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Transcript
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. 1 PDF created with FinePrint pdfFactory Pro trial version http://www.pdffactory.com 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. 2 PDF created with FinePrint pdfFactory Pro trial version http://www.pdffactory.com 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) 3 PDF created with FinePrint pdfFactory Pro trial version http://www.pdffactory.com 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. 4 PDF created with FinePrint pdfFactory Pro trial version http://www.pdffactory.com 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! 5 PDF created with FinePrint pdfFactory Pro trial version http://www.pdffactory.com 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 6 PDF created with FinePrint pdfFactory Pro trial version http://www.pdffactory.com 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 7 PDF created with FinePrint pdfFactory Pro trial version http://www.pdffactory.com 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 8 PDF created with FinePrint pdfFactory Pro trial version http://www.pdffactory.com 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? 9 PDF created with FinePrint pdfFactory Pro trial version http://www.pdffactory.com 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 10 PDF created with FinePrint pdfFactory Pro trial version http://www.pdffactory.com