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105bs10_w_sample1

105bs10_w_sample1 - bmmh{2010 Chemistry lOSbL First Letter...

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Unformatted text preview: bmmh {2010) Chemistry lOSbL First Letter of PLEASE PRINT YOUR NAME TN BLOCK LETTERS Fall 1995 , Last Name Exam #1 Name: Sept. 19, 1995 Professor Arieh Wamhel Soc. Sec. #: T.A.'s Name: Lab Day and Time: Please Sign Below: QUESTION MAXMUM SCORE GRADER POINTS -—-—— ——-_ “-— “—- ”—- —-a-—— I certify that I have observed all the rules of Academic Integn'ty while taking this exammafion. INSTRUCTIONS: 1. There are 5 problems on 7 pages in this exam. Please check to see that you have a complete exam. 2. Please show all of your work. Useful Physical Constants and Equations: Avogadro's number N = 6.022 x 1023 mol" Universal gas constant R = 0.08206 L atm K" mol" = 8.314 J K" mol“ Faraday's constant F = 96,485 C mol" Rate = k[A]"[B]"' t 1/2 lst order Rate = HA] In La]? ._._. kt _o_.:_9 = L _ 1 _ 2nd order Rate k [A f [A] [A]. __ ”All. 0th "d“ Rate = k ‘ [A]. - [A] = In 1%“- k = Ae—E./RT lnk=- %(JT-)+ lnA figure 14.1 [Hun-moo of the potential-energy profile for a boulder. The boulder must be moved over the energy barrier before it can come to rat in the lower-energy location. B. ‘3. (20 points) Please indicate if the statement is “True” or "False” for each of the following: (a) (b) (C) (d) (e) (D (s) (h) (i) (1') When Q < Kan the reaction goes backward. The difl‘erential rate law gives the dependence of concentration on temperature. Catalysts allow one to obtain the same rate constant but at lower temperature. Arrhenius' equation can be used to study the efl‘ect of catalysts on activation energy. Fritz Haber's discovery helped America in World War I. The halfer of first order reactions is independent of concentration. Biomolecular reactions lead to third order rate laws. Enzyme destabilize the charges of their transition states. The rate determining step is the fastest step in a reaction. * Pseudo first order reactions occur when all the reactants have the same concentration. True I l l l ’\I I\’\.! l 10 2. (20 points) The following data were measured for the reaction BF, (g) + NH3(g) —+ RENE, (g): (a) 0)) Experiment [BF3] (M) [NH3] (M) 1 0.250 0.250 2 0.250 0.125 3 0.200 0.100 4 0.350 0.100 5 0.175 0.100 What is the overall order for the reaction (show your work)? Rah: .vn (Wl, 0.713 Zng “0.12de 57733? mm What is the rate constant for the reaction? {la/‘9: k (0.254)).[0269 3 0.2130 MM H:0.213Q :- 3'L1fd.§S-’ 0.06.75 Initial Rate (M/S) 0.2130 0.1065 0.0682 0.1193 0.0596 MBFJ’MHQ‘” C“\ 3. (20 points) The reaction A —-) B is a first order reaction. The concentration of A changes with time according to the information below: time (sec) [A] 0.0 l .6 5.0 0.80 10.0 0.40 15 .0 0.20 20.0 0.10 (a) What is the rate constant for this reaction? Q“D*\-O]:ltwl {- 390 ’J’ {A} J2/V’ (ll 6‘\ , I (it) 3“” l" ””93“ (b) What is the half-life for this reaction? 0.6 {Hz :’ _9_3 3 5 sec K (c) If a reaction started with 0.2 M of A how long would it take to have only 0.05 M of A? 4. (20 points) Experimental values for the temperature dependence of the rate constant for the gas~phase reaction NO+O3—)N02+Oz are as follows: T (K) k (leol 5) 195 1.08 x 10’ 230 2.95 x 10’ 260 5.42 x 10° 298 12.0 x 109 369 35.5 x 109 (3) Determine the activation energy for this reaction. . .0 ‘ ‘.9 , ,E'e 19,) ‘ E ,l. - J2“(,.w.lo)+13fl(7-9ol0)— 73h; T‘)-*“7:[7-W‘Ho') -\'OQ§ ‘1 ‘7? (7 gold loL‘) Ea“. XZKCA‘R E ‘QkY/Mog (b) Determine the rate constant when the temperature reaches infinity (T = 00 ). it: h {Ea/M . 7"” ksfl WW}? .Q/n A \- Ea/ar Mtlotlot):—'2*_E.fi{ > gm l9§ Whifl‘l" A:,Q — ELM-)0 @ _ 5. (20 points) The reaction: exhibits the rate law: Rate = k[NO]2[Oz] 2N0 (g) + 02 (g) —+ 2N02(g) (3) Which of the following mechanisms is consistent with this rate law? 0) @. (iii) (iV) NO+02-)N01+O O+NO -)NO; NO + 01 2 N03 N03 + NO “) 2N0: 2N0 —+ N202 N202 + 02 ""> N204 N204 '—) 2N0: 2N0 2' N202 N202 —) N02 + O O + NO —‘) N02 slow fast both fast with equal rates slow slow fast fast may both fast with equal rates slow fast (b) Answer "true" or "false" on the following questions. (i) (ii) (iii) (M An elementary step of the form A + B + C --> ABC is very unlikely. Catalyst cannot change the temperature dependance of a reaction. The half-life of a second order reaction is independent of the concentration. Zero order reactions depend on the first power of the concentration. Arennius never saw snow in his life. True False 6. (zopoims) @1qu WWW its 0M Mama (a) For the gas-phase reaction H? + X2 = 21-Di, calculate the equilibrium constant at 501 K for the following equilibrium concentrations: [Hz] = 0.0025 M, [X2] = 0.0050 M, and [HX] = 0.0075 M. 2 mg; ml. (9.00;!) (0. 00fl> (b) What will be the direction of the above reaction when the concentrations are [Hz] =" 0.000] M, [X2] = 0.0001 M, [BX] = 1.0 M (ofcourse, the equilibrium constant is the same as in (3)). ‘ (/ 0)?‘ -_: /0‘? 63 7 K32 ram 3/0 74> 722/ [eff ...
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