Final Exam Sp07

Final Exam Sp07 - CHEM173 Final Exam Spring 2007 1. a) b)...

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CHEM173 Final Exam Name_______________________ Spring 2007 UCSD ID Number______________________ 1. Stratospheric Ozone (20 pts: 5, 5, 5, 5) a) What is the name of the set of reactions that control O 3 formation and destruction in the stratosphere? b) Write the four reactions named in part (a). c) What three factors are needed to calculate the rate constants for the photolysis reactions in part (b)? Which of these factors varies most with altitude? Why? d) What is the typical concentration of ozone in the ozone layer? a) The Chapman cycle describes the four steps by which O 2 is photolyzed to produce O atoms and O 3 , which can then be photolyzed to recover O 2 . b) O 2 +h ν O+O O+O 2 +M O 3 +M O 3 +h ν O 2 +O O+O 3 O 2 +O 2 c) Photolysis rate constants are calculated from quantum yield, absorption cross-section, and photon flux. Photon flux varies most with altitude because light absorbed higher in the atmosphere does not penetrate to lower levels of the atmosphere, e.g. UV light is higher above the ozone layer. d) Ozone has a concentration of up to 5-10 ppmv in the ozone layer.
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CHEM173 Final Exam Name_______________________ Spring 2007 UCSD ID Number______________________ 2. Ozone Hole (40 pts: 5, 15, 5, 5, 10) a) What is the name for the depletion of the stratospheric ozone layer at the Arctic and Antarctic poles? b) The following questions refer to the depletion of stratospheric ozone in part (a). i) What meteorological feature of the polar regions is needed to transport Cl species downward from above 25km? ii) What type of clouds form when stratospheric ice freezes below 80C? iii) What two species release Cl2 by reactions on stratospheric ice particles? iv) What reaction releases Cl from Cl2 in springtime? v) What role do Cl species play when they are in the ozone layer? c) What is the role of chlorofluorocarbons in the depletion of stratospheric ozone in part (a)? d) Write the mechanism responsible for destruction of ozone by NO. e) State the net reaction for the cycle below. What role does it play in the ozone hole? ClO + ClO + M k 1 ClO ( ) 2 + M ClO ( ) 2 + h ν j 2 Cl + ClOO ClOO + M k 3 Cl + O 2 + M 2Cl + 2O 3 k 4 2ClO + 2O 2 Write expressions for the rates of destruction of Cl, ClOO, and (ClO) 2 in terms of the concentrations of Cl, ClOO, (ClO) 2 , ClO, O 3 , and M and the constants k 1 , j 2 , k 3 , and k 4 . a) The ozone hole describes the depletion of the stratospheric ozone layer at the Arctic and Antarctic poles. b-i) Polar vortex transports HCl, ClO and ClONO 2 produced by photolysis at 25km. b-ii) Stratospheric ice (<-80ºC) forms PSCs. b-iii) HCl and ClONO 2 make Cl 2 on PSC particles. b-iv)
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Final Exam Sp07 - CHEM173 Final Exam Spring 2007 1. a) b)...

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