Exam 4 2007 KEY - CHM 131 1 Exam#4 CodeName a Page 2 of l...

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Unformatted text preview: CHM 131 1: Exam #4 November 20, 2007 CodeName a Page 2 of l l CHM 1311: General Chemistry 1, Fall 2007 Exam #4, November 20, 2007 CodeName (print) i For ALL problems: (1) SHOW ALL WORK TO GET FULL CREDIT (2) Put the answer in the box or blank if provided (3) Obey rules regarding significant figures (4) Write units for all numerical answers ' Useful equations and constants universal gas constant R = 0.0821 Latm mol_1K‘l = 8.314Jmor11CI pressure units: 1 atm = 14.7 lb in‘2 (atm pressure at sea level) = 101,325 pascals (exactly) = 760.0 torr = 760.0 mm Hg = 1.01325 bar 1joule= 1 kg mzs—z 1 cal = 4.184J standard molar volume of ideal gas = 22.41 L L DO NOT WRITE IN THESE BLANKS 1. (6) 11- (5) 2. (6) 12- (3) “L. 3. (6) 13. (7) 4. (4) E ‘14. (2) x 5. (6) 15. (5) 6. (5) 16- (7) K 7. (7) 17. (6) 8. (6) 13- (7) x. 9. (3) 19- (3) R 10. (6) TOTAL (100) CHM 1311: Exam #4 November 20, 2007 CodeName Page 3 of 11 1. (6 pts) A 4.40 g piece of solid CO2 (dry ice) is allowed to vaporize in a balloon. The final volume of the balloon is 1.00 L at 300. K. What is the pressure of the gas? a .46 atm F: 7‘ b. 246 atm \j: QOQ c. 0.122 atm T: 300‘ K d. 122 atm ’ 9\ n- 04Hma B: Mloomolt e. none of these Ll‘l-Oli) Wimp) Egg: (oioomomoml 40m 30M : 2.01., MM V 0-0010 ________________________.__._—_.————————————-————— 2. (6 pts) The molar enthalpy of combustion of ethanol (CZHSOH) is -1409 k]. What is the standard enthalpy change for the following process? 4C02 (g) + 6H20(1) -) 2C2H50H (g) + 602 (g) . a. —1409kJ *5 b. 1409kJ 03 CZ “SOHC‘AB {303033 aZCOZC®+ SHZOCQ l3 0- “231W -TO GET weer tum; MUST? 2818kJ a) [YEW WM U) a :) + 1‘10“! KS e. notenough information MUJIM 03 2X: :7 26‘”qu M) D 3. (6 pts) A sample of ideal gas occupies 5.00 L at 27.0 °C and 62.5 torr. Calculate the volume the gas would occupy at 177.0 °C and 375 torr. \j \s .— Pl 1 217?, 7: =7 V2" Ft“! ‘Z a. 45.0L z P T v—f’r’“ b. 22.5L TX: 200°C " 7' 172 l I c. 5.00L p‘ :(,Z.S+,orr \12: ((925er gooqmowaswz) d. 2.50L —————/ 1.25L V7,; 7' (3”§£°MLZ').O+Z‘BJSK) TL: ~ .5 Fl: KE‘I CHM 1311: Exam #4 November 20, 2007 CodeName Page 4 of 11 4. (4 pts) A chemical reaction that is used to do 55 J of work also releases 20 J of heat to the surroundings. What is the change in internal energy for this reaction? a. 35] (A) z #813 T b, —35J CL; — 203— c. 75] ;q/+N : (“20:6 +£~g§3> ‘75] = «393' e. not enough information is given 5. (6 pts) Calculate AH° for the reaction: CO2 (g) + 2 H25 (g) 9 CS2 (l) + 2 H20 (1) w Ang a ZCAHsEBW {Mm b. 472.5 k] c. —896.7 kJ = (“€433 1‘ ZéZQEflB ‘(3613‘83 T 26-203) KS (1. —264.1kJ e. ~68.3kJ z “L‘KH KS ___________________._______.————————————— 6. (5 pts) Use the ideal gas law to predict the relationship between n and T in a system of constant pressure and volume: W : NET a. n a T W [email protected]_:®~5mNr c. n/T = constant K d. PT = nRV e. PV/T = R T T CHM1311: Exam#4 PageS ofll CodeName KEY \ L 7. (7 pts) An unknown compound is vaporized at 100.0 °C to fill a 25.0 mL container at a pressure of 0.987 atm. If the vapor has a mass of 0.0564 g, what is the molecular mass of the compound? a. ssogmoi—l T: IOO-O‘C wists : 3‘7316 K H b. 18.8ng1"1 \I: : c. 22.2gmol“1 P: M955: O'Ogmorl Pu: mu“ => n: PU r; (oaswmflomswl c. 60.0 g mol'1 E‘T— > - ‘ Waxg'BiSK 1;,”le = 8.0834 9th . _ Canaan/t 56-85;;me I70. 0 3/,“00/ _ 8. (6 pts) Calculate AH° for the following reaction: 2 NH3 (g) + C02 (g) -) CO(NH2)2 (s) + H20 (1) (9/ O 6 a- w AHW (~333.H\+(~Z8Sfil{Mini-313.8) b. ~179.4 U @1332 k] s d. 133.2 k] e. —1105.0 k] f. 1105.0 k] 9. (3 pts). For which one of the following is the standard enthalpy of formation zero? 7/0 ‘ a. o (g) I b. CH4 (g) 0. CH2 (g) N2 (g) e. none of the above CHM 1311: Exam #4 November 20, 2007 CodeName Page 6 of 11 10. (6 pts) What is the density of N2 at 25.0 °C and 1 bar pressure? __ l W 2:, I} D64ng 5 a. 0.312 gL—l ll QBMLX Lows ML 0.0%‘1’2/3 TM Mme b. 0.625 L“ v g T : 250°C +2315 = 208-15 K c. 0.800 g L‘lk @113gL‘1 ?\l: nil/T “> D. .: P :; (0351323 11le V V ‘ X'QVJ‘CYZQSQSQ e. 1.60 g L“ 11. (5 pts) Calculate the specific heat of a certain unknown metal, if it requires 195 joules of heat to raise the temperature of 12.1 grams of this metal by 346° C: a. 0.541 J g_1C'1 Cl: (QM-\(VMSQLAT a b. 0.714Jg_1C_1 HSU’ :(SMBUZJSBCSM. C) @0465 J g‘1 C1 d. 0.816] g‘1 C1 e. None of the above 12. (3 pts) For which of the following reactions would the heat of reaction be labeled AHf"? a. N2 (g) + Cl2 (g) + 2H2 (g) 9 2NH4C1 (s) b. SrO (s) + SO2 (g) 9 SrSO3 (S) @Al (0 + 3/2040 + 3/2H2<g) -> A1<0H)3(s> d. 1/2 N20 (g) + 1/4 02 (g) '9 NO(g) 6- C2H2 (g) + H2 (2) 9 C2H4(g) KB“! CHM 1311: Exam #4 November 20, 2007 CodeName Page 7 of 11 13. (7 pts) The thermochemical equation for the formation of mercury (II) oxide is: 1/2 02 (g) + Hg (1) -) HgO (3) AH; = —90.8 kJ mol"1 How much heat is released when 32.5 g of Hg is reacted with excess oxygen? 19:72:: GHQ hill. :0le Mill c. 40.0w zm'bfi d. 71.8kJ e. 20.510 (“405? f BPNLMOUB 3 ~l"l.ri KT 14. (2 pts) Which one of the following is true concerning enthalpy? a. It is an intensive property, always having the units energy per mole /b./ The sign of enthalpy change of a reaction is same for both directions @It is a state function /d./ It is measured under conditions of constant volume /e./ The enthalpy change of a reaction is measured experimentally using a bomb calorimeter 15. (5 pts) Gold has a specific heat of 0.129 J g"1 C1. If 5.00 g of gold initially at 20.0 °C absorbs 1.33 J of heat, what is the final temperature of the gold? ,a/ 9.69 °c CL : (EHXWYAT) 22-0“ l.%31:(o.1z%<r/3°C\(soo3\(TF mom) 0. 30.31 °C ‘ C {yr )2 6‘ /d./20.0K 333' < 0W F " ~ (T: :2 CL C /e./17.94°C T? z 22 O ‘ o I CHM 1311: Exam #4 November 20, 2007 CodeName Page 8 of 11 16. (7 pts) A coffee cup calorimeter contains 150.0 g of water at 24.6 °C. A 110.0 g block of molybdenum metal is heated to 100.0°C and placed in water. The contents of the calorimeter come to an average temperature of 28.0 °C. What is the specific heat of molybdenum (assume no energy is lost to the calorimeter or surroundings)? 63 a. 0.064] g“ C‘1 Viki: Henge) ZI§3.‘€‘1 0.27 J g’1 C" (é .Hbmo U KLO flylmgfl QC) =(H,[8Lfi’/%o()0mgsyqul%oc§ —1 1 c. 0.81 J g C Emma“) 6N§ d. 0.15Jg"1C'1 “L 17. (6 pts) Given the following: Q 2CuO(s) -) 2Cu(s) + 02 (g) AH° = 314.6 kJ determine the heat of formation of CuO (s): (£3) a. —314.6 k] \I _ i b. 314.6kJ Cub3+ ZGZGS ‘9 CWOCQ 157.31g 'TO 691’ TMS 2m Ffwm Weunm: @Qsm k] (4‘) W 0106mm 0? U) " 3H. L Us bwuse m 2, “mtg/z, e. not enough information given CHM 1311: Exam #4 November 20, 2007 CodeName Page 9 of 11 18. (7 pts) Given the following thermochemical equations: Mn02(s) + CO (g) -) MnO(s) + CO2 (g) AH=—151kJ Mn304(s) + CO (g) 9 3 MnO(s) +. C02 (g) AH=—54 kJ 3 ano3 (s) + CO (g) -) 2Mn304(s) + C02 (g) AH=—142kJ calculate AH for the following reaction: 2MnO2 (s) + CO (g) -) Mn203 (S) + C02 (g) arm-w zmyez/m ma 1%» Jrng 2W6 EA b) 218.7kJ L2264.8ki % M (Sufi/cai33—y M“ “9+ ELIE/(bl £0”) [E 3:33: ’M3*%3 -3 to 373562631 J“ W)” We) WVMA Ew‘lsoim l' 33.95% ZMnOwy ‘l’ *‘7 4, ( A 5‘2“? K3— 19. (3 pts) Your body can cool itself by perspiring. Specifically, the reaction: H20 (1) 9 H20 (g) cools your skin when water evaporates from your body into the air. Is this transformation an endothermic or an exothermic process? r exothermic (circle one) - Coops gm Jso 96306195 new PM and,s> WWL ...
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