Land final. 97 key

Land final. 97 key - §S I 98 5 Emma lt Write{NC Part I 105...

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Unformatted text preview: §S I]: 98 5 Emma lt Write/{NC Part I - 105 Pts. N0 partial credit. KK 7 l. (10 pts) For the reaction 6 C(s) + 3 H2(g) fi C6H6(l) Aern° = 49 k] at 298 K. This reaction will A. be driven by the enthalpy. D. be spontaneous at low temperatures. B. not be spontaneous at high temperatures. E. be spontaneous at all temperatures. @Ot be spontaneous at any temperature. 2. (15 pts) The relationship between the solubility in water, 5, and the Ksp for the ionic solid A1C13 is: A. Ksp=S B Ksp=3S4 C Ksp=4S3 @Ksp=27s4 E Ksp=282 3f ._ 4/6/3 :3 ,4! 2t 36/ 3 35 A? 89235)} 1 2 25" 3. (18 pts) How many grams of sodium nitrite (NaNOz, MW =68.98) must be added to a liter of 0.15 M nitrous acid (HNOz, Ka=4.3 * 10“) to make a buffer solution of pH = 4.0 ? A. 5.3 grams B. 44.5 grams C. 22.2 grams D. 80.5 grams E. 127 grams I/(a/es fle€e 5,43 #2 7% +/0 ' , [5’46 : Kev/’3 [JQfl )0 f 4 j . /0 T,{S/ Avg/0% mus/66’ [DA/00;) x 53378 2 314/. / 4. (10 pts) For the boiling of water at 100°C, / ’“l A. (Assurroundings + ASsystem) is less than zero. D. Assurroundings is positive. 13- ASsurroundings is greater than ASsystem- @Assurroundings = "Assystem- C. ASSurroundings iS leSS than ASsystem. A 6 :— 0 [thf/IZMM) AH : 7A3 M42)/ 3 5. (20 pts) What is the solubility of AgBr (Ksp = 5.0 * 10-13) in 0.10 M KBr? A. 0.10M ‘5.0* 10'12M C. 2.2*10'6M D. 50* 10'13M E. 7.0*10-7M 49%;» '33 lg)“ 52f o (7,! +x +x 1X dt/fX Sax/5‘” _~_~ 3 (mg) 46%”. 52401 Sawdmzs 45> 7/4in 6. (20 Pts) Predict what will happen when 0.010 moles of the soluble salt Cu(ClO4)2 are added to a 0.0010 M NaIO3(aq) solution. The . l“! Sp for Cu(IO3)2 IS 7. 4*10 28 ”4% Va/M(U // A. The value of Ksp increases by a factor of 0.14. D. The value of Ksp decreases by a factor of 0.14. B. NaClO4(s) will precipitate spontaneously. @o precipitation will occur. C. Cu(IO3)2 (s) will precipitate spontaneously. ~ 3’ 6%,?“ [@/o m) [ Dal/121:1 271‘ /0 504 K #0072 IMO“ 7. (12 pts) For the reaction, 2 NH3(g) :2 3 H2(g) + N2(g) Aern° = 92.22 k] and Aern°= 198.75 J K‘1 at 298 K. Estimate the temperature at which the reaction is spontaneous. A)?! : TA9 47l£g ' A/‘l‘ : 4,7 LEM/O3 <7 A5 /7S, 75 % .— ‘ A. The reaction is not spontaneous at any temperature. B. The reaction is spontaneous at all temperatures. @bove 464 K D. below 464 K E. at 273 K fly 4 16. (35 pts total) For a given biological process, a buffer solution must be capable of maintaining an aqueous solution between pH 9 and pH 8 during the addition of 20 ml of 0.2 M HCl. A researcher mixes together the following: Part II - 145 pts: Show work for partial credit. 400 ml of 0.03 M NH3 and 1.5 g NH4Cl (MW = 53.5 g/mol) The pKa for NH4+ is 9.24. a)(15 pts) What is the pH of the resulting buffer solution before addition of acid? ée. 139/72: #7424 by 4.4m? Ml: Man a; “'03 ~ 8,5? [.5 ___—-—-—- 97,55 b)(20 pts) What is the pH after the addition of the HCl? é‘fieoal- (194* a2) ), 5" ~ , 7r , 929 +603 o :2) Key/5 9.(60 pts total) Hydrogen is an ideal fuel because of its high energy content (AHcombustion) and the innocuous combustion product, water. However, hydrogen and oxygen do not react rapidly at low temperatures due to kinetic barriers to the reaction. At high temperatures, reaction does take place rapidly. The following questions illustrate the effect of temperature on the available energy from this reaction. Consider the following information: 1) H2(g)+ 1/2 02(g) r—e H200) -286 AH°f/ kJ-mol'l 131 205 70 S° /J°K‘1-mol‘1 L~/_\——A\ ’00” M‘k‘ a)(20 pts) Calculate AG?xn for reaction (I) at 400 K. A éiw, 1’ £44 Gay/wads ~ 2 a $426415, 94,0: A45: - 7am; A/J, ” : aw K7 A95 2 '90 7/02, 5+13I) =~ war Agra: "236/0flfi 3’ + @6x »/63,S‘> -Qc2/76/Dr3’ b)( 15 pts) Calculate the equilibrium constant for this reaction at 400 K. (If you were unable to claculateAG?xn in part a, use the value -3.31*105 J/mol). For comparison, AG?xn for reaction (I) at 1800 K = +8.3 x 103 J/mol and the equilibrium constant at 1800K = 0.57. Key c)(15 pts) Calculate the maximum energy obtainable to do work starting with 4 atm H2(g) and 4 atm 02(g) at 400K. Indicate whether ener is transferred into or out of the s stem. A4,; 467/2 Q Aéflm: 4L4: METAGZ Aé;; ~22/ Kj/kzo/ (flaw a) as: @%@[email protected]*@y2: “2‘3 “gm/mo + 6 /S‘ =-‘ ”WV/<7 ~ fizz/1574;»??? Ml’l‘wfi 97674?“ d)(10 points) The Aern starting with 4 atm 2(g) and 4 atm 02(g) at 1800K = -2.3 x 10 J. Using your A670; answer from part (c), decide at which temperatureyOOK or 1800K it would be more advantageous to run this reaction to do work (such as power a vehicle)? (If you did not complete part (c), use Aern(400K) = -3 x 105 J.) éaL M/a E 4);» baa/«K 4f WK“ Kg 19. (50 pts total) This problem illustrates the use of activities to accurately calculate equilibrium (:1 a. (15 pts) (a) First calculate the solubility (in moles/liter) of SnIz (Ksp=8.3*10'6) in water. Assume the ionic strength is near zero (i.e., no need to use activities). 2+ , nglé 33L +21 5 2€ (10 pts) (b) Now calculate the ionic strength of a solution that is 0.02 M in K2804 (a very soluble salt). (SnSO4 is also very soluble.) .. J, 2 ,02 “2):; 2,[)é M‘ 2500100) 4 Z >( (25 pts) (0) If the activity coefficient at the ionic strength in (b) for Sn2+ is 0.48, for K+ is 0.78, for I' is 0.78, and for 8042' is 0.43, what is the solubility of Sn12 in a 0.02 M solution of K2804? ~é_ 1t 2 2 SUMO ~ [542) X542»! [fir] biz—— : (99x24 (:23)szsz 57L ' 2 : 3%043’54192 X (”'25) ...
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