Exam1_Spring06

Exam1_Spring06 - Ke‘i Chemistry 105 B Midterm 1 Professor...

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Unformatted text preview: Ke‘i Chemistry 105 B Midterm 1 Professor Bradforth Spring 2007 / 0 YOU MUST SHOW YOUR COMPLETE WORKING ON EACH OF PROBLEMS 6-9 TO RECEIVE FULL CREDIT. 0 STATE AND JUSTIFY ANY APPROXIMATIONS YOU MAKE. Useful Physical Constants and Equations TC = TK - 273.15 R = 8.314 J K‘1 mol'1 Zeroth Order reaction: [A] = [A]0 - kt half life t1/2 = [A]0/ (2 k) First Order reaction: In [A] =1n [A]0 - kt half life t1/2 = 0.693/k Second Order reaction: 1/ [A] = 1/[A]0 + kt half life t1/2 = 1 / (k [A]0) Arrhenius Equation: k = A exp(— EA/ RT) In(k) = In(A) — —%‘-( % j Multiple Choice questions (2 points each) : Question 1) A given reaction is found to be exothermic (gives off a significant amount of heat). What can be said about this reaction? (a) Since so much energy is given off the reaction will be very fast (b) The activation energy will be small (0) The reaction will be slow because energy is being given off (d) The potential energy of the products is greater than that of the reactants (e) None of the above Question 2) What are the units for the rate constant of a third order reaction? (a) mol L"1 s‘] (b) mol'1 L s“ (0) mol2 L'2 s" mol‘2 L2 s‘1 (e) s'1 Short Answer Question (no working required) Question 3) (3 points) Thiosulfate ion, SzOg2‘ is oxidized by iodine according to the reaction: zszofwaq) + Mag) 9 S4062‘(aq) + 21‘(aq> If in a given experiment, 0.0080 mol 82032' is being consumed in IL of solution every second, What is the rate of consumption of 12? Make sure to include units in your answer. 0.00 1+0 ML L" 3" Question 4) (6 points) The central idea of the collision model is that molecules must collide in order to react. Give two reasons why not all collisions of reactant molecules result in product formation. 11% uNtwA VWQKL WES {s s-mmr Wm M aware“ W3 EA Tm cow “~9- Mlm “PPM aw O‘LQF U “Ar EaNgmbiekvea/J'wfi ( S‘knc walw) Question 5) (7 points) The following reaction occurs inside an internal combustion engine: N02 + CO -) NO + C02 The following is a proposed mechanism: N02 + N02 9 N03 + NO (slow) N03 + CO '9 N02 + C02 (fast) (a) Which step is rate determining? What is the molecularity of that step? NmL—r— No7] ~—-> NO'S-f- NO Walsh) (4 ptS) bi MGM” (2'\ (b) Write down the overall rate law for the reaction based on the proposed mechanism. —- ’L (3pts) (71k: kLNTOI] Long Answer Questions. Full credit will require providing all your working. Question 6) (25 points) The hydrolysis of table sugar (sucrose) occurs by the following overall reaction: Sucrose, C12H22011 (s) + H20 (1) -) Glucose, C6H1206 (aq) + Fructose, C6H1206 (aq) A nutritional biochemist studies the kinetics of the process and obtains the following data: -———-—-——.—_—_—____—_______ Time (hours) [sucrose] (mol / L) ln[sucrose] 1/[sucrose] 0 0.501 -0.69 2.00 0.5 0.451 -0.80 2.22 1.00 0.404 -0.91 2.48 3.00 0.267 -1.32 3.75 (a) Using the attached graph paper, carefully make two plots of the experimental data. From these plots, show what the rate law is for the sucrose hydrolysis reaction. Explain your answer. a QL—Smxj VS_i‘\.r'\0; )3 CK Soul Jim‘jktlwi M imam] V3.H‘M ‘5‘ NDT— W ‘is Punter“er Ev) Womsmg) veg-3,644 (b) Using the graph, find the rate constant for the reaction. (15 pts) (10 pts) time/ hours Question 7) (20 points) Hemoglobin molecules in blood bind oxygen and carry it to cells, where it takes part in metabolism. The binding of oxygen Via Hemoglobin (aq) + 02 (g) 9 Hemoglobin - 02 (aq) is 1st order in dissolved oxygen and 1St order in hemoglobin with a rate constant of 4 X 107 L mol"1 s'l. (a) Write the differential rate law for the reaction. (3pts) W ~; lQ CHE-15°le (b) Calculate the initial rate at which oxygen will be bound to hemoglobin, if the concentrations of hemoglobin is 2 X 10'9 mol L'1 and that of oxygen is 5 X 10'5 mol L'l. mtg: (Lk we? Lmol" s“) (1 x m‘a Mal U‘) (s -< \BSMOL L“) (5 pts) ‘1 (c) Which reagent is in excess for these initial concentrations? Write the pseudo-first order differential rate law and calculate the pseudo-first order rate constant k' for these conditions. Oxwfim (5 m was: . (7pm) mk -. h' Cub] wk“ k': W321 R': (“x to? LmV‘s“) (5 X ‘0‘8 "‘“L Li“) ~\ 2 lo x \07’ s“ .: ‘2000 ‘l (d) How long would it take for half the hemoglobin to become oxygenated for these initial concentrations? e, __ (n1 0.683 __ B‘s->004; : 014 ms iii r ~—-—- : ‘ - z 4 (5 ms) h 2000 S 0" 003,715 Question 8) (15 points) ‘ In Houston (near sea level) water boils at 100.00C. In Cripple Creek, Colorado (near 9500 ft), it boils ’ at 900°C. If it takes 4.8 minutes to cook an egg in Cripple Creek and 4.5 minutes in Houston, what is Ea for this process? thf_»—€“ -‘_——_l.> h. ' fR— Tm T‘ (as; MM: M U“ ‘3‘“ 745 “Mm ‘°°“C ‘ (ruk (mag ’ " z, '/~tx 9‘ $73 3 3 0.0645 “£9 ' ama'x‘b SK“ Question 9) (20 points) Given the initial rate data below, we may consider the rate law for the reaction 2C102(aq) + 20H'(aq) 9 c103‘(aq) + C10; (aq) + H20 (1) The initial rate, -d[C102] / dt, was determined for the following concentrations of each of the reactants in 3 different experiments: [00210 [OH—10 Initial rate E ° t - - -1 .1 Xpenmen mol L 1 mol L 1 mol L S 1 1 x 10‘3 0.1 5.75 x10—2 2 1.73 x 10'3 0.1 1.7 x10-1 3 1 x 10‘3 0.25 144 x 10'1 (a) What is the order of this reaction with respect to C102? NH“ 593 Wt koflmdaxn raki— §f4§xm~2 RCIXID‘EB'KCDJY‘ W2 - K lb“ C/_73xlo';)x(0“)n (5pm) 29 o~ 25% :- (0.378] Wis Wma C4131 (5 PtS) (5 ptS) - (5 pig) Question 9 continued) (b) Determine the order of the reaction with respect to OH: (c) Write down the overall differential rate law for the reaction. Wk : h CCLDq—llEOH’l ((1) Calculate the value of the rate constant, giving appropriate units. Dix/£5 \ml 2- 373 x nil mok LU“ :_— h (\xso~3mn’LL“) (a; mol L‘) [0 K) S17S‘x io‘l mow“: “‘ : 5752*.2125“ : ~A____‘_ (\x \0‘3 wk L“) ED. 1 Mo\. L“) ...
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Exam1_Spring06 - Ke‘i Chemistry 105 B Midterm 1 Professor...

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