pts) 1.
(6 In the following reaction 2 MnO4-(aq) + 5 H2O2(R) + 6H+(aq) 6 2 Mn2+(aq) + 8 H2O(R) + 5 O2(g) the concentration of MnO4- dropped from 0.5684 M to 0.5522 M in 2.23 minutes. What was the average rate of formation of O2, in M/min, during this time interval? a) 2.14 x 10-3 b) 1.82 x 10-2 c) 2.09 x 10-2 d) 6.37 x 10-2 e) 8.50 x 10-1
2.
(5 pts) Concentration and time data is obtained for a reaction. Which of the following statements is incorrect about the reaction? a) If Rn[A]t is plotted against time and the graph gives a straight line, the reaction was first order with respect to A. b) The half-life of a first order reaction is a constant. c) When 1/[A]t is graphed against time, the slope of the line is equal to the rate constant for a second order reaction. d) The half-life of a second order reaction decreases as the concentration of the reactants decrease. e) The rate of reaction at a specific time can be determined from the slope of the line tangent to the curve at that time on a graph of concentration versus time.
3.
(5 pts) The half-life of of U-235. a) 4.7 x 108 yr-1 b) 8.0 x 104 yr-1 c) 19 yr-1 d) 6.5 x 10-5 yr-1 e) 9.8 x 10-10 yr-1
, a naturally radioactive isotope is 7.1 x 108 years. Radioactive
235 92 U
decay is a first-order kinetic reaction. Calculate the rate constant for the radioactive decay
(1) The initial rate of a hypothetical reaction 3A + B 6 2C
was measured at different concentrations of A and B. The results are summarized below: Experiment Number 1 2 3 4 Initial Concentration [A] 1.20 M 0.40 M 1.20 M 0.72 M Initial Concentration [B] 0.50 M 0.50 M 1.00 M 0.48 M Initial Rate of Reaction M/s 1.08 x 10-1 1.2 x 10-2 1.08 x 10-1 ?
Questions 4 - 6 refer to this reaction.
4.
(6 pts) The rate law for the reaction is a) rate = k[A] b) rate = k[A][B]2 c) rate = k[A][B] d) rate = k [A]2[B] e) rate = k[A]2
5.
(5 pts) The numerical value of the rate constant for this reaction is a) 0.0750 b) 0.0905 c) 0.150 d) 0.384 e) 0.628
6.
(5 pts) The initial rate of the reaction for experiment 4 is a) 7.4 x 10-3 M/s b) 1.7 x 10-2 M/s c) 3.9 x 10-2 M/s d) 4.3 x 10-1 M/s e) 8.5 x 10-1 M/s (2)
7.
(6 pts) A reaction is second order in C. The rate constant is determined to be 2.35 x 10-3 M-1s-1. The reaction flask initially contains 0.530 M of C. How much C will remain after 12.0 minutes?
a) 0.360 M b) 0.279 M c) 0.182 M d) 0.149 M e) 0.114 M 8. (5 pts) The rate constant of a reaction which is first order in A is 7.8 x 10-2 s-1. What is the initial rate of the reaction when the initial concentration of A is 0.0030 M? a) 2.3 x 10-4 M/s b) 7.9 x 10-4 M/s c) 9.1 x 10-4 M/s d) 2.6 x 101 M/s e) 8.5 x 101 M/s 9. (6 pts) A reaction is first order with respect to A. The concentration of A was initially 3.50 M and after 764 seconds [A] = 0.826 M. Calculate the concentration of [A] after 1080 seconds. a) 0.810 M b) 0.703 M c) 0.614 M d) 0.455 M e) 0.381 M 10. (5 pts) The reaction of A is a second order reaction. 10.0 g of A is placed in container I while 50.0 g of A is placed in container II. Both containers are kept at the same temperature and pressure. The rate constant for the reaction is 7.6 x 10-2 M-1s-1. Compare the time required for half of A to decompose in each container.
I II a) Container I requires the same amount of time as container II. b) Container II requires five times as much time as container I. c) Container I requires five times as much time as container II. d) Select this answer if the correct answer is not given above. 11. (3) (6 pts) A reaction obeys the rate law expression: Rate = k[B][C]2 at 47.3C. The rate constant was determined to be 2.8 x 10-3 M-2s-1 at that temperature. The activation energy for the reaction
is 95.0 kJ/mole. Calculate the rate constant at 61.9C. a) 8.7 x 10-3 M-2s-1 b) 7.2 x 10-2 M-2s-1 c) 1.3 x 10-2 M-2s-1 d) 9.9 x 10-2 M-2s-1 e) 1.8 x 10-1 M-2s-1
12.
(6 pts) Examine the following potential energy diagrams of two reactions.
Which of the following statements is incorrect? a) The forward reaction of Reaction 1 has a smaller rate constant than the forward reaction of Reaction 2. b) The activation energy of Reaction 1 in the forward direction is greater than the activation energy of the reverse direction of Reaction 2. c) The rate of the forward reaction of Reaction 1 is greater than the rate of the reverse reaction of Reaction 1. d) The activated complex for the forward reaction of Reaction 2 is the same as the activated complex for the reverse reaction of Reaction 2. e) Ea for the reverse reaction of Reaction 1 is 93 kJ/mole. (4) The following mechanism is proposed for a reaction.
Step 1: Step 2: Step 3:
Br2(g) Br(g) +
2 Br(g)
kf kr
fast, equilibrium CHBr3(g) k2 HBr(g) + CBr3(g) slow fast
Br(g) + CBr3(g)
CBr4(g)
k3
Questions 13 and 14 refer to this reaction and mechanism. 13. (5 pts) Which of the following statements is incorrect about the reaction or mechanism above? a) The rate determining step is a bimolecular elementary step. b) The balanced equation for the reaction is Br2(g) + CHBr3(g) 6 HBr(g) + CBr4(g). c) Br(g) and CBr3(g) are intermediates. The d) forward reaction of step 1 is a unimolecular reaction. e) k2 is greater than k3.
14.
(6 pts) The rate law predicted by the mechanism is a) rate = k[Br2]1/2[CHBr3] b) rate = k[Br2][CHBr3]2 c) rate = k[Br]2[CHBr3] d) rate = k[HBr][CBr4]/[Br]2 e) rate = k[2 Br]2/[CBr4]
15.
(5 pts) In the following mechanism B + AY2 BY + AY BY + AY 6 BY2 + A A + Y2 6 AY + Y AY + Y 6 AY2 fast slow fast fast
____________ is an intermediate and ___________ is a catalyst. a) AY, B b) Y2, BY c) BY, A d) Y, AY2 e) BY2, AY 16. (6 pts) Which of the following mechanisms is an acceptable mechanism for the reaction O3(g) + NO(g) 6 NO2(g) + O2(g)
(5)
which was determined to be first order with respect to both O3 and to NO? a) O3 6 O2 + O O + NO 6 NO2 b) NO 6 N + O O + O3 6 2 O2 O2 + N 6 NO2 c) 2 O2 + NO 6 NO2 + O3 2 O3 6 3 O2 d) NO + O3 6 NO3 + O NO3 + O 6 NO2 + O2 e) NO N + O O + O3 6 2 O2 O2 + N 6 NO2 slow fast slow fast fast slow fast slow fast fast slow fast
17.
(6 pts) Hydrogen and nitrogen are placed in an empty 5.00 L vessel at 500C. When equilibrium is established, 3.01 mole of N2, 2.10 mole of H2 and 0.565 mole of NH3 is present. Calculate Kc for the reaction at 500C. N2(g) + 3 H2(g) 2 NH3(g)
a) 1.13 x 10-2 b) 0.286 c) 0.509 d) 17.2 e) 63.8
(6) 18. (5 pts) Which of the following reactions is not correctly paired with its equilibrium constant expression?
a) CO2(g) + H2(g) CO(g) + H2O(g) b) (AlF6)3-(aq) Al3+(aq) + 6 F-(aq) c) 2 BrF5(g) Br2(g) + 5 F2(g)
Kc = [CO][H2O] [CO2][H2] Kc = [Al3+][F-]6 [AlF63-] Kp = (PBr2)(PF2)5 (P BrF5)2 Kc = [Fe2S3] [Fe3+]2[S2-]3 Kp = (PCO2)2 (PCO)2(PO2)
d) 2 Fe3+(aq) + 3 S2-(aq) Fe2S3(s)
e) 2 CO(g) + O2(g) 2 CO2(g)
19.
(6 pts) A mixture of 0.100 moles of N2 and 0.150 mole of H2 is placed in a 1.00 L vessel. At equilibrium the concentration of [N2] = 0.070 M. Calculate Kc for the reaction at this temperature. N2(g) + 3 H2(g) 2 NH3(g) a) 4.80 x 10-6 b) 2.67 x 10-3 c) 2.38 x 102 d) 5.64 x 103 e) 1.99 x 104
20.
(6 pts) The value of Kc = 1.55 x 103 for the reaction at 17C 2 H2S(g) + 3 O2(g) 2 H2O(g) + 2 SO2(g) What is the value of Kp? a) 5.34 b) 65.1 c) 4.70 x 102 d) 8.12 x 103 e) 3.69 x 104
(7)
21.
(6 pts) At 1133 K, Kp = 4.32 x 10-3 for the reaction CO(g) + 3 H2(g) CH4(g) + H2O(g)
What can you conclude about a reaction flask containing PCO = 1.58 atm, PH2 = 1.70 atm, PCH4 = 0.736 atm, and PH2O = 0.142 atm? a) The system will react to form more CH4 and H2O. b) The system will react to form more CO and H2. c) The system is at equilibrium. d) It is impossible to predict which direction the reaction will move.
22.
(6 pts) A 10.0 L flask is filled with 5.00 moles each of H2 and I2 at 448C. Kc is equal to 50.5 at 448C for the reaction H2(g) + I2(g) 2 HI(g) What is the concentration of HI at equilibrium? a) 0.144 M b) 0.279 M c) 0.503 M d) 0.625 M e) 0.780 M
23.
(6 pts) Calculate the value of Kc for the decomposition of NH4Cl(s) at some temperature. Solid NH4Cl was placed in a 2.00 L flask and decomposed. At equilibrium the flask contained 0.175 moles of NH3. NH4Cl(s) NH3(g) + HCl(g) a) 1.61 x 10-2 b) 7.66 x 10-3 c) 5.07 x 10-4 d) 2.53 x 10-5 e) 8.41 x 10-6
(8) 24. (6 pts) Which of the following stresses will shift the equilibrium to form more products? K2PtCl4(aq) + 2 NH3(g) Pt(NH3)2Cl2(s) + 2 KCl(aq) a) remove some NH3 b) add KCl solution
)H<0
c) remove some Pt(NH3)2Cl2 d) cool the reaction e) decrease the pressure
25.
(6 pts) Which of the following systems favor reactant formation when both the temperature is lowered and the pressure is raised? A. B. C. D. 2 Cu(NO3)2(s) 2 CuO(s) + 4 NO2(g) + O2(g) Na2CO3(s) + SO2(g) + O2(g) Na2SO4(s) + CO2(g) 3 CuO(s) + 2 NH3(g) 3 Cu(s) + 3 H2O(g) + N2(g) N2O4(g) 2 NO2(g)
)H = +439 kJ )H = -350.2 kJ )H = -1099 kJ )H = +60.2 kJ
a) both A and D b) both B and C c) C only d) B only e) A only
26.
(5 pts) The strongest acid in the following system is ___________. H2PO4- + H2SO3 HSO3- + H3PO4 a) b) c) d) HSO3H3PO4 H2SO3 H2PO4statements is incorrect?
27.
(5 pts) Which of the following
a) The conjugate acid of SO32- is HSO3-. b) The stronger the base, the weaker its conjugate acid. c) In an acid-base system, the equilibrium lies to the side with the weaker acid and base. d) The conjugate base of tartaric acid, C10H18O6, is C10H17O6-1. e) The conjugate acid always has one less proton than its base. 28. (9) (6 pts) Calculate the pH of a solution made by dissolving 0.1155 g Ca(OH)2 (f. wt. = 74.09 amu) in enough water to make 500.0 mL of solution. a) 11.7949 b) 11.1762 c) 9.9088 d) 9.3464
e) 7.9665 29. (6 pts) The pH of a banana is 4.6. Calculate the hydroxide ion concentration. a) 8 x 10-6 M b) 5 x 10-7 M c) 2 x 10-8 M d) 7 x 10-9 M e) 4 x 10-10 M 30. (6 pts) Calculate the pH of a 0.136 M nicotinic acid, HC6H4O2N (mol. wt. = 123.111 amu). Ka for nicotinic acid is 1.4 x 10-5. a) 1.67 b) 2.86 c) 4.52 d) 6.26 e) 7.06
31.
(6 pts) Calculate Ka for uric acid, HC5H3O3N4 (mol. wt. = 168.112 amu). A 0.500 M solution of the acid has a pH of 3.06 at 25C. a) 1.5 x 10-6 b) 8.2 x 10-5 c) 2.0 x 10-5 d) 7.4 x 10-4 e) 1.3 x 10-4
(10)