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2 Chem 16 Cmmn 3 Part I April 8, 014 ANSWERS 1. What is the assigned xidatin state f carbn in the hydrgen xalate in, HCO 4? (a) 3 (b) 4 (c) 5 (d) 6 (e) 7 H 1, O, Cx: 1x4 1; x3. Which f the fllwing statements abut entrpy is NOT expected t be true? (a) Entrpy NH 3 (l) > entrpy O (g) bth at -50ºC Entrpy f xygen is larger because it is a gas. (b) Entrpy CH 3 F(g) > entrpy CH 4 (g) It is als larger because its mlar mass is larger. (c) Entrpy water > entrpy ice (d) Entrpy disslved sugar cube in cup f cffee) > entrpy sugar cube (e) Bth cases 1 mle N at 350K: entrpy f 0 L nitrgen > entrpy f 15 L nitrgen at 5 C : H kj/ml -86 S f f HOl O g H g -1 1 Jml K Calculate the change in entrpy fr the abve reactin as written at 5 C. (a) 66 J/K (b) -66 J/K S prducts rxn Sf Sf reactants 05x131x70 37JK (c) -37J/K (d) 37 J/K (e) Nne f the abve 1 4. Calculate the apprximate G rxn at 90 C fr the abve reactin. (a) -10,000 kj (b) 400 kj H prducts rxn Hf Hf reactants kJ (c) 450 kj (d) 500 kj J kj G H TS kj K 453kJ (e) 600 kj K 1000J 5. G rxn fr a certain reactin is 10. kj. Srxn 60. J/ K. Calculate the temperature range fr which the reactin is spntaneus. (a) > 300 K (b) > 460 K (c) > 540 K (d) > 600 K (e) <300 K 60J at 98 K, G H TS ; H G TS 10, 000J 98K 7,880J K H 7,880J Fr transitin temperature: G H TS 0; T 460K S 60J/ K G < 0 fr T > 460 K rxn

3 6. The law f Dulng et Petit states that the mlar heat capacity f all metals is abut 5 J/(mlᴼC). Use it t determine an unknwn metal. When70 jules f heat are added t 14 g f the metal, its temperature increases by 13ºC? Aside, the law f Dulng et Petit cmes frm the fact that metals all take up heat r energy the same way, namely, the atms vibrate mre strngly. (a) Al (b) Ti (c) Fe (d) Ag (e) Zn q 70J 0.385J qmcst; cs mt g C 14g13 C 5J g C mlar mas x 65 g/ ml ml C 0.385J 7. What is the change in ΔE, when 800. J f heat are lst by a system as an external pressure f 1.3 atm cmpresses the system frm 10.0 t 3.0 L. (1 L atm = J) (a) 1,70 J (b) -1,70 J 101.3J w PextV 1.3atm L atm 90J (c) -791 J Latm (d) -10 J E qw800 90J 10J (e) 10 J 8. Calculate the wrk dne n the system, w, when 0.17 mles f ethyl alchl react with excess CHOH g 3O g CO g 3HOl. Pick clsest answer. xygen at 350 K. (a) -0.5 kj (b) 0.5 kj (c) 1 kj (d) 3 kj (e) 6 kj 5 nmles prduct gas - mles reactant gas ml gas fr reactin as written, ml gas 0.17 ml C H OH CHOH x ml 5 that is, fr 1 ml 5. Cnsequently, ml CH5OH 1 wpextv nrt 0.34ml 8.31J ml K K J 9. In the reactin, NOg H g N g HOl (a) O in NO (b) N in NO (c) H in H (d) O in water (e) H in water, which element is reduced? In NO, O is - (frm rules); s, N is assigned +1. In N, N is 0. S, each N in NOgains an electrn, that is, it is reduced. Aside, nly 10. Calculate the standard galvanic cell ptential, Eº, fr the half reactins given t the right. reactants can be xidized r reduced. (a) 1.07 V (b) V (c) 1.33 V (d) 0.7 V (e) -0.7 V Ag aq e Ag s 0.80V I aq I s e 0.53V Ag aq I aq Ag s I s 0.7V Half reactin Eº Ag aq e Ag s 0.80V I s e I aq 0.53V

4 11. Fr the fllwing reactin, the standard cell ptential is V. What is ΔGº? a. 9.0 kj Br l Cl aq Cl g Br aq b kj c kj Br e Br. S, n =. d kj C J e. 116 kj G nfe ml e 96, ,900J ml e C 1. Calculate the cell ptential fr the abve reactin when there is abut 0.1 ml Br, Cl 0.40 M, P Cl atm, and Br 0.0 M. Careful. (a) V (b) V (c) V (d) V (e) V x0. E E lg Q0.30 lg 0.19V n Which irn nail has the largest initial rusting rate? (a) A nail in the Sahara desert In b and c rusting is delayed (b) A partially galvanized (cated with Zn) nail drpped in dilute acid (c) A partially galvanized nail expsed t air and salt water until Zn is used up (d) A nail that has been bent and straightened several times expsed t air and salt water. (e) An undamaged nail expsed t air and salt water 14. Abut what mass f irn is plated frm a FeNO fr 100 minutes? (a) 40 g (b) 10 g (c) 80 g (d) 0 g (e) < 1 g 3 3 Fe aq e Fe s 3 3 slutin with an average current f 35.0 A 35C 60s 100 min 1ml e 1ml Fe 55.8g Fe x x x x x 40g Fe s min 1 96, 500C 3ml e ml Fe 15. What is the mst likely mde f decay f the unstable nuclide Zn-58? (a) nly electrn capture Stable Zn is Zn-65, that is, 30 p and 35 n. (b) electrn capture r psitrn emissin Zn-58 has 30 p and 8 n. S, the n t p rati needs t increase. (c) electrn emissin (d) alpha particle emissin 30 Zn 9 Cu 1 psitrn emissin (e) nly psitrn emissin Zn e Cu electrn capture

5 The Ni-X galvanic cell, where X is a hypthetical metal, is shwn t the right. The Ni reductin ptential Ni aq e Ni s E 0.5 V. The metal is: X electrde is negative as shwn in the diagram. The nickel nitrate and X(III) nitrate slutins are 1 mlar. The vltage fr the galvanic cell is 0.49 V. 16. Which f the fllwing statements is crrect fr the Ni-X galvanic cell? I = Electrns flw frm right t left thrugh the light bulb II = Electrns flw frm left t right thrugh the light bulb (a) I; the Cl ins mve frm the salt bridge t the X(NO 3 ) 3 slutin. T maintain charge neutrality (b) I; the Cl ins mve frm the salt bridge t the Ni(NO 3 ) slutin. (c) II; the Cl ins mve frm the salt bridge t the X(NO 3 ) 3 slutin. (d) II; the Cl ins mve frm the salt bridge t the Ni(NO 3 ) slutin. (e) II; the Na ins mve frm the salt bridge t the X(NO 3 ) 3 slutin. 17. What is the standard reductin ptential fr (a) 0.4 V (b) -0.4 V (c) V (d) 1.4 B (e) -0.6 V 3 X 3e X? 18. Electrlysis f an aluminum chlride slutin takes place as indicated t the right. What is the cathde reactin? Careful! (a) Cl aq Cl aq e (b) Fe aq e Fes (c) 3 Al aq 3e Al s (d) HOl e Hg OH aq (e) HOl Og 4H aq 4e Because the metal electrde is negative, electrns are generated here. S, xidatin takes at the metal electrde. 3 6 X X e E 0.74V calculated xidatin ptential Ni e Ni E 0.5V given Ni X Ni X E V given Ptentials fr water: H O l e H g OH aq E 0.83V H O l O g 4H aq 4e E 1.3V Pssibly useful reductin ptentials: Cl aq e Cl aq E 1.36V Fe aq e Fe s E 0.44V 3 Al aq 3e Al s E 1.66 V Nte, the (-) f the battery is the surce f the electrns. S, reductin takes place at the irn electrde. (a) and (e) are xidatin (b) Fe is easiest t reduce, BUT there are n Fe (d) even with vervltage water is easier t reduce than ins t reduce 3 Al (c)

6 19. In a living rganism, the decay f C-14 prduces 15.3 disintegratins per minute per gram f carbn. The half-life f C-14 is 5730 years. A bne sample with.7g f carbn has 1.3 disintegratins per minute. Abut hw ld is the bne sample in years? 1.3 D / min (a),000 yr (b) 4,000 yr (c) 6,000 yr (d) 8,000 yr (e) 10,000 yr Disintegratin rate per minute per g C 4.56 D/ min/ g.7g ln ln ln t1 yields k 1.1x10 yr k t 5,730yr R ln 4.56 ln R R ln kt yields t 1.0x10 yr 4 1 R0 k 1.1x10 yr 0. There is a nuclear reactin between 00 mles f H- and 00 mles H-3 r abut 1 kg r material. Apprximately hw much energy is released? H 1H He 0n Istpe amu r g/ml (a) 3x10 8 J (b) 3x10 10 H J (c) 3x10 1 J H (d) 3x10 14 J He (e) 3x10 16 J g n m ml H - cnsumed g 00ml H - 1kg 3x10 m E mc x x x 3.4x10 kgm s 3x10 J ml H g s 1. What is the apprximate ph f a 0.55 M HA? K a = 1 x 10-6 M. a. 5 b. 3 c. d. < 1 e. 4 HA aq H O aq H3O aq A ag I 0.55 M - ~0 0 C -x HO A x +x +x E 0.55-x x x 3 Ka; HA 0.55 x 1 10 ; x x x x M ph lg H 3.13

7 Part B (4 pints) I. The fllwing reactin will be balanced in an acidic slutin: ClO aq CN aq Cl aq CNO aq (a) (3 pts) What is ne f the balanced half-reactins? Circle: xidatin r reductin half-reactin 3 CN HO CNO H e (b) (3 pts) What is the ther balanced half-reactin? Circle: xidatin r reductin half-reactin ClO Cl 3H O 3 ClO 6H Cl 3H O 3 ClO 6H 6e Cl 3H O 3 (c) ( pts) What is the balanced reactin? N pints unless a and b are crrect. 3CN 3H O 3CNO 6H 6e ClO 6H 6e Cl 3H O 3 3CN ClO 3CNO Cl 3 (d) (4 pts) Cnvert the fllwing balanced reactin in an acidic slutin t a basic ne. Careful, hydrgen sulfate HSO 4 is a weak acid and must als be neutralized. 1 4Cl g S aq 4H O aq 8Cl aq HSO aq 7H aq 4 1 4Cl g S aq 4H O aq 8OH aq 8Cl aq HSO aq 7H aq 8OH aq 4 4Cl g S aq 4H O aq 8OH aq 8Cl aq SO aq H O aq 7H O aq 4 4Cl g S aq 8OH aq 8Cl aq SO aq 4H O aq 4

8 II. Three independent prblems. (a) (4pts) Suppse the reactin is As Bg Cs reactin at 00ºC if G rxn. What is the equilibrium cnstant fr a = kj/ml at 00ºC. INCLUDE UNITS. G 50 J / ml G RTln K; ln K RT J ml K K 8.31 / / K e atm Units are frm reactin (b) (4pts) Fr the fllwing reactin, the standard cell ptential is V. What is the equilibrium cnstant at 98K? INCLUDE UNITS. 3 Cr aq Cu s Cr aq Cu aq Each mle f Cu atms lses mles f electrns. S n =. At equilibrium, E 0 and Q K eq S, E E lg Q becmes 0 E lgk n n ne M M 9 lg K 8.4; K x10 M M difference due t rund-ff errr in each prblem Alternatively use : G nfe and G RT ln K 96500C0.84J 16, 000J G ml 16, 000 J; ln K 3.7x10 ml C 8.31J 98 K (c) (4pts) Fr the Cd-Cu galvanic cell the vltage fr standard cnditins is 0.74 V. The reactin is Cd s Cu aq Cd aq Cu s. What is the cpper (II) in cncentratin if the vltage at 98 K is 0.54 V and the [Cd + ] is 0.1 M? n (because t electrns needed fr reductin r xidatin) Cd ; lg ; lg Q E E Q Cu x n x lg 10 x ; lg x ; lg x 7.768; Cu x x10 8 M