Chem 102--Exam #2 Multiple Choice Identify the letter of the choice that best completes the statement or answers the question. 1. When water is measured in a plastic graduated cylinder, a reverse meniscus is observed because a. the hydrogen bonds between water molecules are greater than the attractions between the water molecules and the walls of the container. b. the viscosity of the water is greater than the viscosity of the plastic. c. surface tension of the water prevents it from "beading up" inside the container. d. the molecules of water are forced closer together because of London forces. e. the attractive forces between the water molecules and the walls of the container are greater than the attractive forces between the water molecules. 2. Volatility is the a. temperature at which the equilibrium vapor pressure of a liquid is exactly equal to the atmospheric pressure. b. odor of a substance. c. temperature at which a gas can be converted into a liquid at atmospheric pressure. d. tendency of molecules of a gas to move closer together when the pressure is increased. e. tendency of a liquid to vaporize. 3. The Clausius-Clapeyron equation is useful for calculating a. the enthalpy of vaporization. b. the heat capacity. c. the relative humidity. d. the unit cell identity. e. the band gap. 4. Which group includes only exothermic processes? a. freezing, vaporization, deposition b. freezing, condensation, deposition c. melting, condensation, deposition d. melting, evaporation, sublimation e. melting, condensation, sublimation 5. A positive slope for a region of a heating curve indicates that _ in that region. a. no energy is being absorbed by the system b. energy is being given off by the system, but it cannot be measured c. energy is being absorbed by the system and is being used for a phase change d. additional data is needed to explain this observation e. energy is being absorbed by the system and is being used to increase the temperature
6. The temperature at point b is the a. critical point. b. triple point. c. absolute freezing point. d. normal freezing point. e. normal boiling point. 7. The simplest explanation for the unusual properties of water in comparison to other compounds of similar structure and molar mass is a. hydrogen bonding. b. covalent bonding. c. trigonal pyramidal structure. d. London forces. e. its purity. 8. Which choice is an example of an amorphous solid? a. NaCl b. ionic solid c. iron d. quartz e. glass 9. Which choice is an example of a network solid? a. NaCl b. crystal c. iron d. quartz e. glass 10. Because graphite contains carbon atoms that are covalently bonded to three other carbon atoms in the same layer, it is classified as a(an) _ solid. a. planar network b. amorphous c. three-dimensional network d. metallic e. ionic
Exhibit 13-1 The following question(s) relate to the reaction between water and a complex ion of Co 2+ ; the rate varies with concentration as follows. (The rate has no dependence on [H 2 O].) Trial [Co 2+ complex], M Initial rate, M min -1 1 1.14 10-3 3.2 10-7 2 2.28 10-3 6.4 10-7 3 3.42 10-3 9.6 10-7 4 1.14 10-2 3.2 10-6 11. Refer to Exhibit 13-1. The rate law for the reaction is rate = a. k 2 [Co 2+ complex]. b. k[co 2+ complex]. c. 2k[Co 2+ complex]. d. k[co 2+ complex]/2. e. k[co 2+ complex] 2. 12. Refer to Exhibit 13-1. The value and units of the rate constant are: a. 3.6 10 3 M min -1. b. 2.8 10-4 M min -1. c. 3.6 10 3 min -1. d. 2.8 10-4 min -1. e. 3.6 10 3 M -1 min -1. 13. From the stoichiometry of the reaction 2 I - (aq) + H 2 O 2 (aq) + 2 H 3 O + (aq) I 2 (s) + 4 H 2 O(l) the rate law a. is predicted to be third-order overall. b. is predicted to be first-order in I 2 (s). c. is predicted to be first-order in all reactants. d. is predicted to be fifth-order overall. e. cannot be predicted. 14. 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 15. 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 16. If an elementary reaction is exothermic, then a. The activation energy for the forward reaction is smaller than that for the reverse reaction. b. The sum of activation energies gives the value of H for the reaction. c. The activation energy for the forward reaction is larger than that for the reverse reaction. d. The activation energy for the forward reaction is positive, and for the reverse reaction, negative. e. The activation energy for the forward reaction is negative, and for the reverse reaction, positive.
17. A reaction intermediate is a species which a. speeds up a reaction by lowering the activation energy. b. slows down a reaction by raising the activation energy. c. is always produced in the rate-determining step. d. is always produced in an early step and consumed in a later step. e. is always consumed in an early step and regenerated in a later step. 18. 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 a phase interface e. increasing the concentration of reactants Exhibit 13-2 For the following question(s), consider the following reaction mechanism: Step 1 2X + Y W + 2Z fast Step 2 W + Z W + U + V slow Step 3 V + Z 2 W + Y fast 19. Refer to Exhibit 13-2. The intermediates in this reaction are a. Z and V. b. X and Y. c. Y only. d. W and Y. e. There are no intermediates in this reaction. 20. Refer to Exhibit 13-2. The catalysts in this reaction are a. Z and V. b. X and Y. c. Y only. d. W and Y. e. There are no catalysts in this reaction. Short Answer 21. (10 points) Consider the reaction mechanism shown in Exhibit 13-2. Write the rate law for this reaction mechanism.
Numeric Response 22. (20 points) t-butyl chloride, (CH3) 3 CCl, has a normal boiling temperature of 350 K. The vapor pressure at 298 K is 101 Torr. Calculate the enthalpy of vaporization, H o vap for this substance. 23. (20 points) The rate coefficient for a reaction was measured at two temperatures with the following results: Temperature (K) k (cm 3 molec -1 s -1 ) 295 3.25 x 10-15 505 9.47 x 10-12 Determine the Arrhenius expression for this rate coefficient.
Chem 102--Exam #2 Answer Section MULTIPLE CHOICE 1. ANS: A OBJ: 11.1 The Liquid State 2. ANS: E OBJ: 11.2 Vapor Pressure 3. ANS: A OBJ: 11.2 Vapor Pressure 4. ANS: B OBJ: 11.3 Phase Changes: Solids, Liquids, and Gases 5. ANS: E OBJ: 11.3 Phase Changes: Solids, Liquids, and Gases 6. ANS: E OBJ: 11.3 Phase Changes: Solids, Liquids, and Gases 7. ANS: A OBJ: 11.4 Water: An Important Liquid with Unusual Properties 8. ANS: E OBJ: 11.5 Types of Solids 9. ANS: D OBJ: 11.5 Types of Solids 10. ANS: A OBJ: 11.11 Cement, Ceramics, and Glass 11. ANS: B OBJ: 13.2 Effect of Concentration on Reaction Rate 12. ANS: D OBJ: 13.2 Effect of Concentration on Reaction Rate 13. ANS: E OBJ: 13.3 Rate Law and Order of Reaction 14. ANS: E OBJ: 13.3 Rate Law and Order of Reaction 15. ANS: A OBJ: 13.3 Rate Law and Order of Reaction 16. ANS: A OBJ: 13.4 A Nanoscale View: Elementary Reactions 17. ANS: D OBJ: 13.7 Reaction Mechanisms 18. ANS: C OBJ: 13.8 Catalysts and Reaction Rate 19. ANS: A OBJ: 13.7 Reaction Mechanisms 20. ANS: C OBJ: 13.7 Reaction Mechanisms SHORT ANSWER 21. ANS: rate = K [W] [Z] NUMERIC RESPONSE 22. ANS: 33.63 kj/mol 23. ANS: k(t) = 7.14 x 10-7 exp{-47.1 kj mol -1 /RT}