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Chemistry 2210A/B
Kay Calvin

Chapter 1 Regions of electromagnetic spectrum; approximate wavelengths (especially for UV-A, B and C) UV C = 200-280 UV B = 280-320 UV A= 320-400 Visible = 400-700 IR= 700-1000+ Relationship between wavelength of light and the energy of its photons; how does this relate to the thermodynamics of chemical reactions 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 memorize 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 mid/upper stratosphere where NO is the catalyst, requires atomic O - M2 takes place in low stratosphere, 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 Interconversion of gas units 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 pla
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