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Chapter 3: Global Warming

Chapter 3: Global Warming. The Earth’s Energy Balance. Greenhouse effect Our atmospheric gases trap and return a major portion of the heat radiating from the Earth. 3.1. CO 2 Concentration vs. Earth’s temperature. 3.2. Atmospheric CO 2 level on the rise. 3.2.

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Chapter 3: Global Warming

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  1. Chapter 3: Global Warming

  2. The Earth’s Energy Balance Greenhouse effect Our atmospheric gases trap and return a major portion of the heat radiating from the Earth. 3.1

  3. CO2 Concentration vs. Earth’s temperature 3.2

  4. Atmospheric CO2 level on the rise 3.2

  5. Review: How to draw Lewis structures Draw Lewis Structures for: O2 CH4 SO2 C2H4 SO42- CO H2SO4 N2----------------------------------NO3- O3 1. Determine the sum of valence electrons • Use a pair of electrons to form a bond • between each pair of bonded atoms • Arrange the remaining electrons to • satisfy octet rule (duet rule for H) 4. Assign formal charges Formal charge = # of v.e. – [# of non-bonding e- + ½ bonding e-] or, F.C. = # of v.e. – [# of bonds to the atom + # non-bonding e-] Remember: Resonance, relative lengths and bond order! 3.3

  6. Representations of methane CH4 = molecular formula; does not express connectivity Structural formulas show how atoms are connected: Space-filling Charge- density Lewis structures show connectivity This Lewis structure is drawn in 3-D 3.3

  7. The 3-D shape of a molecule affects ability to absorb IR radiation. Valence Shell Electron Pair Repulsion Theory Assumes that the most stable molecular shape has the electron pairs surrounding a central atom as far away from one another as possible 3.3

  8. Valence Shell Electron Pair Repulsion Theory Consider methane (CH4), where the central carbon atom has 4 electron pairs around it: A tetrahedral shaped molecule has bond angles of 109.5o. Four electron pairs as far from each other as possible indicates a tetrahedral arrangement. 3.3

  9. Valence Shell Electron Pair Repulsion Theory The legs and shaft of a music stand are like the bonds of a tetrahedral molecule. 3.3

  10. The central atom (O) in H2O also has four electron pairs around it, The non-bonding electron pairs take up more space than bonding pairs, so the H-to-O-to-H bond angle is compressed. but unlike methane, two electron pairs are bonding and two are non-bonding. The electron pairs are tetrahedral arranged, but the shape is described only in terms of the atoms present: water is said to be bent shaped. 3.3

  11. We can use the VSEPR model to allow us to predict the shape of other molecules. Other predictions can be made based on other electron pair arrangements . 3.3

  12. Now look at the central atom of CO2: Two groups of four electrons each are associated with the central atom. The two groups of electrons will be 180o from each other: the CO2 molecule is linear. 3.3

  13. Molecular geometry and absorption of IR radiation Molecular vibrations in CO2. Each spring represents a C=O bond. (a) = no net change in dipole - no IR absorption. (b, c, d) = see a net change in dipole (charge distribution), so these account for IR absorption 3.4

  14. The infrared spectrum for CO2 As IR radiation is absorbed, the amount of radiation that makes it through the sample is reduced 3.4

  15. The infrared spectrum for CO2 Wavenumber (cm-1) =10,000 wavelength (mm) 3.4

  16. Molecular response to different types of radiation 3.4

  17. The carbon cycle 3.5

  18. Mole: SI definition: the number equal to the number of carbon atoms in exactly 12 g of pure C-12. Atomic number Avogadro’s number is 6.022 x 1023 Mass number A mole of atoms of any element has a mass (in grams) equal to the atomic mass of the element in amu. The carbon cycle 3.7

  19. 6.022 x 1023 Atomic number One mole of carbon has a mass of 12.01 grams; 1 mol C = 12.01 g Mass number If you have 36.03 g of carbon, how many moles is that? 1 mol C 36.03 g C x = 3.0 mol C 12.01 g C The carbon cycle 3.7

  20. Keep these relationships in mind: use molar mass grams use Avogadro’s number molecules moles Remember – the critical link between moles and grams of a substance is the molar mass. IT’S SIMPLE – THINK IN TERMS OF PARTICLES! 3.7

  21. CO2 emission sources from fossil fuel consumption Deforestation contributes another 1-2 bmt/year 3.5

  22. Amplification of Greenhouse Effect: Global Warming: What we know 1. CO2 contributes to an elevated global temperature. 2. The concentration of CO2 in the atmosphere has been increasing over the past century. 3. The increase of atmospheric CO2 is a consequence of human activity. 4. Average global temperature has increased over the past century. 3.2

  23. What might be true: 1. CO2 and other gases generated by human activity are responsible for the temperature increase. 2. The average global temperature will continue to rise as emissions of anthropogenic greenhouse gases increase. 3.9

  24. 3.2

  25. Loss of Polar Ice Cap NASA Study: The Arctic warming study, appearing in the November 1 2003 issue of the American Meteorological Society's Journal of Climate, showed that compared to the 1980s, most of the Arctic warmed significantly over the last decade, with the biggest temperature increases occurring over North America. 1979 2003 Perennial, or year-round, sea ice in the Arctic is declining at a rate of nine percent per decade. 3.9

  26. Loss of Polar Ice Cap 1979 As the oceans warm and ice thins, more solar energy is absorbed by the water, creating positive feedbacks that lead to further melting. Such dynamics can change the temperature of ocean layers, impact ocean circulation and salinity, change marine habitats, and widen shipping lanes. 2003 3.9

  27. The snows of Kilimanjaro 82% of ice field has been lost since 1912 3.9

  28. Intergovernmental Panel on Climate Change (IPCC) Recognizing the problem of potential global climate change, the World Meteorological Organization (WMO) and the United Nations Environment Programme (UNEP) established the Intergovernmental Panel on Climate Change (IPCC) in 1988. It is open to all members of the UN and WMO. 3.9

  29. 3.9

  30. Kyoto Protocol - 1997 Conference • Intergovernmental Panel on Climate Change (IPCC) certified the scientific basis of the greenhouse effect. • Kyoto Protocol established goals to stabilize and reduce atmospheric greenhouse gases. • Emission targets set to reduce emissions of six greenhouse gases from 1990 levels. • (CO2, CH4, NO, HFC’s, PFC’s, and SF6) • Trading of emission credits allowed. 3.11

  31. The Kyoto Protocol, an international and legally binding agreement to reduce greenhouse gases emissions world wide, entered into force on 16 February 2005. Notable country who has not signed 3.11

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