface temperature

16 CHAPTER 18.2 HUMAN ACTIVITIES AND EARTH S ATMOSPHERE

17 CHAPTER 18.2 HUMAN ACTIVITIES AND EARTH S ATMOSPHERE 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.

18 CHAPTER 18.2 HUMAN ACTIVITIES AND EARTH S ATMOSPHERE Chlorofluorocarbon CFCs (CFCl 3, CF 2 Cl 2 ) 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. The chlorine atoms formed react with ozone:

19 CHAPTER 18.2 HUMAN ACTIVITIES AND EARTH S ATMOSPHERE Sulfur compounds and acid rain Sulfur dioxide (SO 2 ) 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. Although its concentration is low, SO 2 is regarded as the most serious health hazard [O] SO 2 SO 3 SO 3 + H 2 O H 2 SO 4

20 CHAPTER 18.2 HUMAN ACTIVITIES AND EARTH S ATMOSPHERE Sulfur compounds and acid rain Figure 18.7 Water ph values from freshwater sites across the United States, 2008.

21 CHAPTER 18.2 HUMAN ACTIVITIES AND EARTH S ATMOSPHERE Sulfur compounds and acid rain High acidity in rainfall causes corrosion in building materials. Marble and limestone (calcium carbonate) react with the acid; structures made from them erode. Figure 18.8 Damage from acid rain.

22 CHAPTER 18.2 HUMAN ACTIVITIES AND EARTH S ATMOSPHERE Sulfur compounds and acid rain SO 2 can be removed by injecting powdered limestone which is converted to calcium oxide. The CaO reacts with SO 2 to form a precipitate of calcium sulfite. Figure 18.9 One method for removing SO 2 from combusted fuel.

23 CHAPTER 18.2 HUMAN ACTIVITIES AND EARTH S ATMOSPHERE Carbon monoxide Formed by the incomplete combustion of carboncontaining material such as fossil fuels. Carbon monoxide binds preferentially to the iron in red blood cells. CO binds to hemoglobin over 200 times stronger than O 2 does.

24 CHAPTER 18.2 HUMAN ACTIVITIES AND EARTH S ATMOSPHERE Carbon monoxide Exposure to significant amount of CO can lower O 2 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.

25 CHAPTER 18.2 HUMAN ACTIVITIES AND EARTH S ATMOSPHERE Nitrogen oxides Nitrogen oxides are primary components of smog. The majority of nitrogen oxide emissions comes from cars, buses, and other forms of transportation. Figure Photochemical smog is produced largely by the action of sunlight on vehicle exhaust gases.

26 CHAPTER 18.2 HUMAN ACTIVITIES AND EARTH S ATMOSPHERE Photochemical smog A photochemical smog is the chemical reaction of sunlight, nitrogen oxides (NO x ) and volatile organic compounds (VOCs) in the atmosphere, which leaves airborne particles (called particulate matter) and ground-level ozone. (Wikipedia) Ozone, carbon monoxide, and hydrocarbons also contribute to air pollution that causes severe respiratory problems in many people.

27 CHAPTER 18.2 HUMAN ACTIVITIES AND EARTH S ATMOSPHERE Water vapor and carbon dioxide 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.

28 CHAPTER 18.2 HUMAN ACTIVITIES AND EARTH S ATMOSPHERE 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 CO 2 in the atmosphere may be causing an unnatural increase in atmospheric temperatures. A liter of gasoline produces about 2 kg of CO 2.

29 The world ocean CHAPTER 18.3 EARTH S WATER 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

30 The global water cycle CHAPTER 18.3 EARTH S WATER Figure The global water cycle.

31 Seawater 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%) 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.

32 Properties of Seawater CHAPTER 18.3 EARTH S WATER CO 2 absorption and buffering (ph 8.0~8.3) Figure Average temperature, salinity, and density of seawater as a function of depth.

33 CHAPTER 18.4 HUMAN ACTIVITIES AND EARTH S WATER Water Quality 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)

34 CHAPTER 18.4 HUMAN ACTIVITIES AND EARTH S WATER Water Quality floating algae Figure 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

35 CHAPTER 18.4 HUMAN ACTIVITIES AND EARTH S WATER Desalination 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.

36 CHAPTER 18.4 HUMAN ACTIVITIES AND EARTH S WATER 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.

37 CHAPTER 18.4 HUMAN ACTIVITIES AND EARTH S WATER Fresh 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

38 CHAPTER 18.4 HUMAN ACTIVITIES AND EARTH S WATER Water Purification Water goes through several filtration steps. CaO and Al 2 (SO 4 ) 3 are added to aid in the removal of very small particles. Figure Common steps in treating water for a public water system.

39 CHAPTER 18.4 HUMAN ACTIVITIES AND EARTH S WATER 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.

40 CHAPTER 18.4 HUMAN ACTIVITIES AND EARTH S WATER Water Purification Figure A LifeStraw purifies water as it is drunk.

41 CHAPTER 18.4 HUMAN ACTIVITIES AND EARTH S WATER Water Softening Hard water contains a relatively high concentration of Ca 2+, Mg 2+, and other divalent cations (soap scum formation.) heat (ph drops) Municipal water-softening operations Water softening by ion exchange Figure Scale formation.

42 Green Chemistry CHAPTER 18.5 GREEN CHEMISTRY 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.

43 CHAPTER 18.5 GREEN CHEMISTRY Green Chemistry Principles 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.

44 CHAPTER 18.5 GREEN CHEMISTRY 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.

45 Green Chemistry CHAPTER 18.5 GREEN CHEMISTRY Toxic and expensive starting materials, high temp, multisteps Less toxic and expensive starting materials, low temp, single step

46 CHAPTER 18.5 GREEN CHEMISTRY Atom economy process A common intermediate used to make polymers

47 CHAPTER 18.5 GREEN CHEMISTRY Atom economy process Click Reaction