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final exam chemistry 2210A review

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Chemistry 2210A/B
Kay Calvin

Chapter 1 Absorption of light by molecules; what does a spectrum tell you? - molecules and bonds absorb at different frequencies of light - Wavelengths shorter than 120 absorbed by O2 and N2 - O2 above stratosphere absorbs most UV light from 120-220 (C) - Some light from 220-240 (all C) - O3 absorbs light in 220-290 range (all of C, very little B) - Shorter the wavelength, more absorption  will not reach Earth Ozone creation and destruction in the stratosphere; the Chapman Cycle (don’t memo rize equations; just what is happening?) - First reaction: O2  2O (absorb UV-C, shortest wavelength, highest energy) o Above stratosphere ! filters most UVC before reach strato, mostly O - Second reaction: O + O2  O3 + heat o In stratosphere, oxygen mainly molecular - Third: O3 absorbs UVA  O + O2 - Fourth: O3 + O  2O2 (small extent, high Ea) - Cycle is naturally occurring during daylight hours, and occurs in stratosphere Catalytic ozone destruction; what are the catalysts? How are the two mechanisms different? Mechanism 1: - O3 + X  XO + O2 - XO + O  O2 + X - Overall: O3 + O  2O2 Mechanism 2: requires atomic O - X + O3  XO + O2 - X’ + O3  X’O + O2 - Either X or X’ must be Cl; other can be Cl or Br - XO + X’O  X’OOX  X + X’ + O2 - Overall: 2O3  3O2 Differences: - M1 takes place in upper stratosphere where NO is the catalyst, requires atomic O - M2 takes place in low stratosphere, also uses two different species for each step Chapter 2 How is the Antarctic ozone hole created? Activation of chlorine, describe process, not reproduce all the reactions. - hole created when O3 conc in lower strato is 0 - winter conditions convert inactive Cl (HCl,ClONO2) to active (Cl, ClO) - high amounts of Cl destroy large amounts of O3 - conversion occurs at surface of particles formed from water H2SO4,HNO3 o become solid bc of cold; form polar stratospheric clouds - because dark, no UVC/B to convert O2 + O  O3, no ozone, no heating Substances that contribute to ozone depletion; CFCs and replacements - Cl and Br = culprits (no sink) - CFCs (contain Chlorine + Fluorine + Carbon), no sink, float to stratosphere o No sink bc to break CF bond takes much more energy than to form OF, endothermic, reaction occurs slowly - Chlorine containing substances o Carbon tetrachloride, CCl4 o Methylchloroform CH3-CCl3 - CFC replacements: all replacements contain CH bonds, resulting in removal o Reactions occur in troposphere, hence never make it to stratosphere, CO2 produced; CO2 does not break down as quickly o HCFCs temp replacements; no long term implications o Ultimate replacements will contain no Cl o HFCs main compound now being used - Greatest destruction to least: Anything with Cl will destroy ozone (more Cl = more destruction); followed by HCFC because CH = sink, but still contains Cl; followed by HFC which has no Cl Chapter 3 Importance of the OH free radical in atmospheric reactions - oxidation initiated by OH free radical bc of free unpaired electron  very reactive - source of OH is natural ozone o O3 + UVB  O + O2 o O + H2O  2OH - Lifetime very short, amounts small, but very reactive hence good tropospheric vacuum cleaner Photochemical Smog is mainly due to NO; components, how is it formed (in general); different maximum amounts of components at different times of day - Photochemical smog = ozone in the wrong place! Ground layer sometimes? - Reaction: o NO2 + UV-A  NO + O o O + O2 (found in stratosphere)  O3 o O3 + NO  O2 + NO2 - NO comes from auto emissions; morning when everyone commuting to work is when NO rates are highest, then NO2/O3, drops at night because there is no light to keep process going (dissociation by UV-A) - NO (primary product) + O2 + sunlight  O3 + HNO3 (secondary products) VOC limited vs NOx limited reactions; effect on ozone formation? - usually VOCs in excess , reduce one in excess = little effect - if NOx limiting reagent, need to reduce it - ex. Point A, lots of VOC (1.2ppm) limited NOx (0.04ppm), VOC in excess o if we reduce VOC from 1.2-0.8, there is no change in O3 o if we reduce NOx from 0.04 to 0.01 then O3 has reduced - ex. Point A, lots of NOx (0.20ppm), minimal VOC (0.5), NOx in excess o if we reduce NOx from 0.20 – 0.12, O3 has actually increased o if we reduce VOC from 0.5 – 0.3, O3 decreases Solubility of gases in water (use of Henry’s Law and constant); calculations - solubility of gas increases with increasing pressure - the more gas you have, the more will dissolve - KH(constant) = C (concentration) / Pgas (pressure) Chapter 4 Health problems related to soot and smog - can cause death in person with respiratory problems - SO2 smog contributes to acidic pollution o Burning of brown coal contains 15% S which is a main cause o Smog is reducing in nature due to presence of SO2 (which is oxidized) - Photochemical smog much more significant o Oxidizing in nature o Ozone is dangerous, attack C=C biological tissues o NO2 also implicates death from circulatory diseases Indoor air pollution….what compounds contribute? - Formaldehyde; H2C=O o Emission from cigarette smoke, rate of emission increases with temperature/humidity, declines as material ages (half life?) o Carcinogen! o Most important VOC in sick building syndrome  people that work in building and experience symptoms but no known disease  Chest pain, bronchitis, eyes watering, dizziness, fatigue - Benzene and Hydrocarbons; C6H6; volatile liquid hydrocarbon o Component of gasoline, used in paints/ink o Carcinogen! Never breaks down in body o Replaced by toluene (also carcinogen) - NO2 o Formed form thermal NO, from appliances that use gas as fuel  N burning in O at high temp, appliances, natural gas, propane o Soluble in biological tissue, absorbed in body, is an oxidant - CO o CO is odourless/colourless o Caused by incomplete combustion of carbon fuels, also found in cigarette smoke o Not enough oxygen, it is the limiting reagent o Combines with hemoglobin in blood, interferes with oxygen transport  TOXIC - Environmental tobacco smoke: second hand o Consists of gases (CO, H2C=O, NOx) and particles (tar) o May cause irritation of eyes, aggravate asthama/angina o Carcinogen, extremely harmful for infants (sudden infant death syndrome) - Asbestos o Fibrous, silicate material o Used in insulation, fireproofing o Carcinogen! Causing mesothelioma (cancer of chest cavity/abdomen) o Cigarette smoke and asbestos act synergistically !! o Should not be removed if will aggravate particles and cause them to float in air, if stable/contained it will do no harm, leave it Chapter 5 Wavelength regions of incoming radiation (from the sun) and outgoing (from the Ear th). - emission wavelength = temperature based - 2897/T (in K) = wavelength peak (in nm) - from the sun = wavelengths UV, visible and IR ....peak in visible (400-750nm) - from the earth = wavelengths IR (energy absorbed from sun, less emitted hence IR) - 50% of sun radiation absorbed (20% IR absorbed by water, CO2; UV absorbed by ozone and O2) Albedo; what is it and how does it vary with surface? - Ability to reflect light - 30% reflected back into space (70% stay absorbed) = albedo; clouds, snow, ice all reflect light - water/soil better at absorbing - rate of emission of light increases as temperature is raised Greenhouse Effect and Enhanced Greenhouse Effect; how are they different? Describ e the processes in general terms. Greenhouse Effect: greenhouse gases (such as CO2, water vapour) capture IR radiation and either re-emits it as IR, or after absorbing emits it as heat. Random and warms air near surface...natural billions of years Enhanced Greenhouse Effect: not so natural, increasing concentration of trace gases in air that absorb IR light , increase surface temperature well beyond 15 degrees What are the major greenhouse gases? What is feedback? What is the atmospheric window and what is its significance? 1. CO2 : absorbs at 2.46nm (asymmetrical stretch) + 15nm (bend) In spring/summer because of growth of vegetation, CO2 extracted from air CO2 + H2O  O2 + polymeric CH2O Fossil fuels from home heating added in winter Forests cleared for wood or land, wood burned = CO2 2. Water Vapour: 2.7 (asymmetrical) + 6.3 bending absorbs through bending (less IR light than CO2 per molecule) Increase in temperature = more water vapour = more warming POSITIVE FEEDBACK 3. CH4: bending vibrations (7.7nm), lifetime less than 10 years; 90% of CH4 removed by OH sink; CH4 + OH*  CH3* + H20 (first reaction = CH4  CH20 CO CO2) *** per molecule 20x more efficient at absorbing IR Methane trapped in ice, 2CH20  CH4 + CO2 4. N2O (nitrous oxide) : absorbs IR at 8.6 (bending) and 7.8 (stretching); no sink, last 120 years; produced by nitrification and denitrification 5. CFCs – C-F: 9um  in window! Heating from IR counteracts cooling happening in stratosphere when break down ozone; long lifetime 6. Tropospheric ozone: short lived, absorbs in window, photochemical smog 7. SF6 (sulfur hexafluoride): long lived, good absorber Feedback: Positive: event produces a result that further amplifies the result Negative: system whose output reduces subsequent output Atmospheric Window: IR light from 8-13um escapes atmosphere efficiently , gases that absorb in this region = further enhance greenhouse effect Amount of light absorbed by particles is linearly proportional to conc bc logarithmic but if C=0 then linear (directly proportional) Chapter 6 What are the main energy sources? (Figure 6‐3) - Fossil Fuels o liquids (biofuels) ex. Crude oil o coal o natural ags - renewables - nuclear Petroleum refining; describe process of fractional distillation - separating into fractions so have equal number of C thus similar boiling points - fractioning tower, cooler at top, hot at bottom C17 + = good lubricants, not good for car C3-12 = gasoline! 20% of crude oil C12-16 = diesel! Home heating oil C16-18 = diesel! Industrial heating oil C1-12: uncondensed vapour; C5-12 MAIN, higher than 12 = won’t work (boils at too high temp) Compounds in gasoline; octane rating and fuel additives - CH ; mainly C7-C8; unbranched alkanes andcycloalkanes - Highly branched alkanes such as octane isomer (100) prevent knocking - Ability of gasoline to start engine without knocking – octane number - Distillation produces gasoline with octane 50, cars need 87 - So add: tetramethylead Pb(CH3)4 and tetraethyllead ....environmental concern - MMT controversial for health reasons - BTX (benzene, toluene, xylene)....more photochemical smog ; benzene carcinogen? no catalytic converter? - BTEX (trimethylated benzene and ethylbenzene) - MTBE Chapter 7 Ethanol; uses and production (both from starch and from cellulose) - C2H5OH = ethanol - Easily blend with gasoline ; E10 used in NA (10% ethanol in gasoline) - Helpful bc of low vapour pressure - Too high vapour pressure = evaporation with VOC in air, lower VP stops this - Peak in vapour pressure is when 90%gasoline, 10% alcohol, good for cold starts - 1.25vol ethanol per 1vol gasoline Production from starch: fermentation of carbohydrates - we get our carbs (glucose) from starch - simple starches found in sugar beets, sugarcane, corn etc - C6H12O6 yeast 2CO2 + 2C2H5OH (fuel; starch into glucose, glucose into alcohol by yeast fermentation) - Need water for fermentation process; solution needs to be dilute (yeast will die in too much alcohol); remove water by distillation (huge energy) 95% ethanol, 5% water each time Production from cellulose: fermentation of ligin - cellulose and hemicellulose from plants - second generation biofuel, not produced from edible food crops instead corn stalks, or woody plants; more sustained, more advantages - cellulose into sugar by enzyme hydrolysis then forms ethanol o no natural enzyme, genetic engineering produce enzymes that will ferment both C5 and C6 sugars - combustion of ligin used to fuel distillation process (removal of water) Balances between energy gained from biofuels and energy used to produce them - Biofuels are fuels made from plant materials - Energy gained bc renewable source, carbon based, oxygen - Energy lost bc of conversion of biomass to biofuel, payback period and clearing land - Causes 86% (vs higher % in gasoline) of enhanced greenhouse effect - Requires 2/3 amount of fossil fuel that would be required to generate the same energy in gasoline - Soybean derived biodiesel generates 90% more energy then used to produce vs 25% for corn based ethanol; CO2 emissions reduced by 40% Biodiesel; uses and production - B numbering system, B20 most common, B2, B5, B7 also popular Plant Oils (straight vegetable oils SVO) - plant oils burn well, lots of heat and smoke, but contain 50-60C - because so viscous, need to preheat
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