midterm2 - Chemistry 173/273 Midterm #2 26 May 2009 Prof....

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1 Chemistry 173/273 Midterm #2 26 May 2009 Prof. K. Prather NAME:____________________ STUDENT ID:___________________ SHOW ALL WORK ON EXAM OR ZERO CREDIT WILL BE GIVEN IF NOT ENOUGH INFORMATION IS GIVEN For most of these questions, as indicated by the length of the space, only brief answers are required. If you know the answer, fill it in. If you don’t, move on to the next question. Go back to the questions for which you are less sure of the answers at the very end of the time period for the exam. 1. ______________ /14 2. ______________ /15 3. ______________ /15 4. ______________ /15 5. ______________ /66 TOTAL MIDTERM ______________ /125
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2 1. 14 points total, 7 points each part Henry’s constant for the solvation of NH 3 in rainwater is H NH3 = 62 M/atm, and the equilibrium constant for the following reaction: NH 3 H 2 O(aq) NH 4 + (aq) + OH - (aq) is K 2 = 1.8×10 -5 M. (a) What is the pseudo-Henry’s constant H * as a function of H NH3 , K 2 , and [OH - ]? (b) Assume a mixing ratio NH 3 (g) of 33 ppt at STP, and assume a droplet with pH = 7.6 in equilibrium with the atmosphere, what is the concentration of [NH 4 + ] in the droplet?
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2. 15 points, 4 points each (a) and (b), 7 points (c) The Leighton relationship for [NO 2 ], [NO], and [O 3 ] can be modified to include [RO 2 ] for the following scheme of reactions: NO 2 + h ν (<420 nm) Æ NO + O( 3 P) Rate constant = k 1 O( 3 P) + O 2 Æ O 3 Rate constant = k 2 O 3 + NO Æ NO 2 + O 2 Rate constant = k 3 RO 2 + NO Æ RO + NO 2 Rate constant = k 4 (a) Why does this new relation improve accuracy in atmospheric chemical calculations? (b) Here k 1 is considered a rate constant, but has a distinct dependence that rate constants k 2 -k 4 lack, what does this tell us about the diurnal variability of the Leighton relationship? (c)
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This note was uploaded on 10/28/2010 for the course CHEM 173 taught by Professor Dr.dancziczo during the Spring '10 term at UC Riverside.

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midterm2 - Chemistry 173/273 Midterm #2 26 May 2009 Prof....

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