Download The Chemistry of Global Warming

Venus
The Chemistry of
Global Warming
• Atmospheric pressure is 90x that of Earth
• 96% CO2 and sulfuric acid clouds
• Average temperature = 450 °C
• Expected temperature based on solar
radiation and distance from sun is 100 °C
• Possibility of CO2 absorbing infrared
radiation and trapping solar heat in the
atmosphere.
Earth
• 78% N2 and 21% O2
• Less than 1% other gases
• Average temperature = 15 °C
• Expected temperature based on solar
radiation and distance from sun -18 °C
• 33 °C warmer than expected; hence no
frozen oceans and life flourishes.
• Water vapor and CO2 play a role in
trapping solar radiation in the form of
heat.
More History
• Early atmosphere: 1000x CO2?
• CO2 trapped heat that warmed up Earth
to allow life to develop 3 billion years
– primitive plants (e.g. cyanobacter) carry out
photosynthesis with light-capturing chlorophylls
– 6 CO2 + 6 H2O + hν → C6H12O6 + 6 O2
– Availability of O 2 allowed the evolution of animals
– Earth temperature is 10-15 °C higher 100 million
years ago.
History of Global Warming
• Fourier (1800): proposed “hothouse” or
“greenhouse” effect.
• Tyndall (1860): demonstrated CO2 and H2O
absorb heat
• Is there any correlation among the following 3
known facts.
– CO2 absorbs heat
– Concentration CO2 in atmosphere is
increasing
– Earth’s average temperature is NOT constant
Evidence for CO2 Warming
• Drilled cores from ocean floors
– Microorganisms → temperature.
– Magnetic field in sediment → time
• Antarctic ice cores provided ratios of
deuterium to hydrogen (2H/1H) and CO2
levels for past 160 millennia.
– Light 1H2O evaporates faster than heavy 2H2O,
leading to the enrichment of heavy water in the
ocean relative to the atmosphere.
– During years of warmer temperatures, more heavy
water escapes to the atmosphere that return to
Earth as snow or rainfall; hence, higher 2H/1H
implies higher temperature.
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Fig. 3.1
Page 97
Fig. 3.2
Figure 3.2 page 99
Outer Space = -270 °C
Energy Balance
• ~ 84% heat radiated by Earth is
absorbed by gases in atmosphere
• Re-radiated back to Earth in the form
of “GREENHOUSE EFFECT”.
• Greenhouse gases include CO2 , H2O,
Earth = 15 °C
CH4, and others are increase in
concentration, leading to >84% heat
returned to Earth, thereby raising the
Earth’s average temperature
Global Temperature Trends
Mauna Loa
Figure 3.3 page 100
• The Earth’s temperature increased an
average of 0.6 °C from 1880 to 2000;
but this may be a short term fluctuation
since 120 years are short in comparison
to the 4.5 billion history of the Earth.
• Doubling CO2 levels will increase
temperature by 1.0-3.5 °C , smaller than
Arrhenius’s prediction of 5-6 in 1896.
• Absorption of infrared radiation depends
on molecular vibrations.
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Lewis Structures and Molecular Properties
• Prediction of molecular shapes and properties
from Lewis structures.
• Octet Rule requires that each atom has 8 or
4 pairs of electrons; either bonding pairs (bp)
and lone pairs (lp).
• Molecular geometry is determined by the
number of lp and bp as well as the nature of
electronic interaction:
lp-lp>lp-bp>bp-bp (increasing repulsion→)
Methane (CH4) vs. CFC-11
Fig. 3.9
•Ammonia (NH3) -Triangular pyramid
•Lone pair on N pushes 3 bonding
•Tetrahedral
•4 bp & 0 lp
•Non-polar CH4
•Slightly polar
CFC-11
H-O-H angle = 104.5°
Water (H2O) has 2 lp & 2 bp
Shape = bent or angular
pairs, N-H, downward.
CO2 - Linear with double bonds
O3 has resonance forms (mixed single and
double bonds)
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Greenhouse Gases
• CO2 linear
• CH4 tetrahedron
• H2O bent
• CFCs tetrahedron
• NH3 triangular pyramid
• 3.7 Your Turn page 104
• 3.8 Your Turn page 105
Page 106
Infrared (IR) Absorption by Molecules
• Bonds absorb IR radiation that result in
a change of the vibrational frequency;
but IR is not energetic enough to cause
bond dissociation.
• The specific vibrational frequency for
the absorption occurs is measured by an
IR spectrometer.
• The plot of radiation intensity or
absorbance vs. λ is known as an IR
spectrum.
Fig. 3.14
Figure 3.6 page 106:
IR Spectrum of CO2
•CO2 absorbs IR photons with its energy being
promoted from ground state to excited state.
•Different molecular vibrational modes have different
energy.
Interaction between Energy and Matter
Fig. 3.7 Page 107
Water vapor Spectrum
Wavenumber =1/λ
Spectrum of energy absorption provides
information about the nature of molecular
structure and is used to identify and
quantify chemical compounds.
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Carbon Cycle Figure 3.9 page 108
•CO2 output = CO2 input? Fossil Fuel contribution
Carbon Cycle
• Sink: natural storage place in
environment that removes C from
another part of cycle
• Flux: amount of C moving in the
environment in 1 year
• Net gain of CO2 in atmosphere is about
3.1 to 3.5 Gt (gigaton) per year.
• Excess CO2 results in an increase of 1.5
ppm per year
CO2 Emission sources in US
Figure 3.10, Page 109
Mass Number
• The sum of the number of protons
and the number of neutrons for a
specific atom of an element is called
mass number
• Mass number is not the same as
atomic mass!
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Avogadro’s Number
• 6.02 x 1023
• 1 mole = 6.02 x 1023 atoms,
molecules, or charged particles
• Mole is a unit for counting atoms,
molecules, ions, electrons, very
small particles
Atomic Mass
• Each element has a unique atomic mass.
• Atomic mass is defined as the average mass
•
•
•
•
of an atom of that element as compared to
an atomic mass of exactly 12 amu for a 12C
atom
Atomic mass unit = amu
1 amu = 1.66 x 10-24 gram
Atomic mass unit (amu) is too small to
measure using balances
∴Laboratory measurements of mass are
reported in grams
Example
Example cont.
• What is the mass of 1 oxygen atom?
• Units: g oxygen/oxygen atom
• Atomic mass is 15.9994 grams of
• 15.9994 g oxygen =
oxygen per mole of oxygen atoms
• 1 mole contains 6.02 x 1023 oxygen
atoms
• Divide!
6.02 x 1023 oxygen atoms
2.66 x 10-23 g oxygen
oxygen atom
• Practice 3.12 Your Turn
Chemical Reaction & Moles
• C + O2 → CO2
• Number of atoms and molecules
in a reaction are proportional to
the number of moles of the same
substances
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Molar Mass
• The mass of one Avogadro’s number
Example
of whatever particles (atoms or
molecules) are specified.
• Mass for 1 mole of atoms of an
element is given in grams in the
Periodic Table.
• Mass for 1 mole of molecules is
obtained by adding the masses of all
the elements constituting the
compounds.
• NH3
• Find atomic mass for each atom
Example cont.
Methane
• But we have 3 hydrogen atoms
• 3 x 1.008 g = 3.024 g of hydrogen
• For NH3, add the mass of nitrogen to
• CH4
• “Cow gas”
• 30x better than CO2 in trapping
that of hydrogen! 3.024 g + 14.01 g
= 17.034 g
• Molar mass of NH3 = 17.034 g per
mole of NH3
• 3.13, 3.14, 3.15 Your Turn
Table 3.1 on Page 118
in the molecule
• N 14.01 g
• H 1.008 g
IR
• But there is less CH4 in the
atmosphere!
CH4
• Natural gas
• Petroleum refining
• Decaying vegetable matter
• Agriculture
• Cows! 500 L per day
• Termites
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Nitrous oxide
• N2O
• Laughing gas
• Synthesized fertilizers
• Burning of biomass
• Agriculture
• Also plays role in O3 depletion
Methane in Ice Deposit
Table 3.2 on Page 119
Modeling
• Many factors are involved
• Difficult to isolate one factor
• Computers used to project “what
if” scenarios
Greenhouse factor is a value that represents
the relative contribution of a molecule of a
substance to global warming.
• IPCC Intergovernmental Panel of
Climate Change
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Enhanced Greenhouse
• Is the average temperature of
Earth increasing because of
human activities?
• Yes
IPCC Report
• CO2 and other greenhouses gases contributes
to an elevated global temperature.
• The concentration of CO2 has been increasing
over the past 100 years.
• Increase of atmospheric CO2 is a result of
human activity.
• Average global temperature has increased
over the last 100 years.
What now?
• Modeling results indicate coming
climate changes
• Reduce reliance on fossil fuels
• What else?
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Kyoto Protocol
• Global conference in 1997 to reduce
emissions of greenhouse gases to
“acceptable” levels
• Developing countries versus
industrialized countries
• 2001, USA did not “sign”
• But USA accounts for 25% of
emissions…
Which is Worse?
• Global warming
• O3 depletion
• Table 3.3
• Defend your position with facts
• 1 FULL page report, typed
Practice
• 1-3, 6, 9, 10, 14-18, 20, 21, 24,
25, 29, 36-39, 41, 50
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