CHEM 102 Winter 12 Exam 2 (A) Questions and Answers,100% CORRECT

CHEM 102 Winter 12 Exam 2 (A) Questions and Answers Potentially useful information: First order half-life: t1/2 = ln2 / k [A]t = - kt + [A]o ln[A]t = - kt + ln[A]o 1/[A]t = kt +1/[A]o 1. Please choose the letter “a” as your answer for this question. 2. Which choice is an example of an amorphous solid? a. NaCl b. graphite c. iron d. diamond e. glass 3. Which choice is an example of an ionic solid? a. NaCl b. diamond c. iron d. quartz e. glass 4. In body-centered cubic unit cells, of the atom in the center of the unit cell is counted as part of that unit cell. a. all b. none c. 1/2 d. 1/4 e. 1/8 5. Elements most likely to be used for doping silicon in making semiconductors are a. Ba, La, and Y. b. Ne, Ar, and Kr. c. Ga, As, and B. d. Au, Ag, and Cu. e. Li, Na, and K. 6. In an n-type doped semiconductor the charge carriers are the because . a. holes; electrons move to fill a hole, thus leaving a hole elsewhere b. holes; there are extra electrons that can move freely c. nuclei; they are not locked into one location d. electrons; there are extra electrons that move freely e. electrons; the doping atoms have fewer electrons 7. Which unit is appropriate for describing reaction rates? a. kJ mol-1 b. C min-1 c. M min-1 d. kJ g-1 e. g L-1 8. The rate of the chemical reaction involving two substances, A and B, is measured. It is found that if the initial concentration of A used is doubled, keeping the B concentration the same, the rate doubles. If the concentrations of both A and B are doubled, the rate is eight times that measured in the first experiment. The rate law for this reaction is rate = a. k[A][B]. b. k[A]2[B]. c. k[A][B] 2. d. 2k[A][B]. e. k[A][B]/2. 9. Consider the reaction NO2 + O3  NO3 + O2 Use the data shown to determine the rate law for the reaction. Experiment [NO2] (M) [O3] (M) Rate (M s-1) 1 0.21 0.70 6.30  10-3 2 0.63 0.70 1.89  10-2 3 0.21 0.35 3.15  10-3 4 0.42 0.35 6.30  10-3 a. rate = k[NO2] [O3] b. rate = k[NO2]2 [O3] c. rate = k[NO2] [O3] 2 d. rate = k[NO2] e. rate = k[NO3] [O3]/ [NO2] [O2] 10. The rate law for a given reaction is rate = k [reactant]2, with k = 2.64  10-4 M-1 min-1. If the initial concentration is 0.0250 M, what is the initial rate, with the correct units? a. 4.36  10-11 M min-1 b. 1.65  10-7 min-1 c. 6.60  10-6 M min-1 d. 1.65  10-7 M min-1 e. 6.60  10-6 min-1 11. Which of the following statements is true about the rate of a reaction when the temperature is increased? a. The rate increases because the mechanism changes. b. The rate increases because the molecules have more energy. c. The rate decreases because the molecules are further apart. d. The rate decreases because the activation energy increases. e. The rate stays constant because reaction rate is independent of temperature. 12. If the rate law for the reaction 2A + 3B  products is first order in A and second order in B, then the rate law is , and the overall order is . a. k[A][B]; 2 b. k[A]2[B]3; 3 c. k[A][B]2; 3 d. k[A]2[B]; 3 e. k[A]2[B]2; 2 13. If the rate law for an elementary reaction is second order, we can conclude that a. no catalysts are involved in the reaction. b. intermediates are formed in the reaction. c. additional experiments at different temperatures are needed to determine the molecularity of the reaction. d. the elementary reaction involves a collision between two molecules. e. the elementary reaction is unimolecular. 14. The mechanism for formation of the products C and X is: A + B  C + D (slow) B + D  X (fast) The rate-limiting step in this reaction is Step , because . a. 1; the first step is always the rate-limiting step b. 2; the last step is always the rate-limiting step c. 1; it is the slow step d. 2; it is the fast step e. 2; it contains the product 15. Which of the following factors increases the rate of a chemical reaction by decreasing the activation energy barrier? a. increasing the temperature b. decreasing the temperature c. adding a catalyst d. increasing the surface area of reactants e. increasing the concentration of reactants 16. The half-life for the first-order conversion of A to B is 2.22 hr. What is the rate constant? a. 0.312 hr-1 b. 0.465 hr-1 c. 1.54 hr-1 d. 2.22 hr-1 e. 3.20 hr-1 17. A reaction displays first-order kinetics. It therefore follows that a plot of versus time is linear, and that the slope of this plot = . a. [reactant]; -k b. [reactant]; k c. 1/[reactant]; -k d. 1/[reactant]; k e. ln[reactant]; -k 18. Terms relating to certain types of substances are conventionally omitted from equilibrium constant expressions. These substances are a. pure liquids and gases. b. pure solids and liquids. c. pure solids only. d. pure liquids only. e. pure solids, liquids and gases. 19. The equilibrium constant expression for the reaction given below is 4 NH3(g) + 5 O2(g) 4 NO(g) + 6 H2O(g) a. b. c. d. e. 20. Consider the equilibrium reaction 2 NO2(g) N2O4(g) . A sample of pure NO2(g) of concentration 0.140 M is allowed to come to equilibrium. It is then found that 57.0 % of the NO2(g) has reacted to form N2O4(g). What is the value of Kc? a. 0.21 b. 0.38 c. 0.75 d. 4.7 e. 11 21. Consider the reaction H2(g) + Br2 (g) 2 HBr(g) . If the partial pressures in an equilibrium mixture of H2, Br2, and HBr are 0.024 atm, 0.031 atm, and 5.07 atm, respectively, the value of Kp for this reaction at this temperature is a. 3.5  104. b. 1.4  104. c. 6.8  103. d. 3.7  102. e. 1.9  102. 22. The equilibrium constant for the reaction NO(g) + 1/2 O2(g) NO2(g) has a value of Kc = 1.23 at a certain temperature. What is the value of Kc for the reaction 2 NO2(g) 2 NO(g) + O2(g) a. 2.46 b. 1.51 c. 0.66 d. 0.41 e. -1.51 23. Consider the reaction COCl2 (g) CO(g) + Cl2 (g) At equilibrium, [CO] = 4.14  10-6 M; [Cl2] = 4.14  10-6 M; and [COCl2] = 0.0627 M. Calculate the value of the equilibrium constant, Kc. a. 2.73  10-10 b. 6.60  10-5 c. 1.32  10-4 d. 1.51  104 e. 3.66  109 24. The value of Kc for the reaction A B is 6.3  1011. At equilibrium a. The amount of A is slightly less than the amount of B. b. The amount of A is much larger than the amount of B. c. The amount of A is much less than the amount of B. d. The amount of A is very close to the amount of B. e. More information is needed to make any statement about the relative amounts of A and B. 25. For the reaction 2A B Kc = 1.4  1015. In an equilibrium mixture, [A] = 0.45 M. What is the concentration of B? a. 2.8  1014 b. 0.90 c. 1.1  1015 d. 6.3  1014 e. 2.5  107 chem102w12exam2a Answer Section MULTIPLE CHOICE 1. ANS: A PTS: 0 2. ANS: E PTS: 1 3. ANS: A PTS: 1 4. ANS: A PTS: 1 5. ANS: C PTS: 1 6. ANS: D PTS: 1 7. ANS: C PTS: 1 8. ANS: C PTS: 1 9. ANS: A PTS: 1 10. ANS: D PTS: 1 11. ANS: B PTS: 1 12. ANS: C PTS: 1 13. ANS: D PTS: 1 14. ANS: C PTS: 1 15. ANS: C PTS: 1 16. ANS: A PTS: 1 17. ANS: E PTS: 1 18. ANS: B PTS: 1 19. ANS: E PTS: 1 20. ANS: E PTS: 1 21. ANS: A PTS: 1 22. ANS: C PTS: 1 23. ANS: A PTS: 1 24. ANS: C PTS: 1 25. ANS: A PTS: 1