CHE 107 4 April 1996
MID-TERM EXAMINATION III
University of Kentucky Department of Chemistry
1. Which of the following describes the relationship between the rates at which Cl2 is consumed and ClF3 is produced in the following reaction:Cl2(g) + 3 F2(g) ---> 2 ClF3(s) A. - delta [Cl2]/ delta t = delta [ClF3]/ delta t B. 2 [ - delta [Cl2]/ delta t] = delta [ClF3]/ delta t C. - delta [Cl2]/ delta t = 3 delta [ClF3]/ delta t] D. 1/2 [ - delta [Cl2]/ delta t] = delta [ClF3]/ delta t
2. The reaction, A + 2 B ---> products, has the rate law:
rate = k[A][B]3 When the concentration of B is doubled and the concentration of A is doubled, by what factor will the rate of reaction increase?
A. 4 B. 8 C. 16 D. 2
3. The rate constant for a reaction has the units L mol-1 s-1. The overall order of the reaction is:A. 2 B. 1 C. 0 D. impossible to determine
4. For the reaction, 2 A + B ---> C + D, the following data were obtained. What is the rate law for the reaction?[A] [B] Initial Rate 0.150 M 0.800 M 0.500 M/min 0.0750 M 0.800 M 0.125 M/min 0.150 M 0.400 M 0.354 M/min
A. rate = k[A]2[B]1/2 B. rate = k[A]2 C. rate = k[A][B] D. rate = k[B][A]1/2
5. Which of the following graphs will result in straight line plots with negative slopes?1. ln [A] vs t for first-order 2. 1/[A] vs t for second-order 3. ln k vs 1/T 4. [A] vs t for zero-order
A. 1 and 2 B. 1, 3 and 4 C. 2 D. 3 and 4
6. A certain decomposition is known to be zero-, first-, or second-order. Experiments show that the half-life is directly proportional to the initial concentration, so thatA. the decomposition is either zero- or second-order. B. the decomposition is definitely first-order. C. the decomposition is definitely zero-order. D. the decomposition is definitely second-order.
7. Gaseous N2O5 decomposes according to the equation
N2O5(s) ---> 2 NO2(s) + 1/2 O2(s) The experimental rate law is:
- delta [N2O5]/ delta t = k[N2O5] At a certain temperature, the rate constant is k = 5.0 x 10-4 s-1. How many seconds will it take for the concentration of N2O5 to decrease to one-tenth of its initial value?
A. 5.5 x 103 s B. 4.6 x 103 s C. 2.1 x 103 s D. 5.0 x 10-3 s
8. In a second order reaction, the reactant decreased in concentration from 0.514 M to 0.253 M in 119 s. How long will it take to decrease from 0.253 M to 0.097 M?A. 119. s. B. 161. s. C. 209. s. D. 377. s.
9. Identify the false statements.1. At a given temperature, all molecules have the same kinetic energy. 2. Temperature has little or no effect on the Arrhenius factor, A. 3. Product is not always obtained even when the collisional energy between two molecules is greater than the activation energy (Ea). 4. A bimolecular reaction is generally twice as fast as a unimolecular reaction.
A. 1 and 3 B. 2 and 3 C. 2 and 4 D. 1 and 4
10. The rate law for a reaction is found to be
rate = k[A][B] If the temperature is increased from 25oC to 75oC,
A. the reaction rate increases but the value of k does not. B. the reaction rate and value of k increase. C. the reaction rate and value of k decrease. D. the reaction rate stays the same and the value of k increases.
11. A reaction rate constant increases by a factor of 2.81 when the temperature is increased from 16oC to 34oC. Calculate the activation energy for this reaction.A. 37.6 kJ mol-1 B. 3.76 kJ mol-1 C. 42.3 kJ mol-1 D. 4.23 kJ mol-1
12. The reaction, H2(g) + 2 ICl(g) ---> I2(g) + 2 HCl(g), is found to be first-order in H2 and first-order in ICl. If the first step in the proposed mechanism for the reaction is
H2 + ICl ---> HI + HCl (slow) which of the following would be a plausible second step that would complete the mechanism?
A. 2 HI --> H2 + I2 (fast) B. ICl + H2 ---> HCl + HI (fast) C. 2 HCl ---> Cl2 + H2 (fast) D. ICl + HI ---> I2 + HCl (fast)
13. For the reaction:
2 NO(g) + H2(g) ---> N2O(g) + H2O(g) the following mechanism has been proposed:
Keq 1. NO(g) + NO(g) = N2O2(g)
k2 2. N2O2(g) + H2(g) ---> N2O(g) + H2O(g)
The observed rate law = k[NO]2[H2]. Assume the mechanism is correct. (a) Identify the slow step and (b) express the concentration of the intermediate in terms of reactant concentrations.
A. Step 1; Keq[NO]2 B. Step 2; Keq[NO]2 C. Step 2; Keq[N2O2]1/2 D. Step 1; Keq[N2O2]2
14. When the redox reaction
ClO2 + IO3- ---> Cl- + IO4- is balanced in basic solution, the coefficients of ClO2, IO3-, Cl-, and IO4- are, respectively,
A. 1, 3, 1, 3 B. 2, 5, 2, 5 C. 2, 4, 2, 2 D. 3, 4, 3, 4
15. Which of the following statements are true for the following reaction in acidic solution?
Sn2+ + Cr2O72- + H+ ---> Sn4+ + Cr3+ + H2O 1. Sn2+ is the oxidizing agent. 2. Sn2+ is oxidized to Sn4+ and Cr2O72- is reduced to Cr3+. 3. A total of six electrons is transferred from the anode to the cathode in the balanced equation. 4. The reduction of Sn2+ occurs at the anode.
A. 2 and 3 B. 1 and 4 C. 2 and 4 D. 1 and 3
16. What is Eocell for the following reaction?
Cl2(g) + H2O(l) ---> Cl-(aq) + O2(g) + H+(aq) Given: 2 e + Cl2(g) ---> 2 Cl-(aq) Eo = 1.36 V 4 e + 4 H+(aq) + O2(g) ---> 2 H2O(l) Eo = 1.23 VA. 2.59 V B. 0.13 V C. 1.49 V D. 3.95 V
17. The standard cell potential (Eo) for a galvanic cell depends on:1. variations in the concentrations of all reactants and products. 2. the number of electrons transferred in the overall cell reaction. 3. the half-reaction at the anode. 4. the half-reaction at the cathode.
A. 1 and 2 B. 2 and 3 C. 1 and 3 D. 3 and 4
18. Given these half-reactions and Eo values:AuBr4-(aq) + 3 e ---> Au(s) + 4 Br-(aq) Eo = -0.86 V Eu3+(aq) + e ---> Eu2+(aq) Eo = -0.43 V IO-(aq) + H2O(l) + 2 e ---> I-(aq) + 2 OH-(aq) Eo = 0.49 V Sn2+(aq) + 2 e ---> Sn(s) Eo = -0.14 V
What is the largest cell potential possible through a combination of any two of the above half-reactions?
A. 0.630 V B. 0.570 V C. 1.35 V D. 0.714 V
19. Rank the following species in order of increasing strength as oxidizing agents in acidic solution:
Cr2O72-, H2O2, and Cu2+ given: H2O2 + 2 H+ + 2 e ---> 2 H2O Eo = -0.776 V Cu2+ + 2 e ---> Cu Eo = +0.34 V Cr2O72- + 14 H+ + 6 e ---> 2 Cr3+ + 7 H2O Eo = +1.33 VA. Cu2+ < H2O2 < Cr2O72- B. Cr2O72- < H2O2 < Cu2+ C. H2O2 < Cu2+ < Cr2O72- D. Cu2+ < Cr2O72- < H2O2
20. For a certain oxidation-reduction reaction, Eo is negative. It follows thatA. delta Go is negative and Keq < 1. B. delta Go is negative and Keq > 1. C. delta Go is positive and Keq < 1. D. delta Go is positive and Keq > 1.
21. Calculate the reduction potential at 25oC of the reaction
2 H+ + 2 e ---> H2(g) with the pressure of H2(g) at 1.50 atm, and [H+] = 0.100 M.
A. -0.0643 V B. -0.0348 V C. 0.0000 V D. -0.148 V
22. The solubility product constant for Cu(IO3)2 is 7.40 x 10-8 at 298.15 K. The standard reduction potential of the Cu2+/Cu sample is 0.337 V. Calculate delta Go at 25oC for the half-reaction
Cu(IO3)2(s) + 2 e ---> Cu(s) + 2 IO3-(aq) A. -24.4 kJ B. +97.4 kJ C. -106. kJ D. +106. kJ
23. Given the balanced half-reactions at 25oCAgBr(s) + e ---> Ag(s) + Br-(aq) Eo = 0.0711 V Ag+(aq) + e ---> Ag(s) Eo = 0.7991 V
Compute delta Go and Ksp for AgBr(s) ---> Ag+(aq) + Br-(aq).
A. delta Go = 84.0 kJ Ksp = 1.95 x 10-5 B. delta Go = -84.0 kJ Ksp = 5.20 x 1014 C. delta Go = -70.2 kJ Ksp = 8.97 x 108 D. delta Go = 70.2 kJ Ksp = 4.95 x 10-13
24. How long will it take to produce 78 g of Al metal by the reduction of Al3+ in an electrolysis cell with a current of 2.0 A?A. 1.4 x 105 s B. 6.0 x 105 s C. 4.2 x 105 s D. 5 s
25. The coating of aluminum with a thin impervious layer of aluminum oxide by electrolysis is known asA. cathodizing. B. sacrificial protection. C. anodizing. D. galvanization.