Chapter 18 Flashcards
The atmosphere consists of the …
troposphere (up to 10 km), stratosphere (10 – 50 km), and some other “spheres”
Commercial jets fly at 10 km altitude
Combined mass of troposphere and stratosphere is…
99.9 % of the mass of atmosphere
Within the troposphere as altitude increases…
temperature drops down to -50oC at 10 km altitude
As altitude increaes, pressure…
decreases. Pressure drops to 0.26 atm at 10 km and to 0.001 torr at 100 km
Near sea level, the majority of the dry air is…
4:1 N2 and O2 (99% by volume)
Other gases (the remaining 1%) are noble gases, CO2 and CH4:
Argon 0.9% (9000 ppm)
CO2 0.04% (400 ppm)
Neon 0.002% (20 ppm)
Helium 0.0005% (5 ppm)
CH4 0.0002% (2 ppm)
Other gases present in polluted air…
CO: 1 - 50 ppm in urban areas, from incomplete combustion of fuels
NOx: 0.2 ppm in smog
O3: 0.5 ppm in photochemical smog
SO2: 0.1 – 2 ppm in urban areas
Nitrogen is largely…
unreactive due to the bond energy associated with breaking the N ≡ N.
Oxygen has a…
much lower bond enthalpy than nitrogen and is therefore more reactive.
- oxides of nonmetals are…
- oxides of (active) metals are…
- are acidic (Lewis acids)
- are basic
“Outer defense” is
Earth against radiation and high-energy particles occurs beyond the stratosphere and in the stratosphere . More than 50% of harmful radiation is removed before it reaches troposphere
Defensive reaction in the atmosphere
Earth is…
constantly bombarded by high energy radiation (mainly UV) and particles
Atmosphere removes the harmful radiation by…
using it up for photodecomposition of various gases.
Photodissociation is…
rupture of a bond due to absorption of a photon.
Usually radicals (having unpaired electrons) are formed, which are highly reactive.
The most important reaction in the upper atmosphere is…
the photodissociation of oxygen molecules to oxygen atoms. This reaction effectively “removes” from the incoming radiation UV light at wavelengths below 240 nm.
Photodissociation - Earth defense against harmful radiation
Ozone forms from…
the reaction of O2 with O atoms produced in the upper atmosphere by photodissociation of O2 .
The ozone layer occurs…
in the stratosphere, at an altitude of about 25 km.
Bond order in O3 is 1.5…
so bond energy of O3 is lower than that of O2
Ozone absorbs…
much of the radiation between 240 and 310 nm (longer wavelength than O2, protecting us from UV radiation longer than 240 nm).
O2 absorbs shorter UV light (less than 242 nm)
Absorption of radiation leads to…
photochemical decomposition of ozone: O3 + light —> O2 + O
CFCs were used for years as…
aerosol propellants and refrigerants.
The overall result of ozone formation and…
removal reactions throughout billons of years led to the so-called steady state of ozone presence in the stratosphere.
CFCs are not…
not water soluble (do not get washed out of the atmosphere by rain) and are quite unreactive (not degraded naturally), so that eventually they can diffuse to the stratosphere.
In the stratosphere, where the ozone layer exists, the C—Cl bond in CFCs is…
easily broken by light with a wavelength between 190 and 225 nm.
CFCs can reach the stratosphere, b/c at lower altitudes there is not enough of UV radiation present to decompose them.
Chlorine radicals made by photodecomposition of CFCs are..
very reactive. They react with ozone, as shown below:
Cl + O3 —> ClO + O2
ClO is a very…
unstable radical, that can decompose photochemically
Review slide 13; 18-1
Review slide 13; 18-1
The catalyzed decomposition of O3 by Cl radicals from CFCs was theoretically predicted in…
1970s. It was observed experimentally in late 1970s.
In 1987 and 1992 most nations signed the…
Montreal Protocol, in which they agreed to reduce (and eventually stop) production of CFCs. Nobel Prize was awarded to Rowland and Molina from U.C. Riverside in 1995.
As the result of the Montreal Protocol, the Ozone Hole began to…
decrease in size. However, it will take at least 50 years for ozone level in stratosphere to come back to the level from 1970s.
Ozone Hole is…
is the first of four examples for human activities causing harmful changes in Earth’s atmosphere and counteractions developed by research in this area.
four examples of human activities causing harmful changes in Earth’s atmosphere:
Photochemical Smog
Acid Rain
Greenhouse Effect
Ozone Hole
Harmful gases present in the troposphere:
Carbon Monoxide: 10ppm
Hydrocarbons: 3ppm
Sulfur dioxide: .08ppm
Nitrogen oxides: .005ppm
Total oxidants (ozone and others): .02ppm
CO is the…
most abundant harmful gas in urban polluted air.
Although the typical value for SO2 is low…
SO2 is considered the most serious health hazard on the list of most harmful gases present in troposphere
Coal (CxHy) has…
up to 6% of S impurity
Combustion of coal will produce…
then some SO2 gas as a byproduct
SO2 reacts with oxygen and moisture in the air to form…
sulfurous and sulfuric acids.
2 SO2 + O 2 → SO3 (oxidation of SO2 by O2) both gases present
SO2 + H2O → H2SO3 (Lewis A/B reaction, LA + LB → LAdd)
SO3 + H2O → H2SO4 (Lewis A/B reaction, LA + LB → LAdd)
Harmful effects of H+ ions on industrial (and social/art?) infrastructure:
A/B reaction with limestone
2 H+ + CaCO3 → Ca2+ H2CO3 [→CO2 + H2O]
Redox reaction with iron (corrosion)
Fe + 2 H+ → Fe2+ + H2
Uncontaminated rain water has pH of…
5.6
Acid rain has a pH of…
4
The pH of unpolluted water with living organisms is between…
6.5 and 8.5
At pH below 4 most organisms die.
Chemical Method to Prevent SO2 Emissions
from Power Plants:
Powdered limestone is added to the furnace where it decomposes to CaO (lime) and CO2 . CaCO3 + heat → CaO + CO2
Next lime, (CaO) reacts with SO2 by Lewis A/B reaction, removing SO2 from the smokestack. CaO + SO2 → CaSO3
Gases can pass through a suspension of CaO, with the same result.
As the result, in the period 1980 – 2014 the SO2 concentration in air declined by 80%!
Photochemical smog is…
the brownish gas that hangs above large cities.
brown gas is NO2
Source of the photochemical smog:
At 2400 K (in the car cylinders), K for the reaction below is 0.05 (10-15 at 300 K)
N2(g) + O2(g) < ——>(equalbrium) 2 NO(g) (ΔH > 0)
K = 0.05 is not a large number, but leads to some NO present in car exhaust
Smog Chemistry
In air: 2 NO + O2 → 2 NO2 brown gas (absorbs VIS Light)
NO2 + visible light → NO + O
Smog chemistry
O2 + O → O3 (Ozone is very toxic to humans)
O3 is essential in stratosphere but a toxic pollutant in the troposphere
We worry about the ozone hole in the stratosphere and about ozone presence in the troposphere
Catalytic Converter purpose
heterogeneous catalyst to remove NO, CO, and CxHy from car exhaust
Catalytic Converter catalyes two reactions:
oxidation of CO and CxHy (to CO2 and H2O) and reduction of NO to N2
Catalytic Converter:
The exhaust gases spend
less than .5 seconds in the converter.
80% of NO and 95% of CO and CxHy are “removed”
Harmful Human Activity in the Atmosphere #4 :Greenhouse Effect
energy coming in is mainly UV and VIS light, going out is mainly IR (infrared)
Normally energy of radiation coming to Earth equals…
the amount of energy radiated back into space
Water vapor and CO2 in the atmosphere (greenhouse gases)…
help to maintain the atmospheric temperature at night b/c they absorb IR
CO2 levels since the last ice age and industrial revolution (18th century)…
did not change
Last time the level of CO2 was this high (current day) was…
3-5 million years ago
Most climate scientists believe that CO2 increase…
is related to recent climate “changes”.
other gases contribute to greenhouse effect like…
HFCs (replaced CFCs), CH4 (made by bacteria living in swamps, landfills, and cow digestive systems and through leaks during natural gas (CH4/methane)
Since the inductrial revelution, CO2 levels have…
increased since then by 30%, to 400 ppm
Water covers…
72% of Earth’s surface & (like air) it is essential to life
Salt water 97.3 %, oceans, seas, some lakes) pH = 8.0 – 8.3, buffered by HCO3- / CO32-
the ocean is a commercial source of NaCl, Br2 and Mg (both from their salts)
Ice caps 2.1% (huge domes of ice) and glaciers (compacted snow, slowly moving)
Freshwater 0.6% (lakes, rivers, underground)
Freshwater (contains approx. 500 ppm, 0.05% “impurities”)
20% is underground in aquifers “groundwater”
1015 L estimated in U.S. , 1012 L (0.1%) used daily, renewed by rainfall
used in agriculture ( 40%), hydroelectric power (40%), industry (6%), household (6%), drinking (1%)
some groundwater contains toxic chemicals (ex. H3AsO4 in Bangladesh) in the concentration poisonous to humans
Average US adult uses…
2L of drinking water per day; 300L for persoal consumption and hygiene per day
sub-Saraha Africa human water use
30L of water per day
Seawater has too high a concentration of
NaCl for human consumption.
It can be desalinated through reverse osmosis.
Osmosis:
water naturally flows through a semipermeable membrane from regions of low salt concentration to regions of high salt concentration
Osmotic pressure
is defined as the pressure needed to stop osmosis.
Osmosis can be reversed if…
the pressure higher than osmotic pressure is applied.
During reverse osmosis water moves from more concentrated to more diluted solution, desalinating the see water.
Semipermeable membrane is in the shape of…
hollow fibers
Saline water is added under pressure into the space between the fibers
Desalinated water is recovered from inside the hollow fibers
Water fully saturated with air has…
10 ppm of dissolved oxygen, fish require 5 ppm dissolved oxygen for survival
The amount of O2 in water is an important indicator of…
Water quality
Excessive amounts of biodegradable matter can result in…
inability of normal animal life to exist, b/c when aerobic bacteria act on biodegradable matter, they use oxygen.
inability of normal animal life to exist, b/c when aerobic bacteria act on biodegradable matter, they use oxygen.
sewage, waste from food processing plants, paper mills, and meat packing plants
Excessive plant nutrients (fertilizers) in waste can lead to…
eutrophication, or excessive dead plant matter in water.
It can also lead to anaerobic oxidation conditions, which give off bad odors, (NH3, PH3, H2S)
Five Steps of Municipal Water Treatment
Water coming into municipal water system is “used” water and needs to be treated before we use it at home
Coarse filtration through a screen.
Sedimentation tanks (with spongy gelatinous Al(OH)3 [from Al3+ salts and OH- ions]). As Al(OH)3 settles slowly down, carries small particles and most bacteria with it.
“Finer” filtration through a sand bed.
Aeration (water sprayed into air) to dissolve more O2 needed to oxidize some toxic ions, kill more bacteria, and reduce concentration of other volatile compounds (H2S, NH3)
Sterilization (Cl2 or O3)
Sterilization defination
has dramatically lowered the incidence of waterborne diseases (cholera, typhus)
Ozone or Chlorine?
Both have advantages and disadvantages
Cl2 disproportionates in water (ox & red) (ox: HClO red: HCl)
HClO reacts with organic matter making THMs (what are they?),
O3 can oxidize Br to BrO3- which is carcinogenic for rats
Choices must be made considering risk & benefit
Water situation in the world:
One billion people lack access to clean water
95% of the world’s cities dump raw sewage into their water supply.
85% of health problems in developing countries are directly related to unsanitary water
