Class objectives:

1
Class objectives

• Highlight some important areas in environmental
  chemistry
• present some of the common techniques that
  environmental chemists use to quantify process
  that occur in the environment
• It is assumed that everyone has courses in
  calculus and general chemistry.

2
Class objectives

• We will cover general topics Global warming,
  Strat. O3, aerosols, photochemical smog, acid
  rain, etc.
• Develop relationships will be used to help
  quantify equilibrium and kinetic processes

3
Important Environmental Issues

• Global warming and stratospheric ozone depletion
• Concentration of environmental pollutants at the
  poles pesticides in foods, etc.
• Buildup of environmental chemicals in the oceans
  contamination of soil and ground water
• Particle exposure, photochemical oxidant
  exposure, acid deposition
• Energy shortages

4
Energy from the earth
54.4x1020 kJoules of the suns energy strikes
the earths surface each year
Sun
earth

• Of this 30 is reflected back to into space
  (albedo)
• One Joule 4.2 calories. It takes 2000 K-
  calories to feed a human each day
• What fraction of the earths energy striking the
  earth, if turned into food, could feed the planet
  

5
Where are the global energy reserves
oil
Figure 1.5 Spiro page 10
Former USSR
Middle East
Asia and Australia including China
6
Fraction of US oil reserves compared to the
global total (British petroleum web site, 2007)
7
The atmospheric compartment

• How much does it weigh?
• Temperature and pressure
• Circulation and mixing
• Where did Oxygen come from
• Particle emissions
• Emissions of other pollutants

8
How thin is the air at the top of Mt. Everest?

• Mt. Everest is 8882 meters high or 8.88 km high
• log P -0.06 x 8.88
• P 10-0.06x 8.88 0. 293 bars
• Assume there are 1.01bars/atm.
• This means there is lt 1/3 of the air

9
The quantity ?d is called the dry adiabatic lapse
rate

• ?d - dT/dz 9.8 oK/kilometer
• If the air is saturated with water the lapse rate
  is often called ?s
• Near the surface ?sis -4 oK/km and at 6 km and
  5oK/km it is -6K/km at 7km high

10
Mixing height in the morning
11
What is Global Warming and how can it Change the
Climate?
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1979 perennial Ice coverage Nat. Geographic, Sept
2004)
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2003 perennial Ice coverage
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Per Capita CO2 Emissions
6
5
4
3
Metric Tonnes per year
2
1
0
US
Canada
Germany
World-avg
India
Australia
Russia
Japan
China
16
Kinetics   1st order reactions
A ---gt B   -d A /dt krate A   - d
A/A kratedt     At A0 e-kt
17
Some time vs conc. data
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A plot of the lnconc vs. time for a 1st order
reaction gives a straight line with a slope of
the 1st order rate constant.
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ln A/Ao-k t1/2 ln2 /k t1/2
2nd order reactions A B ? products dA/dt k2nd
AB If B is constant kpseudo 1st k2nd
B
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kpseudo 1st k2nd B ln2 /k t1/2 1. constant
OH radicals in the atmosphere kpseudo 1st k2nd
OH. 2. constant pH kpseudo 1st k2nd OH-
21
The Hammett Equation and rates constants
DGo DGoH S DGoi
log Ka log KaH Ssi   so, log (Ka / KaH )
SsI and pKa pKaH - SsI
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It is also possible to show that   log(krate)
log krateH r sm,p   or log(krate/krateH)
r sm,p
25
What this means is for aromatics with different
substituted groups, if we know the r value we can
calculate the rate constant from the sigma (sm,p)
and the hydrogen substituted rate constant.   If
we know the rate constant for a number of similar
aromatics with different substituted groups, we
can create a ymxb plot and solve for the slope
r value (see example at end of Pesticide Chapter)
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ln A/Ao-k t1/2 ln2 /k t1/2
2nd order reactions A B ? products dA/dt k2nd
AB If B is constant kpseudo 1st k2nd
B
27
Using fugacities to model environmental systems
(Donald Mackay EST, 1979)Consider the phase
equilibrium of five environmental compartments.
Is it possible to tell where an environmental
pollutant will concentrate? where A air,
B lake, C Soil, D Sediment, E biota and
suspended solids
Thermodynamics How do the pollutants in the
different compartments of the environment
distribute?
A
B
C
C
D
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fA fB fC fD fE
Fugacities can be translated into
concentrations fi Zi C
In Air piV nRT, pi Cair RT, so Ziair
1/RT
In water Ziw pi /fw KH 1/KH
Remember we also used Henrys law to calculate
how fast the atmosphere cleans up, and in another
problem fractions of a toxic in the gas and water
phase of a flask
In biota ZB B ? y ? Kiow/KiH
Remember octanol/water partitioning coef. to
calculated bio accumulation factors.
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We looked at the Equilibrium Distribution of a
toxic compound with an atmospheric concentration
of 4 x 10-10 mol/m3.(fi x Zi C and Mi fi Zi
Vi)   Z Vol fi M mg/m3. (m3) (atm) (moles)  
air 40 1010 10-11 4 0.35 water 104 106 10-11 10-
1 0.01 10-5s solids 103 106 10-11 10-2 0.001 0.01
Sed 109 104 10-11 102 9.1 0.05Soil 109 105 10-11
103 90.5 0.5Aq biota 104 106 10-11 10-1 0.01 0.
2
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How are the different thermodynamic parameters
related?
mig moig RT ln pi/poi
mi moi RT ln fi/ foi
for ideal liquids p1i x1 piL and p2i x2
piL
for non-ideal liquids
fiL ?i XipiL (pure liquid)
fi hx fi H2O
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Obtained the important result giH2O1/ Xi H2O
Ci Xi / molar volumemix
the VH2O 0.0182 L/1 mol
Vmix S Xi Vi
typically organics have a Vi of 0.1 L/mol Vmix
? 0.1 Xi 0.0182 XH2O
MW/density can be used to estimate molar volume.
For most organic compounds if you do not know the
density, assume 1 g/ml.
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From the saturated concentration of an organic in
water (Ciwsat) can you calculate the mole
fraction and activity coefficient? Remember the
toluene homework where you were given a maximum
saturation concentration in water of 515
mg/liter H2O. Convert this to moles per liter
which is a Ciwsat . Ciwsat mole fraction/molar
vol.
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It is also possible to estimate estimated Csatiw
from molar volumes ln Csatiw -a (size) b
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Henrys law sat. vapor pressure/ (Ciwsat)
Sat. Vapor pressure (p iL) can be calculated
from Tb (boiling points and entropy of
vaporization Tb 198 S funtional groups
log Kiow -a log Csatiw b a
b r2 hAlkanes 0.85 0.62 0.98 hPAHs 0.75 1.
17 0.99 h alkylbenzenes 0.94 0.60 0.99
chlorobenzens 0.90 0.62 0.99 hPCBs 0.85 0.78
0.92 hphthalates 1.09 -0.26
1.00 hAlcohols 0.94 0.88 0.98 h
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Bioaccumulation and octanol water, Kiow
Moli/ml water is the concentration of a toxic in
the water phase (Ciw)
Henrys law partial pressure i/ (Ciw)
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Go over problems I did at the board, problems
that were covered from the notes during class,
and homework problems from the short and long
homework sets. Look at the natural waters
homework/with answer link The exam will cover
thermo, vapor pressure, henrys law, water
octanol, surface and water purification,
pesticides and heavy toxic metals. It will have
problems and some short questions. Good luck to
all