Chemistry in Context: Chapter 3:The Chemistry of Global Warming Practice Problems: All Ch. 3 problems with the blue codes or answers on Page 521. 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
History of Global Warming-2 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 ( 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. Fig. 3.2 on Page 101 Fig. 3.2 Page 101
Figure 3.4 page 103 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 3.5 page 104 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.
Figure 3.6 Page 105 Lewis Structures and Molecular Shapes 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 (decreasing repulsion ) Methane (CH 4 ) vs. CFC-11 Figure 3.9 Page 109 Tetrahedral 4 bp & 0 lp Non-polar CH4 Slightly polar CFC-11 Fig. 3.8 Pg. 108 Ammonia (NH 3 ) -Triangular pyramid Lone pair on N pushes 3 bonding pairs, N-H, downward.
Figure 3.10 Pg. 109 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) Fig. 3.11 Pg. 110 Fig. 3.12 Pg. 111 CO 2 Greenhouse Gases linear CH 4 tetrahedron H 2 O bent CFCs tetrahedron NH 3 triangular pyramid 3.9 Your Turn page 110 3.10 Your Turn page 111 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.
Figure 3.13 Page 112 Fig. 3.14 Figure 3.14 page 113: 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. 3.15 Page 113 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. (Fig. 3.16 Pg. 114)
Carbon Cycle Figure 3.13 page 115 Pg. 116 CO 2 output = CO 2 input? Fossil Fuel contribution Pg. 117 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
Mass Number CO 2 Emission sources in US Figure 3.17, Page 117 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! Avogadro s Number Avogadro s Number = 6.02 x 10 23 1 mole = 6.02 x 10 23 atoms, molecules, or charged particles Mole is a convenient unit for counting very small particles contained in gram quantities of chemical substances. Atomic Mass of Elements 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 can be measured by units of atomic mass unit (amu) or grams per mole. 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: Mass of an Atom What is the mass of 1 oxygen atom expressed in grams? Atomic mass is 15.9994 grams of oxygen per mole of oxygen atoms Since 1 mole contains 6.02 x 10 23 oxygen atoms, atomic mass divided by Avogadro Number gives the mass of one oxygen atom. Example Continued 15.9994 g oxygen = 6.02 x 10 23 oxygen atoms 2.66 x 10-23 g oxygen oxygen atom Practice 3.19 Your Turn on Page 121 for the mass of a nitrogen atom and five trillion atoms. Chemical Reaction & Moles C + O 2 CO 2 The numbers of atoms and molecules involved in a reaction are proportional to the number of moles of the substances expressed in a balanced chemical equation (i.e. stoichiometric coefficients). Page 122
Molar Mass The mass of one Avogadro s number (i.e. 1 mole) of molecular formula units of a chemical compound expressed in grams. Molar mass is calculated by summing the atomic masses according to the molecular formula. Example: Molar Mass Calculation What is the molar mass of NH 3? Find atomic mass for 1 mole of each atom in the molecule: N=14.01 g; H=1.008 g For NH 3, add the mass of nitrogen to that of hydrogen! (3 x 1.008) g + 14.01 g = 17.034 g Molar mass of NH 3 = 17.034 g per mole of NH 3 Mass of one NH 3 molecule = 17.034 amu Methane CH 4 in natural gas is an important greenhouse gas. CH 4 is produced in cattle farming, rice growing, petroleum refining, termite mounds, and landfills. 30 times more efficient than CO 2 in trapping IR But there is less CH 4 (~1.8 ppm) than CO 2 (~370 ppm) in the atmosphere! Table 3.4 on Page 125
Figure 3.19 Page 126 Methane in Ice Deposit from Ocean Floor Nitrous oxide N 2 O or laughing gas is used as inhaled dental/medical anesthetic. Anthropogenic sources of N 2 O are synthesized fertilizers and burning of biomass. Agriculture exacerbates N 2 O problem. Also plays a role in O 3 depletion, which has a cooling effect in the stratosphere Table 3.5 on Page 126 Greenhouse factor is a value that represents the relative contribution of a molecule of a substance to global warming. Climate Modeling Many factors are involved; examples include solar radiation, wind patterns, cloud cover, volcanic activity, dust and soot, ocean currents, and living things. Intertwined factors make it difficult to study and the effect of CO 2 independently. Computers are used to project what if scenarios. IPCC (Intergovernmental Panel of Climate Change) reaffirms the role of CO 2 in warming.
Figure 3.21 Page 129 Table 3.7 Page 131 Figure 3.22 Page 130 Fig. 3.23 Page 132
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. Fig. 3.24 Pg. 134 Blue - Red - 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 Fig. 3.20 Fig. 3.25
Fig. 3.26 Pg. 140 Debate Topic: Stratospheric Ozone Depletion Vs. Global Warming Based on what you have learned regarding global warming and ozone depletion, determine which is a more serious environmental threat. Refer to Table 3.8 Defend your position with facts