1. Chapter 3 Chemistry in Context
The Chemistry of Global Warming
Chapter 3 Chemistry in Context
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2. Global Climate Change
Mean annual global temperature,1960–2003

4. Definition
the accelerated warming of earth's atmosphere that is believed to result from a buildup of one or more greenhouse gases (primarily carbon dioxide, methane, and nitrous oxide) due to human activities =
the increase in average global temperatures
the scientific evidences
What are ?
the role of chemistry in understanding
the effects
role of human activities

5. Difference GLOBAL WARMING
is the increase of the Earth’s average surface temperature due to a build-up of greenhouse gases in the atmosphere.
CLIMATE CHANGE
is a broader term that refers to long-term changes in climate, including average temperature and precipitation.

6. Effects of Global Warming
Rising Sea Level
Increased Temperature
Habitat Damage and
Species Affected
Changes in Water Supply

7. Venus has an average temperature of 450°C; It’s atmosphere contains 96 % CO2

8. Earth’s Energy Balance
The Average annual temperature
of Earth is 15°C or 59°F
Earth’s Energy Balance
Shorter wavelengths are yellow; longer are red

9. Sun’s Energy which Reaches Earth
Ultraviolet (UV); 8 %
Visible (vis); 39 %
Infrared (IR); 53 %

10. Greenhouse Effect; Return of ~81 % of Re-radiated Energy Back Towards Earth
Chemistry; The Science
in Context; by Thomas R
Gilbert,Rein V. Kirss, and
Geoffrey Davies, Norton
Publishers, 2004, p335

11. Green House Effect 11

13. Molecular Vibrations: Energy Absorption by Greenhouse Gases

14. Major Greenhouse Gases: Carbon Dioxide & Water
CO2 absorption spectrum : strong peaks at 15 um and 4.26 µm (both of which are in the thermal IR but radiation from earth not very strong in 4-5 µm region)
CO2 absorbs about ½ the radiation in the um region

16. Enhanced Greenhouse Effect
Increases the average global temperature above the optimal amount due to an energy return greater than 81%.

17. Gases why ? Greenhouse Gases Carbon dioxide; CO2 Water; H2O CFC’s
Nitrous Oxide; N2O
Methane; CH4
NOT Greenhouse Gases
Nitrogen; N2
Oxygen; O2
Argon; Ar
why ?

18. Review: How to draw Lewis structures
Draw Lewis Structures for:
O2 CH4
SO2 C2H4
SO42- CO
H2SO4 N 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

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

20. 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

21. 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

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

23. 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

24. We can use the VSEPR model to allow us to predict the shape of other molecules.
Number of electron pairs around central atom
Shape of molecule
Bond angle
4 electron pairs, all bonding: CH4, CF4, CF3Cl, CF2Cl2
tetrahedral
109.5o
4 electron pairs, three bonding, one non-bonding:
NH3, PCl3
Triangular pyramid
about 107o
4 electron pairs, two bonding, two non-bonding:
H2O, H2S
bent
about 105o
Other predictions can be made based on other electron pair arrangements .
3.3

25. 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

26. 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

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

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

29. Molecular response to different types of radiation
3.4

30. How to study global warming
Ice core data
Ice Core data is used to infer temperature from deuterium content and estimate CO2 concentrations for air bubbles
Athmospheric CO2 concentration
Over very long periods of time; CO2 concentration has increased when average global temperature has increased.

31. There are Seasonal Fluctuations in Carbon Dioxide Concentration

32. Over very long periods of time; CO2 concentration has increased when average global temperature has increased.

33. Carbon Dioxide Concentration has Increased since 1870

34. Ice core data and CO2 concentration

35. Carbon Dioxide Cycle

38. Fig.03.20

39. 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

40. One mole of carbon has a mass of 12.01 grams; 1 mol C = 12.01 g
Atomic number
6.022 x 1023
One mole of carbon has a mass of grams;
1 mol C = g
Mass number
If you have 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

41. 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.
3.7

42. Chemistry behind Global Warming
Calculate the number of molecules in 4.53 moles of carbon dioxide.
2.73 x 10 24
Caffeine has the formula C8H10N4O2. How many molecules are in 10.0 g of pure caffeine? (The molar mass of C8H10N4O2 is 194 g/mol.)
3.1 x 1022
How many grams of CO2 are needed to be sure of having exactly 3.0 x 102 mol of CO2?
1.3 x 104 g
How many atoms are in 0.35 mol of CO2?
6.3 x 1023

43. Chemistry behind Global Warming
Avogadro's number is 6.0 x If we have a sample that contains one mole of carbon dioxide, how many atoms of oxygen are contained in that sample?
12 x 1023

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

45. 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

46. 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

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

48. 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 It is open to all members of the UN and WMO.
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49. 3.9

50. 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

51. 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
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