CHEM Chapter 19. Chemical Thermodynamics (Homework) Ky

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1 1. Which of these species would you expect to have the lowest standard entropy (S )? A. CH4(g) B. HF(g) C. NH3(g) D. H2O(g) 2. Which one of the following reactions would you expect to have highest S? A. CH4(g) + 2O2(g) CO2(g) + 2H2O(g) B. C2H2(g) + 5 /2O2(g) 2CO2(g) + H2O(g) C. C2H4(g) + 3O2(g) 2CO2(g) + 2H2O(g) D. C2H6(g) + 7 /2O2(g) 2CO2(g) + 3H2O(g) 3. Which response includes all the following processes that are accompanied by an increase in entropy? 1) 2SO2(g) + O2(g) SO3(g) 2) H2O(l) H2O(s) 3) Br2(l) Br2(g) 4) H2O2(l) H2O(l) + 1 /2O2(g) A. 1, 2, 3, 4 B. 1, 2 C. 2, 3, 4 D. 3, 4 E. 1, 4 1

2 4. Which response includes all of the following processes that are accompanied by an increase in entropy? 1) I2(s) I2(g) 2) 2I(g) I2(g) 3) 2NH3(g) N2(g) + 3H2(g) 4) Mg 2+ (aq) + 2OH (aq) Mg(OH)2(s) A. 1, 2 B. 1, 3 C. 3, 4 D. 3 E. 2, 4 5. Arrange these reactions according to increasing S. 1) H2O(g) H2O(l) 2) 2NO(g) N2(g) + O2(g) 3) MgCO3(s) MgO(s) + CO2(g) A. 1 < 2 < 3 B. 2 < 3 < 1 C. 3 < 2 < 1 D. 2 < 1 < 3 E. 1 < 3 < 2 6. Which of the following is expected to have zero entropy? I. N2(g) at 273 K II. SiO2(s, amorphous) at 0 K III. NaCl(s) perfectly ordered crystal at 25 K IV. Na(s) perfectly ordered crystal at 0 K A. I and IV B. III and IV C. I and II D. I, II, and III E. IV only 2

3 7. Aluminum forms a layer of aluminum oxide when exposed to air which protects the bulk metal from further corrosion. 4Al(s) + 3O2(g) 2Al2O3(s) Using the thermodynamic data provided below, calculate S for this reaction. A J/K mol B J/K mol C J/K mol D J/K mol E J/K mol 8. Determine S for the reaction SO3(g) + H2O(l) H2SO4(l). A J/K mol B J/K mol C J/K mol D J/K mol E J/K mol 3

4 9. Calculate S for the reaction SO2(s) + NO2(g) SO3(g) + NO(g). A J/K mol B J/K mol C J/K mol D J/K mol E J/K mol 10. With respect to the system only, a reaction with H < 0 and S > 0 is predicted to be: A. Spontaneous at all temperatures B. Spontaneous at high temperatures only C. Spontaneous at low temperatures only D. Nonspontaneous at all temperatures 11. Which of the following is consistent with a spontaneous endothermic reaction? A. H > 0, S < 0, G < 0 B. H > 0, S > 0, G < 0 C. H < 0, S < 0, G < 0 D. H < 0, S > 0, G > 0 E. H > 0, S < 0, G > 0 4

5 12. Ozone (O3) in the atmosphere can react with nitric oxide (NO): O3(g) + NO(g) NO2(g) + O2(g). Calculate the G for this reaction at 25 C. ( H = 199 kj/mol, S = 4.1 J/K mol) A kj/mol B kj/mol C kj/mol D kj/mol E. 198 kj/mol 13. For the reaction H2(g) + S(s) H2S(g), H = 20.2 kj/mol and S = J/K mol. Which of these statements is true? A. The reaction is only spontaneous at low temperatures. B. The reaction is spontaneous at all temperatures. C. G becomes less favorable as temperature increases. D. The reaction is spontaneous only at high temperatures. E. The reaction is at equilibrium at 25 C under standard conditions. 14. The normal boiling point of acetic acid is C. If a sample of the acetic acid is at C, predict the signs of H, S, and G for the boiling process at this temperature. A. H > 0, S > 0, G < 0 B. H > 0, S > 0, G > 0 C. H > 0, S < 0, G < 0 D. H < 0, S > 0, G > 0 E. H < 0, S < 0, G > Calculate the equilibrium constant for the decomposition of water 2H2O(l) 2H2(g) + O2(g) at 25 C, given that G f (H2O(l)) = kj/mol. A B C D E

6 16. Nitrosyl chloride (NOCl) decomposes at elevated temperatures according to the equation 2NOCl(g) 2NO(g) + Cl2(g). Calculate Kp for this reaction at 227 C. ( H = 81.2 kj/mol, S = 128 J/K mol) A B C D E For the reaction 2 SO2(g) + O2(g) 2 SO3(g), if initially P(SO2) = 1.2 atm, P(O2) = 1.8 atm, and P(SO3) = 2.1 atm, calculate G for this reaction at 25 C. The following data is valid at 25 C: A kj/mol B kj/mol C kj/mol D. 1,174.7 kj/mol E kj/mol 6

7 18. For the reaction 2NO(g) + O2(g) 2NO2(g) if initially P(NO) = 1.5 atm, P(O2) = 1.4 atm, and P(NO2) = 2.0 atm, calculate G for this reaction at 25 C. The following data is valid at 25 C: A kj/mol B kj/mol C kj/mol D kj/mol E kj/mol 19. Determine the equilibrium constant (Kp) at 25 C for the reaction CO(g) + H2O(g) CO2(g) + H2(g). G = 28.5 kj/mol A B C. 1.2 D E The solubility product constant at 25 C for AgI(s) in water has the value Calculate Grxn at 25 C for the process AgI(s) Ag + (aq) + I (aq) where [Ag + ] = and [I ] = A kj/mol B kj/mol C. 0.0 kj/mol D kj/mol E. 4.4 kj/mol 7

8 21. Predict the normal boiling point of triethylborane (C6H15B) using the following data: A. 92 C B. 21 C C. 21 C D. 365 C E. 256 C 22. For the reaction HCONH2(g) NH3(g) + CO(g), Kc = 4.84 at 400 K. If H for this reaction is 29 kj/mol, find Kc at 500 K. A. 5.8 B C. 27 D E In the gas phase, methyl isocyanate (CH3NC) isomerizes to acetonitrile (CH3CN), H3C N C (g) H3C C N (g) with H = 89.5 kj/mol and G = 73.8 kj/mol at 25 C. Find the equilibrium constant for this reaction at 100 C. A B C D E

9 24. Using the thermodynamic data provided below, calculate the standard change in entropy when one mole of sodium sulfate is dissolved in water. Will the solubility of sodium nitrate increase or decrease if the temperature of the system is increased? A J/K mol; solubility decreases with increasing temperature B J/K mol; solubility increases with increasing temperature C J/K mol; solubility decreases with increasing temperature D J/K mol; solubility increases with increasing temperature 25. Assuming S and H do not vary with temperature, at what temperature will the reaction shown below become spontaneous? C(s) + H2O(g) H2(g) + CO(s) ( S = J/K mol; H = kj/mol) A. 670 C B. 690 C C. 710 C D. 730 C 26. Rubidium has a heat of vaporization of 69.0 kj/mol at its boiling point (686 C). Calculate S for this process, Rb(l) Rb(g), at 1 atm and 686 C. A J/K mol B J/K mol C J/K mol D J/K mol 9

10 27. The free energy of formation of nitric oxide, NO, at 1000 K (roughly the temperature in an automobile engine during ignition) is about 78 kj/mol. Calculate the equilibrium constant Kp for the reaction N2(g) + O2(g) 2NO(g) at this temperature. A. Kp = B. Kp = C. Kp = D. Kp = Predict the signs (, +, or 0) of H and S, in that order, for the reaction: 6CO2(g) + 6H2O(g) C6H12O6(g) + 6O2(g). A. +, B. 0, + C. +, + D., 29. What is the free energy change for the reaction SiO2(s) + Pb(s) PbO2(s) + Si(s)? G f (PbO2) = 217 kj/mol G f (SiO2) = 856 kj/mol A. 619 kj/mol B. 639 kj/mol C. 659 kj/mol D. 679 kj/mol 30. The heat of vaporization of water is 2.27 kj/g. What is Svap per mole at the normal boiling point? A J/K mol B J/K mol C J/K mol D J/K mol 10

11 31. The following reaction is nonspontaneous at 25 C: Cu2O(s) 2Cu(s) + 1 /2O2(g), G = 141 kj/mol If S = 75.8 J/K mol, what is the lowest temperature at which the reaction will be spontaneous? A K B K C K D K 32. Select True or False: The reaction 3H2(g) + N2(g) 5.0 mol H2 are mixed in a 2.5 L reactor. 2NH3(g), Kc = 9.0 at 350 C proceeds from right to left when 1.0 mol NH3, 5.0 mol N2, and True False 33. Consider the reaction CO(g) + 2H2(g) CH3OH(l) at 25 C. G f (CO) = kj/mol G f (CH3OH) = kj/mol H f (CO) = kj/mol H f (CH3OH) = kj/mol S (CO) = J/K mol S (CH3OH) = J/K mol Calculate G at 25 C. A kj/mol B kj/mol C kj/mol D kj/mol 34. Select True or False: At a given temperature, O2(g) at 5 atm has a higher entropy per mole than O2(g) at 0.5 atm. True False 11

12 35. Hvap for ethanol is 38.7 kj/mol at its boiling point (78 C). What is Ssurr when 1.00 mole of ethanol is boiled? A. 310 J/K mol B. 210 J/K mol C. 110 J/K mol D. 100 J/K mol 36. Sulfur can be separated from lead in the mineral galena, PbS(s), by "roasting" the ore in the presence of oxygen as shown in the following reaction: 2PbS(s) + 3O2(g) 2PbO(s) + 2SO2(g) Determine G for the above reaction at 850 C. A. 620 kj/mol B. 640 kj/mol C. 660 kj/mol D. 680 kj/mol 37. Given the following data, calculate the boiling point of HCOOH (formic acid). A. 115 C B. 125 C C. 145 C D. 165 C 12

13 38. Using the thermodynamic data provided below, calculate Ka1 for H2CO3(aq) at 25. A B C D Select True or False: Melting an ionic solid always results in an increase in entropy. True False 40. Select True or False: Dissolving an ionic solid in water always results in an increase in entropy. True False 13

14 Key 1. B 2. D 3. D 4. B 5. A 6. E 7. D 8. C 9. C 10. A 11. B 12. E 13. B 14. A 15. B 16. A 17. C 18. B 19. D 20. C 21. A 22. C 23. B 24. A 1

15 25. C 26. D 27. B 28. A 29. B 30. D 31. A 32. FALSE 33. A 34. FALSE 35. C 36. C 37. A 38. C 39. TRUE 40. FALSE 2