C1404 Spring 1998 Exam 3 Key

Note: Question 20 is not being counted in the exam.

1. Which of the following is always true for an adiabatic process?

(1) q is zero
(2) w is zero
(3) DE is zero
(4) DS is zero
(5) None of the above is true

2. Which of the following is true of DSuniverse for the process of freezing water at 0°C and 1.00 atm?

(1) DSuniverse < 0
(2) DSuniverse = 0
(3) DSuniverse > 0
(4) DSsystem > 0
(5) More data are necessary

3. Consider the expansion of a gaseous system from a region of high pressure into a vacuum. For this process:

(1) DG > 0
(2) DSuniverse = 0
(3) DSsystem > 0
(4) all of the above are correct
(5) none of the above is correct

4. Which of the following is necessarily true of an exothermic reaction at constant temperature:

(1) the entropy of the system increases
(2) the entropy of the surroundings increases
(3) the entropy of the universe increases
(4) all of the above
(5) none of the above

5. For a reaction that is exothermic and has a negative value of DS ....

(1) higher temperatures favor product formation
(2) lower temperatures favor product formation
(3) product formation is favored at all temperatures
(4) the reaction will not be product-favored at any temperature
(5) none of the above is correct

6. What is the value of DG° at 298K for a reaction which has an equilibrium constant of 3.82 at that temperature?

(1) -9460J (2) -3320 J (3) +3320 J (4) +9460 J (5) -1440J

7. Based on comparison of DG° values at 298K, trans-2-butene is more stable than cis-2-butene by about 4 kJ/mol. Therefore, the equilibrium constant for the isomerization at that temperature must be...

cis-2-butene <=> trans-2-butene
(1) 0.02 (2) 0.20 (3) 5.0 (4) 41 (5) 481

8. What are the signs of DS and DG, respectively, for the combustion of propane, an exothermic reaction?

C3H8(g) + 5 O2(g) 3 CO2(g) + 4 H2O(g)
(1) + and - (2) - and + (3) + and + (4) + and impossible to predict without knowing T (5) none of the above is correct

9. Given that DG°f = +98.2 kJ/mol for N2O4(g) and DG° for the decomposition of N2O4 according to the following equation is +5.4 kJ, all at 298 K:

N2O4(g) <=> 2 NO2(g)
Calculate DG°f for NO2(g).
(1) +46.4 kJ/mol (2) +51.8 kJ/mol (3) +92.8 kJ/mol (4) +103.6 kJ/mol (5) -103.6 kJ/mol

10. For which of the following reactions is DS > O?

(1) NH4NO3(s) NH4NO3(aq)
(2) Cl2(g) Cl2(liq)
(3) 2 NO2(g) N2O4(g)
(4) H2O(g) H2O(s)
(5) none of the above is correct

11. The algebraic signs of DH° and DS° for the electrolysis of liquid water at 298 K to give gaseous oxygen and hydrogen are....

(1) DH° > 0, DS° > 0
(2) DH° > 0, DS° < 0
(3) DH° < 0, DS° < 0
(4) DH° < 0, DS° > 0
(5) none of the above is correct

12. In the equation for the reaction of potassium iodide (KI) and sulfuric acid (H2SO4), which is true? 8KI + 9H2SO4 4I2 + 8KHSO4 + H2S + 4H2O

(1) The reducing agent is H2SO4.
(2) The oxidizing agent is KI.
(3) The substance reduced is H2SO4.
(4) The substance oxidized is KHSO4.
(5) No substances are oxidized or reduced.

13. During the demonstration of the electrolysis of aqueous (sodium chloride, sodium sulfate) solutions respectively, the anode reaction produces ......

(1) oxygen, oxygen
(2) oxygen and chlorine, oxygen
(3) chlorine, oxygen
(4) chlorine and hydrogen, oxygen
(5) hydrogen, oxygen

14. The reduction of aqueous copper (II) with iron metal has an DE° value of 0.78 V:

Fe(s) + Cu2+ (aq, 1M) <=> Fe2+ (aq, 1 M) + Cu(s)
If the standard reduction potential for Cu2+ + 2 e- <=> Cu(s) is 0.34 V, then the standard reduction potential for Fe2+/Fe(s) must be...
(1) 0.44 V (2) -0.44 V (3) 0.22 V (4) -0.22 V (5) 0.88 V

15. For the oxidation-reduction reaction described in the preceding problem (14), the equilibrium constant is.........

(1) 3.63 X 10-27 (2) 2.64 X 101 (3) 1.66 X 1013 (4) 8.23 X 1014 (5) 2.76 X 1026

16. A Daniell cell is constructed with Zn and Cu electrodes immersed in 1 molar solutions of Zn2+ and Cu2+, respectively. Given that the standard reduction potential for Cu2+/Cu(s) is 0.34 V and the standard reduction potential for Zn2+/Zn(s) is -0.76 V, we can conclude that:

(1) DG° = 81 kJ/mol
(2) DG° = -81 kJ/mol
(3) DG° = 0
(4) DG° = 212 kJ/mol
(5) DG° = -212 kJ/mol

17. A given amount of electric charge deposits 2.159 g of silver from an Ag+ solution. What mass of copper from a Cu2+ solution will be deposited by the same quantity of electric charge?

Atomic Molar Masses: Ag 107.9 g mol-1; Cu 63.5 g mol-1
(1) 0.635 g (2) 1.27g (3) 1.97 g (4) 2.54 g (5) 63.5 g

18. Based on the following information, which statement is correct?

[H+] = 1.0 M initially, PO2 = 1.0 atm
4e- + O2(g) + 4H+(aq) = 2H2O(liq) E° = 1.23 V (1) n = l, since one mole of oxygen is being considered.
(2) Addition of base should result in an E° value which is less than 1.23 V.
(3) E is independent of the pH of the solution.
(4) Q = [H2O]2 / [O2] [H+]
(5) Q = 1 / [H+]

19. Comparing the entropy of vaporization for benzene, ethanol and water at their respective boiling points, the order of increasing value is....
(1) C6H6 < C2H5OH < H2O
(2) C2H5OH < H2O < C6H6
(3) H2O < C6H6 < C2H5OH
(4) H2O < C2H5OH < C6H6
(5) C6H6 < H2O < C2H5OH

Please disregard question 20.
20. If the entropy of vaporization for carbon tetrachloride is 30.8 kJ/mol, then the normal boiling point is approximately......

(1) 0°C (2) 37°C (3) 77°C (4) 154°C (5) 350°C

21. The best answer from among the following for a graphical representation of the the temperature dependence of the equilibrium constant is that.....
(1) the line labeled (a) represents an exothermic reaction while the line labeled (b) represents an endothermic reaction.
(2) the line labeled (a) represents an endothermic reaction while the line labeled (b) represents an exothermic reaction.
(3) The lines represent no known physical reality since the equilibrium constant is independent of temperature.

22. Jack fused pyrolusite (MnO2) with potassium hydroxide pellets (KOH) which resulted in an internal oxidation-reduction reaction for which we may properly write the oxidation half-cell reaction as follows:

(1) 2 H2O + MnO2 <=> Mn+6 + 2e- + 4 OH-
(2) 2e- + 2 H2O + MnO2 <=> Mn+2 + 4 OH-
(3) 4 OH- + MnO2 <=> MnO42- + 2e- + 2 H2O
(4) 2 MnO2 <=> 2 MnO + O2
(5) MnO2 <=> Mn+2 + 2e- + O2

23. Two half-cells are coupled to each other in a typical arrangement involving two separated chambers, a salt bridge and a potentiometer in the external circuit. For the following cell

Ag(s)|Ag+(1M)||Ag+(.01M)|Ag(s)
the potential is..........
(1) the cell potential is -0.12V
(2) the cell potential is -0.06V
(3) the cell potential is 0.00
(4) the cell potential is +0.06V
(5) the cell potential is +0.12V

24. When n moles of an ideal gas expand isothermally from V to 2V, the entropy change for the expansion is........

(1) nRTln2
(2) -nRTln2
(3) nRln2
(4) -nRln2
(5) zero

25. Coupling the following two half reactions into a "galvanic" cell leads to a standard cell potential (DE°)that is..........

F2 + 2e- <=>2 F-      E° = +2.87
Li+ + e- <=>Li      E° = -3.05
(1) +8.97V
(2) + 5.92V
(3) +0.18V
(4) -5.92V
(5) -8.97V