The Chemistry of Global Warming Venus Atmospheric pressure is 90x that of Earth 96% CO 2 and sulfuric acid clouds Average temperature = 450 C Expected temperature based on solar radiation and distance from sun is 100 C Possibility of CO 2 absorbing infrared radiation and trapping solar heat in the atmosphere. Earth 78% N 2 and 21% O 2 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 CO 2 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 CO 2 and H 2 O absorb heat Is there any correlation among the following 3 known facts. CO 2 absorbs heat Concentration CO 2 in atmosphere is increasing Earth s average temperature is NOT constant More History Early atmosphere: 1000x CO 2? CO 2 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 CO 2 + 6 H 2 O + hν C 6 H 12 O 6 + 6 O 2 Availability of O 2 allowed the evolution of animals Earth temperature is 10-15 C higher 100 million years ago. Evidence for CO 2 Warming Drilled cores from ocean floors Microorganisms temperature. Magnetic field in sediment time Antarctic ice cores provided ratios of deuterium to hydrogen ( 2 H/ 1 H) and CO 2 levels for past 160 millennia. Light 1 H 2 O evaporates faster than heavy 2 H 2 O, 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 2 H/ 1 H implies higher temperature. 1
Fig. 3.2 Fig. 3.1 Page 97 Figure 3.2 page 99 Earth = 15 C 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 CO 2, H 2 O, CH 4, and others are increase in concentration, leading to >84% heat returned to Earth, thereby raising the Earth s average temperature Mauna Loa Figure 3.3 page 100 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 CO 2 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
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 (CH 4 ) vs. CFC-11 Tetrahedral 4 bp & 0 lp Non-polar CH4 Slightly polar CFC-11 Fig. 3.9 Ammonia (NH 3 ) -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 bp Shape = bent or angular CO 2 -Linear with double bonds O 3 has resonance forms (mixed single and double bonds) 3
Greenhouse Gases CO 2 linear CH 4 tetrahedron H 2 O bent CFCs tetrahedron NH 3 triangular pyramid 3.7 Your Turn page 104 3.8 Your Turn page 105 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. Page 106 Fig. 3.14 Figure 3.6 page 106: IR Spectrum of CO 2 CO 2 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
Carbon Cycle Figure 3.9 page 108 CO 2 output = CO 2 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 CO 2 in atmosphere is about 3.1 to 3.5 Gt (gigaton) per year. Excess CO 2 results in an increase of 1.5 ppm per year CO 2 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
Avogadro s Number 6.02 x 10 23 1 mole = 6.02 x 10 23 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 12 C 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 What is the mass of 1 oxygen atom? Units: g oxygen/oxygen atom Atomic mass is 15.9994 grams of oxygen per mole of oxygen atoms 1 mole contains 6.02 x 10 23 oxygen atoms Divide! Example cont. 15.9994 g oxygen = 6.02 x 10 23 oxygen atoms 2.66 x 10-23 g oxygen oxygen atom Practice 3.12 Your Turn Chemical Reaction & Moles C + O 2 CO 2 Number of atoms and molecules in a reaction are proportional to the number of moles of the same substances 6
Molar Mass The mass of one Avogadro s number 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. Example NH 3 Find atomic mass for each atom in the molecule N 14.01 g H 1.008 g Example cont. But we have 3 hydrogen atoms 3 x 1.008 g = 3.024 g of hydrogen For NH3, add the mass of nitrogen to that of hydrogen! 3.024 g + 14.01 g = 17.034 g Molar mass of NH 3 = 17.034 g per mole of NH 3 3.13, 3.14, 3.15 Your Turn Methane CH 4 Cow gas 30x better than CO 2 in trapping IR But there is less CH 4 in the atmosphere! Table 3.1 on Page 118 CH 4 Natural gas Petroleum refining Decaying vegetable matter Agriculture Cows! 500 L per day Termites 7
Nitrous oxide Methane in Ice Deposit N 2 O Laughing gas Synthesized fertilizers Burning of biomass Agriculture Also plays role in O 3 depletion Table 3.2 on Page 119 Greenhouse factor is a value that represents the relative contribution of a molecule of a substance to global warming. Modeling Many factors are involved Difficult to isolate one factor Computers used to project what if scenarios IPCC Intergovernmental Panel of Climate Change 8
Enhanced Greenhouse Is the average temperature of Earth increasing because of human activities? Yes IPCC Report CO 2 and other greenhouses gases contributes to an elevated global temperature. The concentration of CO 2 has been increasing over the past 100 years. Increase of atmospheric CO 2 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
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 O 3 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