CHE 107 21 November 1996
Mid-Term Examination III
University of Kentucky Department of Chemistry
Mid-Term Examination III
University of Kentucky Department of Chemistry1. Consider the reaction
If H2 is being consumed at the rate of 0.60 M/s, at what rate is NH3 being formed?
A. 0.20 M/s B. 0.40 M/s C. 0.60 M/s D. 0.90 M/s
2. Nitrosyl chloride, NOCl, is formed according to the balanced reaction
Which is the correct rate law for this reaction?
A. - delta [NO]/ 2 delta t = k [NO]2 [Cl2] B. - 2 delta [NO]/ delta t = k [NO]2 [Cl2] C. - delta [NO]/ 2 delta t = 2 k [NO] [Cl2] D. Experimental data are needed to determine this rate law.
3. What is the rate law for the reaction
as determined from the data below?
| [H2PO2-], M | [OH-], M | Initial rate, M/min |
|---|---|---|
| 0.10 | 1.0 | 3.2 × 10-5 |
| 0.30 | 1.0 | 1.0 × 10-4 |
| 0.10 | 2.0 | 1.3 × 10-4 |
A. rate = k[H2PO2-] B. rate = k[H2PO2-][OH-]4 C. rate = k[H2PO2-]2[OH-] D. rate = k[H2PO2-][OH-]2
4. If a reaction rate law is first order in both [A] and [B], what is the effect of halving [A] and tripling [B]?
A. The reaction rate is unchanged. B. The reaction rate is increased by a factor of 1.5. C. The reaction rate is multiplied by a factor of 6. D. The reaction rate is decreased by a factor of 1.5 (i.e., multiplied by 2/3).
5. The rate constant for the first–order reaction
is 2.2 × 10-5 s-1 at 320oC. If 8.00 g SO2Cl2 are heated to 320oC for 10.0 hrs, how many grams of SO2Cl2 are left unreacted?
A. 7.9 g B. 3.6 g C. 2.2 g D. 0.81 g
6. Formic acid decomposes at 550oC by the reaction:
A. 12 min B. 23 min C. 35 min D. 48 min
7. Use the plot below to estimate the rate of the reaction at time = 30 s.
A. rate = 0.01 M s-1 B. rate = 0.6 M s-1 C. rate = 0.1 M s-1 D. The rate cannot be determined without knowing the rate law for the reaction.
8. The N2O4/NO2 system is described by the elementary reactions
k2 N2O4(g) ---> 2 NO2(g)
What is the equilibrium constant for the reaction
A. Keq = k1 / k2 B. Keq = k2 / k1 C. Keq = k12 / k2 D. Keq = (k2 / k1)2
9. What is the activation energy for the reaction, A + B ---> C + D ?
A. 20 kJ/mol B. 5 kJ/mol C. 10 kJ/mol D. 15 kJ/mol
10. The second-order rate constant for the reaction
is 0.498 M/s at 592 K and 4.74 M/s at 656 K. What is the activation energy of the reaction?
A. 114 kJ/mol B. 57.5 kJ/mol C. 14.7 kJ/mol D. 300 J/mol
11. Ozone is destroyed in the upper atmosphere by this series of elementary reactions. Step 1 is the slower step. All species are in the gas phase.
k2 O + ClO ---> O2 + Cl
Which statement is correct?
A. O2 is an intermediate in this reaction sequence. B. The net reaction of this sequence is 2 O3 = 3 O2 C. Cl catalyzes the reaction of O3 with O. D. The concentration [Cl] will have an exponent of zero in the rate law for the net reaction of this sequence.
| Reaction | Eo (V) |
|---|---|
| Na+(s) + e- ---> Na(s) | -2.71 |
| Al3+(aq) + 3 e- ---> Al(s) | -1.66 |
| Zn2+(aq) + 2 e- ---> Zn(s) | -0.76 |
| Ni2+(aq) + 2 e- ---> Ni(s) | -0.25 |
| Pb2+(aq) + e- ---> Pb(s) | -0.13 |
| Ag+(aq) + e- ---> Ag(s) | 0.80 |
| Br2(g) + 2 e- ---> 2 Br-(aq) | 1.07 |
| O2(g) + 4 H+(aq) + 4 e- ---> 2 H2O(l) | 1.23 |
| Cl2(g) + 2 e- ---> 2 Cl-(aq) | 1.36 |
12. Which oxidation state is correctly assigned?
A. N has an oxidation state of +1 in NH4+. B. S has an oxidation state of +1 in SO32-. C. Na has an oxidation state of +1 in sodium metal. D. Cl has an oxidation state of +1 in ClO-.
13. Balance, with the minimum integers, this reaction describing the tarnishing of a silver spoon in contact with an egg yolk:
a b c d e A. 2 1 1 1 1 B. 4 2 1 2 2 C. 8 4 1 2 2 D. 4 1 1 2 1
14. A 0.80 g piece of Zn (65.4 g/mol) is placed in 100.0 mL of a 0.100 M solution of AgNO3(aq). How many grams of Zn metal remain after the reaction has gone to completion?
A. 0.00 g B. 0.15 g C. 0.47 g D. 0.65 g
15. Which of these species is the strongest reducing agent? Use the table of standard reduction potentials above.
A. Cl2(g) B. Cl-(aq) C. Pb2+(aq) D. Pb(s)
16. What is Eo for a voltaic cell based on the reaction
A. 1.41 V B. 1.91 V C. 2.57 V D. 4.48 V
17. In which of the following are the qualitative relationships between delta Go, Eo, and Keq correct?
delta Go Eo Keq A. >0 <0 >1 B. <0 <0 <1 C. >0 >0 >1 D. <0 >0 >1
18. What is the potential of the half-cell shown below in pure (neutral) water with p(O2) = 0.10 atm at 298 K? [Hint: RT/F = 0.0257 V at 298 K and 2.303 RT/F = 0.0591 V at 298 K]
A. 0.24V B. 0.80V C. 1.23 V D. 1.66 V
19. Aluminum metal is produced by the Hall-Héroult process. The (idealized) net electrolysis reaction is
Which reaction occurs at the cathode during the electrolysis?
A. Al3+ + 3 e- ---> Al(l) B. 2 O2- + C (graphite) ---> CO2(g) + 4 e- C. Al(l) ---> Al3+ + 3 e- D. O2(g) + 4 e- ---> 2 O2-
20. An aqueous solution of a gold salt is electrolyzed by passing a current of 0.250 A for 2.00 hrs. As a result, 1.23 g of metallic gold is formed at the cathode. What is the charge on the Au ions in the solution?
A. +1 B. +2 C. +3 D. +4
21. Most metals are found in nature
A. as the free, elemental metals. B. as ores, in the metals' positive oxidation states. C. as ores, in the metals' negative oxidation states. D. as part of the earth's atmosphere.
22. Three of the following reactions take place during roasting processes. Which one does not?
A. CaCO3(s) ---> CaO(s) + CO2(g) B. 2 Al(OH)3(s) ---> Al2O3(s) + 3 H2O(g) C. CuO(s) + H2(g) ---> Cu(s) + H2O(g) D. 2 PbS(s) + 3 O2(g) ---> 2 PbO(s) + 2 SO2(g)
23. Which metal is correctly matched with its maximum oxidation state?
A. Mn, 7+ B. Cr, 5+ C. Sc, 5+ D. Os, 10+
24. In which of these pairs is the first atom or ion significantly (at least 15%) larger than the second atom or ion?
A. Fe3+, Fe2+ B. Os, Ru C. Sc, Fe D. Yb, Ce
25. Which reaction is not used commercially to reduce a metal ore to the metal?
A. HgS(s) + O2(g) ---> Hg(l) + SO2(g) electrolysis B. 2 NaCl(l) ---------> 2 Na(l) + Cl2(g) C. Au2O(s) + C(s) ---> 2 Au(l) + CO(g) D. 2 Fe2O3(s) + 6 C(s) + 3 O2(g) ---> 4 Fe(l) + 6 CO2(g)