Chem 1412 SU06 Exam 4

Chem 1412 SU06 Exam 4 Student: 1. Which of the following is necessary for a process to be spontaneous? A. H sys < 0 B. S sys > 0 C. S surr < 0 D. S univ > 0 E. G sys = 0 2. Which of the following is always true for an exothermic process? A. q sys > 0, S surr < 0 B. q sys < 0, S surr > 0 C. q sys < 0, S surr < 0 D. q sys > 0, S surr > 0 E. w < 0 3. Which, if any, of the following processes is spontaneous under the specified conditions? A. H 2 O(l) H 2 O(s) at 25 C B. CO 2 (s) CO 2 (g) at 0 C C. 2H 2 O(g) 2H 2 (g) + O 2 (g) D. C(graphite) C(diamond) at 25 C and 1 atm pressure E. None of these is spontaneous. 4. Which relationship best describes S for the following reaction? CO(g) + H 2 O(g) CO 2 (g) + H 2 (g) A. S = H B. S = H /T C. S > 0 D. S < 0 E. S 0 Page 1

5. Which relationship or statement best describes S for the following reaction? C 2 H 5 OH(l) + 3O 2 (g) 2CO 2 (g) + 3H 2 O(l) A. S 0 B. S < 0 C. S > 0 D. S = H /T E. More information is needed to make a reasonable prediction. 6. Which of the following pairs has the member with the greater molar entropy listed first? All systems are at 25 C. A. CO(g), CO 2 (g) B. NaCl(s), NaCl(aq) C. H 2 S(g), H 2 S(aq) D. Li(s), Pb(s) E. H 2 (g), H 2 O(g) 7. In which one of the following pairs will the first system have a higher entropy than the second? Assume P and T are the same for each pair, unless stated otherwise. A. 1 mole He(g); 1 mole Kr(g) B. 1 mole O 2 (g); 2 mole O(g) C. 1 mole CH 4 (g); 1 mole C 2 H 6 (g) D. 1 mole Xe(g) at 1 atmosphere; 1 mole Xe(g) at 0.5 atmosphere E. 20 one-dollar bills distributed randomly among 20 people; 20 one-dollar bills distributed randomly among 10 people 8. Calculate S for the reaction 2Cl 2 (g) + SO 2 (g) SOCl 2 (g) + Cl 2 O(g) Substance: Cl 2 (g) SO 2 (g) SOCl 2 (g) Cl 2 O(g) S (J/K mol): 223.0 248.1 309.77 266.1 A. -118.2 J/K B. -104.8 J/K C. 104.8 J/K D. 118.2 J/K E. 1270.0 J/K Page 2

9. For a chemical reaction to be spontaneous only at low temperatures, which of the following conditions must be met? A. S > 0, H > 0 B. S > 0, H < 0 C. S < 0, H < 0 D. S < 0, H > 0 E. G > 0 10. Consider the following quantities used in thermodynamics: E, H, q, w, S, G. How many of them are state functions? A. 0 B. 1 C. 2 D. 3 E. 4 11. Elemental boron can be formed by reaction of boron trichloride with hydrogen. BCl 3 (g) + 1.5H 2 (g) B(s) + 3HCl(g) Calculate G for the reaction. Substance: BCI 3 (g) H 2 (g) B(s) HCl(g) G f (kj/mol): -388.7 0 0-95.3 A. -293.4 kj B. 293.4 kj C. -102.8 kj D. 102.8 kj E. none of these choices is correct Page 3

12. Nitric oxide reacts with chlorine to form NOCl. The data refer to 298 K. 2NO(g) + Cl 2 (g) 2NOCl(g) Substance: NO(g) Cl 2 (g) NOCl(g) H f (kj/mol): 90.29 0 51.71 G f (kj/mol): 86.60 0 66.07 S (J/K mol): 210.65 223.0 261.6 What is the value of G for this reaction at 550 K? A. -143.76 kj B. -78.78 kj C. -22.24 kj D. -10.56 kj E. 66600 kj 13. Consider the figure below which shows G for a chemical process plotted against absolute temperature. Which one of the following is an incorrect conclusion, based on the information in the diagram? A. H > 0 B. S > 0 C. The reaction is spontaneous at high temperatures. D. S increases with temperature while H remains constant. E. There exists a certain temperature at which H = T S. Page 4

14. Iron(III) oxide can be reduced by carbon monoxide. Fe 2 O 3 (s) + 3CO(g) 2Fe(s) + 3CO 2 (g) Use the following thermodynamic data at 298 K to determine the equilibrium constant at this temperature. Substance: Fe 2 O 3 (s) CO(g) Fe(s) CO 2 (g) H f (kj/mol): -824.2-110.5 0-393.5 G f (kj/mol): -742.2-137.2 0-394.4 S (J/K mol): 87.4 197.7 27.78 213.7 A. 7.0 10-6 B. 1.3 10-3 C. 2.2 10 4 D. 1.4 10 5 E. > 2.0 10 5 15. Use the thermodynamic data at 298 K below to determine the K sp for barium carbonate, BaCO 3 at this temperature. Substance: Ba 2+ (aq) CO 3 2- (aq) BaCO 3 (s) H f (kj/mol): -538.36-676.26-1219 G f (kj/mol): -560.7-528.1-1139 S (J/K mol): 13-53.1 112 A. 5.86 B. 6.30 10 8 C. 1.59 10-9 D. 5.47 10-21 E. 2.18 10-27 Page 5

16. Consider the reaction CuO(s) + H 2 (g) Cu(s) + H 2 O(l) In this reaction, which substances are the oxidant and reductant, respectively? A. CuO and H 2 B. H 2 and CuO C. CuO and Cu D. H 2 O and H 2 E. none of these choices is correct 17. When the following redox equation is balanced with smallest whole number coefficients, the coefficient for zinc will be. Zn(s) + ReO - 4 (aq) Re(s) + Zn 2+ (aq) (acidic solution) A. 2 B. 7 C. 8 D. 16 E. none of these choices is correct 18. Which of the following statements about voltaic and electrolytic cells is correct? A. The anode will definitely gain weight in a voltaic cell. B. Oxidation occurs at the cathode of both cells. C. The free energy change, G, is negative for the voltaic cell. D. The electrons in the external wire flow from cathode to anode in an electrolytic cell. E. None of these statements is correct. Page 6

19. A voltaic cell is prepared using copper and silver. Its cell notation is shown below. Cu(s) Cu 2+ (aq) Ag + (aq) Ag(s) Which of the following processes occurs at the cathode? A. Cu(s) Cu 2+ (aq) + 2e - B. Cu 2+ (aq) + 2e - Cu(s) C. Ag(s) Ag + (aq) + e - D. Ag + (aq) + e - Ag(s) E. Cu(s) + 2Ag + (aq) Cu 2+ (aq) + 2Ag(s) 20. What is the E cell for the cell represented by the combination of the following half-reactions? 2Hg 2+ (aq) + 2e - Cr 3+ (aq) + 3e - Hg 2 2+ (aq); E = 0.92 V Cr(s); E = -0.74 V A. -0.18 V B. 0.18 V C. 1.28 V D. 1.66 V E. 2.12 V 21. Examine the following half-reactions and select the strongest oxidizing agent among the substances. [PtCl 4 ] 2- (aq) + 2e - Pt(s) + 4Cl - (aq); E = 0.755 V RuO 4 (s) + 8H + (aq) + 8e - Ru(s) + 4H 2 O(l); E = 1.038 V FeO 2-4 (aq) + 8H + (aq) + 3e - Fe 3+ (aq) + 4H 2 O(l); E = 2.07 V H 4 XeO 6 (aq) + 2H + (aq) + 2e - XeO 3 (aq) + 3H 2 O(l); E = 2.42 V A. [PtCl 4 ] 2- (aq) B. RuO 4 (s) C. HFeO 4 - (aq) D. H 4 XeO 6 (aq) E. Cl - (aq) Page 7

22. Examine the following half-reactions and select the weakest reducing agent among the substances. Cr(OH) 3 (s) + 3e - Cr(s) + 3OH - (aq); E = -1.48 V SnO 2 (s) + 2H 2 O(l) + 4e - Sn(s) + 4OH - (aq); E = -0.945 V MnO 2 (s) + 4H + (aq) + 2e - Mn 2+ (aq) + 2H 2 O(l); E = 1.224 V Hg 2 SO 4 (s) + 2e - 2Hg(l) + SO 2-4 (aq);e = 0.613 V A. Cr(s) B. Sn(s) C. Mn 2+ (aq) D. Hg(l) E. OH - (aq) 23. When metal A is placed in a solution of metal ions B 2+, a reaction occurs between A and B 2+, and metal ions A 2+ appear in the solution. When metal B is placed in acid solution, gas bubbles form on its surface. When metal A is placed in a solution of metal ions C 2+, no reaction occurs. Which of the following reactions would not occur spontaneously? A. C(s) + 2H + (aq) H 2 (g) + C 2+ (aq) B. C(s) + A 2+ (aq) A(s) + C 2+ (aq) C. B(s) + C 2+ (aq) C(s) + B 2+ (aq) D. A(s) + 2H + (aq) H 2 (g) + A 2+ (aq) E. B(s) + 2H + (aq) H 2 (g) + B 2+ (aq) 24. The following half-reactions occur in the mercury battery used in calculators. If E cell = 1.357 V, calculate the equilibrium constant for the cell reaction at 25 C. (Assume the stoichiometric coefficients in the cell reaction are all equal to 1.) HgO(s) + H 2 O(l) + 2e - ZnO(s) + H 2 O(l) + 2e - Hg(l) + 2OH - (aq) Zn(s) + 2OH - (aq) A. 9.4 10 22 B. 7.5 10 45 C. 6.4 10 63 D. 7.8 10 91 E. > 9.9 10 99 Page 8

25. Calculate G for the oxidation of 3 moles of copper by nitric acid. Cu 2+ (aq) + 2e - Cu(s); E = 0.34 V NO - 3 (aq) + 4H + (aq) + 3e - NO(g) + 2H 2 O(l); E = 0.957 V A. -120 kj B. -180 kj C. -240 kj D. -300 kj E. -360 kj 26. A voltaic cell consists of a Mn/Mn 2+ electrode (E = -1.18 V) and a Fe/Fe 2+ electrode (E = -0.44 V). Calculate [Fe 2+ ] if [Mn 2+ ] = 0.050 M and E cell = 0.78 V at 25 C. A. 0.040 M B. 0.24 M C. 1.1 M D. 1.8 M E. none of these choices is correct 27. A concentration cell consists of two Zn/Zn 2+ electrodes. The electrolyte in compartment A is 0.10 M Zn (NO 3 ) 2 and in compartment B is 0.60 M Zn(NO 3 ) 2. What is the voltage of the cell at 25 C? A. 0.010 V B. 0.020 V C. 0.023 V D. 0.046 V E. none of these choices is correct 28. Which, if any, of the following metals would not be capable of acting as a sacrificial anode when used with iron E Fe = -0.44 V; all E values refer to the M 2+ /M half-cell reactions. A. manganese, Mn, E = -1.18 V B. cadmium, Cd, E = -0.40 V C. magnesium, Mg, E = -2.37 V D. zinc, Zn, E = -0.76 V E. All of these metals are capable of acting as sacrificial anodes with iron. Page 9

29. What mass of silver will be formed when 15.0 A are passed through molten AgCl for 25.0 minutes? A. 0.419 g B. 6.29 g C. 12.6 g D. 25.2 g E. 33.4 g 30. A current of 250. A flows for 24.0 hours at an anode where the reaction occurring is Mn 2+ (aq) + 2H 2 O(l) MnO 2 (s) + 4H + (aq) + 2e - What mass of MnO 2 is deposited at this anode? A. 19.5 kg B. 12.9 kg C. 4.87 kg D. 2.43 kg E. none of these choices is correct Page 10

Chem 1412 SU06 Exam 4 Key 1. (p. 870) D 2. (p. 877) B 3. (p. 870) B 4. (p. 875) E 5. (p. 875) B 6. (p. 874) C 7. (p. 874) E 8. (p. 876) A 9. (p. 887) C 10. (p. 881) E 11. (p. 884) D 12. (p. 887) D 13. (p. 887) D 14. (p. 892) D 15. (p. 892) C 16. (p. 904) A 17. (p. 907) B 18. (p. 908) C 19. (p. 912) D 20. (p. 915) D 21. (p. 918) D Page 1

22. (p. 918) C 23. (p. 917) C 24. (p. 925) B 25. (p. 925) E 26. (p. 927) C 27. (p. 930) C 28. (p. 938) B 29. (p. 946) D 30. (p. 946) E Page 2