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KEYEXAMII - CHEMISTRY 142 EXAM II April 5 2007 Section 004...

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Unformatted text preview: CHEMISTRY 142 EXAM II April 5, 2007 Section 004 Name: KEN Signature: (your signature above is your honor pledge) General Exam Information: 1. Pages of useful information are attached to the end of the exam. TheSe pages may be removed. 2. Remember to u5e Significant Figures. Points will be deducted if answers lack proper significant figures. 3. Show your work as possible as neatly as possible. I can only give partial credit for work I can follow and read. 4. Read questions completely and answer the question that was asked. —_ —_ _— — — _ Part IV (36) Total (93) Part I: Fill in the Blank. Fill in the blank with the term that best describes the phrase (3 pts each). 1. 'l’i‘CmS I‘l‘l on glak. is a point during a chemical reaction when what “(limited Gamma exists is neither a product nor reactant but a ' unstable species with partial bonds that cannot be isolated. . ' . Um aid 2. KC— 6‘ E lf‘llh‘m is a nxulmber equal to a particular ratio of equilibrium concentrations of product and ____;=————- _—u§'_‘ reactant at a particular temperature 3. BYQRSlfiClr L000“. is an acid—base definition that describes a baSe as any species that accepts an H" 4. Mflmhi is a term used to describe an acid with more than one ionizable proton I 5. Comm; SQ“ ' is the name of the phenomenon/ principle that describes how buffers work Part II Multiple Choice. Select the correct answer for each of the following questions. (4 pts each) 1. The reaction of nitric oxide to form dinitrogen oxide and nitrogen dioxide has a negative AHO value. 3NO(9) «1 N20(9) + N02(g) What effect will be seen if the temperature of the system at equilibrium is raised by 25°C? a. The partial pressure of N02 will increase. b. The partial pressure of NO will decrease. C? The partial pressure of NO will increaSe. . The partial pressures of NO and N20 will increase. e. All three partial pressures will increase. 2. Calcium oxide, CaO, will react with carbon dioxide, CO; to form calcium carbonate, CaCOa. Which species, it any, acts as a Lewis acid in the reaction? a. Ca2+ e. None of the species acts as a Lewis acid in this reaction. 3. The reaction quotient, Qc. for a reaction has a value of 75 and K; has a value of 195. Which of the following statements is accurate? a. The reaction must proceed to the left to establish equilibrium. 6) The reaction must proceed to the right to establish equilibrium. c. The concentrations of the products will be much smaller than the concentrations of the reactants when the system is at equilibrium. d. The concentrations of the products will be about the same as the concentrations of the reactants when the system is at equilibrium. e. None of these statements is accurate. I 4. The reaction system 652(9) + 4Hz(g) == CH4(9) + 2H25(g) is at equilibrium. Which of the following statements describes the behavior of the system if the partial pressure of hydrogen is doubled? a. As equilibrium is reestablished, the partial pressure of carbon disulfide increaSes. b. As equilibrium is reestablished, the partial pressure of methane, CH4, decreases. © As equilibrium is reestablished, the partial pressure of hydrogen decreases. d. As equilibrium is reestablished, the partial pressure of hydrogen sulfide decreases. e. As equilibrium is reestablished, all the partial pressures will decreaSe. 5. Which one of the following pairs is not a conjugate acid—base pair? a. HzO/OH' b. H202/l‘l02’ c. OH‘/OZ‘ d. HzPO4’/HPO4Z" HCi/i—r 6. Ammonium chloride is used as an electrolyte in dry cells. Which of the following statements about a 0.10 M solution of NH4Cl, is correct? a. The solution is weakly basic. b. The solution is strongly basic. c. The solution Is neutral. @) The solution is acidic. e The values for K, and Kb for the species in solution must be known before a prediction can be made. 7. Which one of the following substances will give an aqueous solution of pH closest to 7.0? a. NH3 b. NaCIO c. NH4Cl .KNOs Part III. Short Answer 1. The reaction of A(g)+ 3(9)» A391 is endothermic and proceeds through one transition state. On the empty reaction energy diagram below, sketch the reaction profile. In addition CLEARLY label bath aXes starting materials (Agni- 3(9)) products (AB{9)) the transition state and Eaf or the for the forward reaction ( 8 pts). /.+mfi§\\"\°'\ fink Poi; Use the reaction and diagram below to answer the next two questions. For the reaction of Ag) + 32(9) 4=FAB© 4- 3(9) AH < 0. The following scenes depict different reaction mixtures (A = Solid ball, B: hollow ball). . i 1 to“; 2 gm. 3 KC}?— 2. If Kc = 2 at the temperature of the reaction, which scene above (1, 2, or 3) represents the mixture at equilibrium? (3 pts) Kg: 2 “its“: 3) 3. For the reaction at equilibrium, how will a rise in temperature effect [32] (3 pts)? Wm P); teem (an is Within-it Part IV. Problem Solving. Show your work to receive full credit and place your final answer in the box provided. A- __ _ ____ ___,,_ __ ._ ___ 1. The reaction CH3NC(9) -—> CH3€N(9) is first—order with respect to methyl isocyanide, CHaNC. If it takes 10.3 minutes for exactly one quarter of the initial amount of methyl isocyanide to react, what is the rate constant? (6 pts) t3 \t) .5 "(m m1, : H; [Al log—'3- "' \Lk [EA-l Y, O (>qu Mm" Obi-“Iain: 2. What is the mass-action expression, Q, for the following chemical reaction? (6 pts) 4H30’(aq) + ZCI'(aq) + Mn02(s) 2' Mn2*(aq) + 6H20U) + Cl2(_q) 3. For the reaction A0) + 3(9) + Co) —» Dig) the following data were obtained at constant temperature (concentrations given in mol/L): Ex eri ent# Initial A Initial B Initial C Initial Rate moi/L-sec 1 0.0500 0.0500 0.0100 6.25 x 10-3 2 0.1000 0.0500 0.0100 1.25 x 10'2 3 0.1000 0.1000 0.0100) 5.00 x 10-2 4 0.0500 0.0500 0.0200 6.25 x 10'3 0) Write the rate law and b) calculate k (using data from experiment 1). E: ”L ms) b) wk = ms 20 35 Expiéé doohkfisj roll! flow)". 501:8] Ext" \ 75 clam [t3 “0 0"“ 9' )3 L‘ t C 4. A chemical engineer is studying the oxidation of 502 during sulfuric acid production and she determines that the Kc = 1.70 x 108 at 327. °C. 2502(9) + 02(9) 1:; 2.503(9) 5. WhoT is The pH and The [0H] for a 0.218 M soluTion of meThylommonium chloride CH3NH3CI ? (Kb of CHaNHz = 4.4 x 104). (6 st) MA Cl-lsNUgCl 1.. gm» 0;. will»? + 0" (petal. 5633 ”go /> k +- C\>‘ N“ {CH 5%“ )l'lzou) <-*" $30 {090) 3 2 T, @266;ng X: 573M / :jff 19-. .. K“: V-b .u La?“- - '(H .3 _ fit) 1: 1% '5: "13/40", :, “so-t] lam/:9” 7"“ [0‘3 ‘1‘ will 6. A 0.50 mol sample of HX, a weak acid, is dI'SSolved in enough H20 To orm 750.0 mL of soluTion. If The r'esulTing pH of The soluTion is 3.50, whaT is The Kaof HX? (6 st) Hx l Him) €— fol QiQflL : own 0.760!» ll?‘ Bonus: The 2005 Nobel Prize in ChemisTry was given for whaT area/Type of chemical research? (2st) HinT- we Talked obouT ET in class during Chp. 16! W new ...
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