Chapter 03 The Chemistry of Global Warming

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   The Chemistry of Global Warming

• • Mean annual global temperature,1960–2003

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  Global Climate Change

  

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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 role of human effects activities

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Difference

GLOBAL WARMING is the increase of the

CLIMATE CHANGE is a broader term that

  Earth’s average surface temperature due to a build-up of greenhouse gases in the atmosphere.

  refers to long-term changes in climate, including average temperature and precipitation.

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Effects of Global Warming

Increased Temperature Habitat Damage and Changes in Water Supply Rising Sea Level

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Venus has an average temperature of

450°C; It’s atmosphere contains 96 % CO

  2

Earth’s Energy Balance

  Shorter wavelengths are yellow; longer are red

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Sun’s Energy which Reaches Earth

• Ultraviolet (UV); 8 %
• Visible (vis); 39 %
• Infrared (IR); 53 %

   Page 9 Greenhouse Effect; Return of ~81 % of Re- radiated Energy Back Towards Earth _{Geoffrey Davies, Norton Gilbert,Rein V. Kirss, and in Context; by Thomas R} Chemistry; The Science

  Publishers, 2004, p335

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Molecular Vibrations: Energy

Absorption by Greenhouse Gases

  Major Greenhouse Gases:

Carbon Dioxide & Water

  CO absorption spectrum : strong peaks at 15 um and 4.26 ₂ µm (both of which are in the thermal IR but radiation from earth not very strong in 4-5 µm region)

   CO absorbs about ½ the radiation in the 14-16 um region ₂ Page 14

  

Page 15 Enhanced Greenhouse Effect Increases the average global temperature above the optimal amount due to an energy return greater than

  81%.

  

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  Gases Greenhouse Gases NOT Greenhouse Gases

• Carbon dioxide; CO
2<
• Nitrogen; N
2<
• Water; H O
2<
• Oxygen; O
2<
• CFC’s
• Argon; Ar O • Nitrous Oxide; N
2<
• Methane; CH
₄ why ?

   Page 17 Review: How to draw Lewis structures Draw Lewis Structures for:

  1. Determine the sum of valence electrons O CH _{2 4}

  2. Use a pair of electrons to form a bond SO C H _{2 2 4} between each pair of bonded atoms _2-

  SO CO ₄

  3. Arrange the remaining electrons to H SO _{2 4} satisfy octet rule (duet rule for H) ₂ ------------------------------- N _-

  4. Assign formal charges

• NO
₃ O _{3 - -}

  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!

  Representations of methane CH = molecular formula; does not express connectivity ₄ Structural formulas show how atoms are connected:

  Lewis structures This Lewis Space-filling Charge- structure is density show connectivity drawn in 3-D

  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 Four electron pairs as far from each other as possible indicates a tetrahedral arrangement.

  A tetrahedral shaped molecule has bond angles of 109.5 ^o .

  Valence Shell Electron Pair Repulsion Theory Consider methane (CH ₄ ), where the central carbon atom has 4 electron pairs around it:

  The legs and shaft of a music stand are like the bonds of a tetrahedral molecule.

  Valence Shell Electron Pair Repulsion Theory

  The central atom (O) in H O also has four ₂ The non- electron pairs around it, bonding electron pairs take up more space than bonding pairs, so the but unlike methane, two electron pairs are H-to-O-to-H bonding and two are non-bonding. bond angle is compressed. 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.

  We can use the VSEPR model to allow us to predict the shape of other molecules.

  Number of electron pairs Shape of molecule Bond around central atom angle _o

  4 electron pairs, all bonding: tetrahedral 109.5 CH , CF , CF Cl, CF Cl _{4 4 3 2 2} 4 electron pairs, three _o bonding, one non-bonding:

  Triangular pyramid about 107 NH , PCl _{3 3} 4 electron pairs, two _o bonding, two non-bonding: bent about 105

  H O, H S _{2 2} Other predictions can be made based on

  Now look at the central atom of CO ₂ : Two groups of four electrons each are associated with the central atom. The two groups of electrons will be 180 ^o from each other: the

  

CO ₂ molecule is linear. Molecular geometry and absorption of IR radiation Molecular vibrations in CO . Each spring represents a C=O ₂ 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

  The infrared spectrum for CO ₂ As IR _{radiation is absorbed, the} amount of _{radiation that makes it} through the _{sample is reduced}

  The infrared spectrum for CO ₂ Wavenumber (cm ^-1 ) = 10,000 wavelength (m) Molecular response to different types of radiation

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 CO ₂

• concentration

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

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There are

Seasonal

Fluctuations

in Carbon

  

Dioxide

Concentration

  Page 31 Over very long

periods of time; CO

₂ concentration has increased when average global temperature has increased.

   Page 32 Carbon Dioxide Concentration has Increased since 1870

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  Ice core data and CO ₂

concentration

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  Carbon Dioxide Cycle

  

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  Fig.03.20

  The carbon cycle A mole of atoms of any element has a

mass (in grams) equal to the atomic

mass of the element in amu.

  

Mole: SI definition: the number

equal to the number of carbon atoms in exactly 12 g of pure C-12.

  Avogadro’s number is 6.022 x 10 ²³ Atomic number Mass number

  23 Atomic number

  6.022 x 10 Mass number One mole of carbon has a mass of 12.01 grams; 1 mol C = 12.01 g If you have 36.03 g of carbon, how many moles is that? 1 mol C 36.03 g C x 12.01 g C = 3.0 mol C The carbon cycle

  moles molecules grams use molar mass use Avogadro’s number Keep these relationships in mind: Remember – the critical link between moles and grams of a substance is the molar mass. Chemistry behind Global Warming Calculate the number of molecules in 4.53 moles of ₂₄ carbon dioxide.

  2.73 x 10 Caffeine has the formula C H N O . How many _{8 10 4 2} molecules are in 10.0 g of pure caffeine? (The molar ₂₂

  3.1 x 10 mass of C H N O is 194 g/mol.) _{8 10 4 2} How many grams of CO are needed to be sure of _{2 2 4}

  1.3 x 10 g having exactly 3.0 x 10 mol of CO ? _{2 23} How many atoms are in 0.35 mol of CO ? 6.3 x 10 ₂ Chemistry behind Global Warming

  23 Avogadro's number is 6.0 x 10 . If we have a sample that contains one mole of carbon dioxide, how many atoms of oxygen are contained in that sample? ₂₃

  12 x 10 Deforestation contributes another 1-2 bmt/year CO ₂ emission sources from fossil fuel consumption

  Amplification of Greenhouse Effect: Global Warming:

  What we know 1. CO contributes to an elevated global temperature. ₂

  ₂ been increasing over the past century.

  ₂ consequence of human activity.

  What might be true:

  ₂ responsible for the temperature increase.

  2. The average global temperature will continue to rise as emissions of anthropogenic greenhouse gases increase.

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

  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. (CO , CH , NO, HFC’s, PFC’s, and SF )
_{2 4 6} •Trading of emission credits allowed. 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