Download Chemistry in Context: Chapter 3:The Chemistry of Global Warming

Chemistry in Context:
Chapter 3:The Chemistry of
Global Warming
Practice Problems:
All Ch. 3 problems with the blue
codes or answers on Page 521.
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.
Venus
• 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.
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
History of Global Warming-2
• 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 O2 allowed the evolution of animals
– Earth temperature is 10-15 °C higher 100 million
years ago.
Fig. 3.2 on Page 101
Evidence for CO2 Warming
• Drilled cores from ocean floors
– Microorganisms → temperature.
– Magnetic field in sediment → time
• Antarctic ice cores provided ratios of (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.
Fig. 3.2 Page 101
Energy Balance
Figure 3.4 page 103
Outer Space = -270 °C
Earth = 15 °C
• ~ 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,
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
• The Earth’s temperature increased an average of
Figure 3.5 page 104
•
•
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.
Figure 3.6 Page 105
Lewis Structures and Molecular Shapes
• Prediction of molecular shapes and properties
•
•
Methane (CH4) vs. CFC-11
•Tetrahedral
•4 bp & 0 lp
•Non-polar CH4
•Slightly polar
CFC-11
Fig. 3.8 Pg. 108
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 (decreasing repulsion→)
Figure 3.9 Page 109
•Ammonia (NH3) -Triangular
pyramid
•Lone pair on N pushes 3 bonding
pairs, N-H, downward.
Figure 3.10 Pg. 109
H-O-H angle = 104.5°
Water (H2O) has 2 lp & 2 bp
Shape = bent or angular
CO2-Linear with double bonds
O3 has resonance forms (mixed
single and double bonds)
Fig.
3.11
Pg.
110
Fig.
3.12
Pg.
111
Greenhouse Gases
• CO2 linear
• CH4 tetrahedron
• H2O bent
• CFCs tetrahedron
• NH3 triangular pyramid
• 3.9 Your Turn page 110
• 3.10 Your Turn page 111
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.
Figure 3.13 Page 112
Fig. 3.14
Figure 3.14 page 113:
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. 3.15 Page 113
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.
(Fig. 3.16 Pg. 114)
Carbon Cycle Figure 3.13 page 115
Pg. 116
CO2 output = CO2 input? Fossil Fuel contribution
Carbon Cycle
Pg. 117
• 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
Mass Number
• The sum of the number of protons and
CO2 Emission sources in US
Figure 3.17, Page 117
Avogadro’s Number
• Avogadro’s Number = 6.02 x 1023
• 1 mole = 6.02 x 1023 atoms,
molecules, or charged particles
• Mole is a convenient unit for counting
very small particles contained in gram
quantities of chemical substances.
the number of neutrons for a specific
atom of an element is called mass
number
• Mass number is not the same as
atomic mass!
Atomic Mass of Elements
• 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 can be measured by units of atomic
mass unit (amu) or grams per mole.
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: Mass of an Atom
• What is the mass of 1 oxygen
atom expressed in grams?
• Atomic mass is 15.9994 grams of
oxygen per mole of oxygen atoms
• Since 1 mole contains 6.02 x 1023
oxygen atoms, atomic mass
divided by Avogadro Number gives
the mass of one oxygen atom.
Chemical Reaction & Moles
• C + O2 → CO2
• The numbers of atoms and molecules
involved in a reaction are proportional
to the number of moles of the
substances expressed in a balanced
chemical equation (i.e. stoichiometric
coefficients).
Example Continued
• 15.9994 g oxygen =
6.02 x 1023 oxygen atoms
2.66 x 10-23 g oxygen
oxygen atom
• Practice 3.19 Your Turn on Page 121 for
the mass of a nitrogen atom and five
trillion atoms.
Page 122
Molar Mass
• The mass of one Avogadro’s number
(i.e. 1 mole) of molecular formula
units of a chemical compound
expressed in grams.
• Molar mass is calculated by
summing the atomic masses
according to the molecular formula.
Methane
• CH4 in natural gas is an important
greenhouse gas.
• CH4 is produced in cattle farming, rice
growing, petroleum refining, termite
mounds, and landfills.
• 30 times more efficient than CO2 in
trapping IR
• But there is less CH4 (~1.8 ppm) than
CO2 (~370 ppm) in the atmosphere!
Example: Molar Mass Calculation
• What is the molar mass of NH3?
• Find atomic mass for 1 mole of each atom
in the molecule: N=14.01 g; H=1.008 g
• For NH3, add the mass of nitrogen to that
of hydrogen! (3 x 1.008) g + 14.01 g =
17.034 g
• Molar mass of NH3 = 17.034 g per mole of
NH3
• Mass of one NH3 molecule = 17.034 amu
Table 3.4 on Page 125
Figure 3.19 Page 126
Nitrous oxide
• N2O or “laughing gas” is used as inhaled
•
•
•
Methane in Ice Deposit
from Ocean Floor
Table 3.5 on Page 126
dental/medical anesthetic.
Anthropogenic sources of N2O are synthesized
fertilizers and burning of biomass.
Agriculture exacerbates N2O problem.
Also plays a role in O3 depletion, which has a
cooling effect in the stratosphere
Climate Modeling
• Many factors are involved; examples include
•
•
Greenhouse factor is a value that represents the
relative contribution of a molecule of a
substance to global warming.
•
solar radiation, wind patterns, cloud cover,
volcanic activity, dust and soot, ocean currents,
and living things.
Intertwined factors make it difficult to study and
the effect of CO2 independently.
Computers are used to project “what if”
scenarios.
IPCC (Intergovernmental Panel of Climate
Change) reaffirms the role of CO2 in warming.
Figure 3.21 Page 129
Figure 3.22 Page 130
Table 3.7 Page 131
Fig. 3.23
Page 132
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.
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…
Fig.
3.24
Pg.
134
Blue - ↓
Red - ↑
Fig. 3.20
Fig. 3.25
Fig.
3.26
Pg.
140
Debate Topic: Stratospheric Ozone
Depletion Vs. Global Warming
• Based on what you have learned
regarding global warming and ozone
depletion, determine which is a more
serious environmental threat.
• Refer to Table 3.8
• Defend your position with facts