Chemistry in Context:Chapter 3:The Chemistry of

Global WarmingPractice Problems:All Ch. 3 problems with the blue codes or answers on Page 521.

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.

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.

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.

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 on Page 101Fig. 3.2 Page 101

Figure 3.4 page 103

Earth = 15 °C

Outer Space = -270 °CEnergy 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, CH4, and others are increase in concentration, leading to >84% heat returned to Earth, thereby raising the Earth’s average temperature

Figure 3.5 page 104

Mauna Loa

Global Temperature Trends• 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.

Figure 3.6 Page 105 Lewis Structures and Molecular Shapes• 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 (decreasing repulsion→)

Methane (CH4) vs. CFC-11

•Tetrahedral•4 bp & 0 lp•Non-polar CH4•Slightly polarCFC-11

Fig. 3.8 Pg. 108

Figure 3.9 Page 109

•Ammonia (NH3) -Triangular pyramid•Lone pair on N pushes 3 bonding pairs, N-H, downward.

H-O-H angle = 104.5°Water (H2O) has 2 lp & 2 bpShape = bent or angular

Figure 3.10 Pg. 109CO2-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

•CO2 absorbs IR photons with its energy being promoted from ground state to excited state.•Different molecular vibrational modes have different energy.

Fig. 3.14 Figure 3.14 page 113:Figure 3.14 page 113:IR Spectrum of COIR Spectrum of CO22

Fig. 3.15 Page 113Water vapor SpectrumWavenumber =1/λ

Interaction between Energy and Matter

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

CO2 output = CO2 input? Fossil Fuel contribution

Pg. 116

Pg. 117

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 USFigure 3.17, Page 117

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!

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.

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.

Example Continued• 15.9994 g oxygen =6.02 x 1023 oxygen atoms

2.66 x 10-23 g oxygenoxygen atom

• Practice 3.19 Your Turn on Page 121 for the mass of a nitrogen atom and five trillion atoms.

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. stoichiometriccoefficients).

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.

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

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!

Table 3.4 on Page 125

Methane in Ice Deposit from Ocean Floor

Figure 3.19 Page 126Nitrous oxide

• N2O or “laughing gas” is used as inhaled 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

Table 3.5 on Page 126

Greenhouse factor is a value that represents the relative contribution of a molecule of a substance to global warming.

Climate Modeling• Many factors are involved; examples include

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 Table 3.7 Page 131

Figure 3.22 Page 130 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.

Fig.

3.24

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Blue - ↓Red - ↑

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. 3.20 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