Chapter 3 Chemistry in Context The Chemistry of Global Warming Chapter 3 Chemistry in Context Catatan: Diambil dari berbagai sumber Free Powerpoint Templates

Global Climate Change Mean annual global temperature,1960–2003

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

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.

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

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

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

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

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

Green House Effect 11

Molecular Vibrations: Energy Absorption by Greenhouse Gases

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 14-16 um region

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

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 ?

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

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

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

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

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

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

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

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

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

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

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

Molecular response to different types of radiation 3.4

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.

There are Seasonal Fluctuations in Carbon Dioxide Concentration

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

Carbon Dioxide Concentration has Increased since 1870

Ice core data and CO2 concentration

Carbon Dioxide Cycle

Fig.03.20

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

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 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

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

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

Chemistry behind Global Warming Avogadro's number is 6.0 x 1023. 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

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

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

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

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

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

3.9

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

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