Chem 1412 Exam The compound RX 3. decomposes according to the equation R + R 2 + 3X 2 3RX 3 X 3

Transcription

1 Chem 1412 Exam 2 Student: 1. The compound RX 3 decomposes according to the equation 3RX 3 R + R 2 X 3 + 3X 2 In an experiment the following data were collected for the decomposition at 100 C. What is the average rate of reaction over the entire experiment? t(s)[rx 3 ](mol L -1 ) A mol L -1 s -1 B mol L -1 s -1 C mol L -1 s -1 D mol L -1 s -1 E mol L -1 s Consider the reaction 2NH 3 N 2 + 3H 2 If the rate [H 2 ]/ t is mol L -1 s -1, then [N 2 ]/ t is A mol L -1 s -1 B mol L -1 s -1 C mol L -1 s -1 D mol L -1 s -1 E mol L -1 s -1 1

2 3. For the reaction 2A + B + 2C D + E the following initial rate data was collected at constant temperature. Determine the correct rate law for this reaction. All units are arbitrary. Trial [A] [B] [C] Rate A.Rate = k [A][B][C] B.Rate = k [A] 2 [B][C] C.Rate = k [A] 2 [B][C] -1 D.Rate = k [A][B] 2 [C] -1 E.none of these choices is correct 4. When the reaction A B + C is studied, a plot of ln[a] t vs. time gives a straight line with a negative slope. What is the order of the reaction? A.zero B.first C.second D.third E.More information is needed to determine the order. 5. Which one of the following sets of units is appropriate for a second-order rate constant? A.s -1 B.mol L -1 s -1 C.L mol -1 s -1 D.mol 2 L -2 s -1 E.L 2 mol -2 s -1 2

3 6. Ammonium cyanate (NH 4 CNO) reacts to form urea (NH 2 CONH 2 ). At 65 C the rate constant, k, is 3.60 s -1. What is the rate law for this reaction? A.Rate = 3.60 s -1 [NH 4 CNO] B.Rate = 3.60 s -1 [NH 4 CNO] 2 C.Rate = 0.28 s -1 [NH 4 CNO] D.Rate = 0.28 s -1 [NH 4 CNO] 2 E.Rate = 3.60 s -1 [NH 2 CONH 2 ] Sucrose decomposes to fructose and glucose in acid solution. When ln [sucrose] is plotted vs. time, a straight line with slope of hr -1 results. What is the rate law for the reaction? A.Rate = hr -1 [sucrose] 2 B.Rate = hr -1 [sucrose] C.Rate = hr [sucrose] 2 D.Rate = hr [sucrose] E.Rate = mol L -1 hr -1 [sucrose] 0 8. The decomposition of hydrogen peroxide is a first-order process with a rate constant of min - 1. How long will it take for the concentration of H 2 O 2 to drop from M to M? A.< 1 min B.7.55 min C.481 min D.4810 min E.2,654 min 9. The rate law for the rearrangement of CH 3 NC to CH 3 CN at 800 K is rate = (1300 s -1 )[CH 3 NC]. What is the half-life for this reaction? A s B s C s D.520 s E.1920 s 3

4 10. The rate law for the reaction 3A C is Rate = L mol -1 hr -1 [A] 2 What is the half-life for the reaction if the initial concentration of A is M? A hr B hr C.15.9 hr D.23.9 hr E.91.7 hr 11. A reactant R is being consumed in a first-order reaction. What fraction of the initial R remains in 4.00 half-lives? A B C D E The radioactive isotope tritium decays with a first-order rate constant k of year -1. What fraction of the tritium initially in a sample is still present 30 years later? A.0.19 B.0.60 C.0.15 D E.none of these choices is correct 13. If the activation energy of a reaction increases by 10.0 kj/mol, from 90.0 to kj/mol, what effect will this have on the rate of reaction at 298K? A.The rate will increase, by a factor of more than 50. B.The rate will decrease, by a factor of more than 50. C.The rate will increase, by a factor of less than 50. D.The rate will decrease, by a factor of less than 50. E.The rate will not change unless temperature changes. 4

5 14. The decomposition of dinitrogen pentaoxide to nitrogen dioxide and oxygen follows first-order kinetics and has an activation energy of 102 kj/mol. By what factor will the fraction of collisions with energy greater than or equal to the activation energy increase if the reaction temperature goes from 30 C to 60 C? A.1.00 B.1.10 C.2.00 D.4.00 E A catalyst accelerates a reaction because A.it increases the number of molecules with energy equal to or greater than the activation energy. B.it lowers the activation energy for the reaction. C.it increases the number of collisions between molecules. D.it increases the temperature of the molecules in the reaction. E.it supplies energy to reactant molecules. 16. When a chemical system is at equilibrium, A.the concentrations of the reactants are equal to the concentrations of the products. B.the concentrations of the reactants and products have reached constant values. C.the forward and reverse reactions have stopped. D.the reaction quotient, Q, has reached a maximum. E.the reaction quotient, Q, has reached a minimum. 17. The reaction quotient for a gas phase reaction has a value of If the number of moles of reactants in the reaction equation is equal to that of the products, which of the following statements is true? A.The reaction must proceed to the left to establish equilibrium. B.The reaction must proceed to the right to establish equilibrium. C.When the system is at equilibrium, the concentrations of the products will be much larger than the concentrations of the reactants. D.The concentrations of the products are generally larger than the concentrations of the reactants. E.None of these statements is true. 5

6 18. Write the mass-action expression, Q c, for the following chemical reaction. 3ClO 2 - (aq) 2ClO3 - (aq) + Cl - (aq) A. B. C. D. E. 19. What is the mass-action expression, Q c, for the following chemical reaction? PbO(s) + CO Pb(l) + CO 2 A. B. C. D. E.None of these expressions is correct. 6

7 20. Hydrogen sulfide will react with water as shown in the following reactions. H 2 S + H 2 O(l) H 3 O + (aq) + HS - (aq); K 1 = HS - (aq) + H 2 O(l) H 3 O + (aq) + S 2- (aq); K 2 =? H 2 S + 2H 2 O(l) 2H 3 O + (aq) + S 2- (aq); K 3 = What is the value of K 2? A B C D E Consider the following two equilibria and their respective equilibrium constants: (1) NO + ½O 2 NO 2 (2) 2NO 2 2NO + O 2 Which one of the following is the correct relationship between the equilibrium constants K 1 and K 2? A.K 2 = 2/K 1 B.K 2 = (1/K 1 ) 2 C.K 2 = -K 1 /2 D.K 2 = 1/(2K 1 ) E.K 2 = 1/(2K 1 ) The reaction of nitrogen with oxygen to form nitrogen monxide can be represented by the following equation. N 2 + O 2 2NO At 2000 C, the equilibrium constant, K p, has a value of What is the value of K c? A B C D.7.75 E.none of these choices is correct 7

8 23. Compounds A, B, and C react according to the following equation. 3A + 2B 2C At 100 C a mixture of these gases at equilibrium showed that [A] = 1.87 M, [B] = 1.23 M, and [C] = M. What is the value of K c for this reaction? A B C.1.66 D.3.24 E.> The equilibrium constant K c for the reaction PCl 3 + Cl 2 PCl 5 is 49 at 230 C. If 0.70 mol of PCl 3 is added to 0.70 mol of Cl 2 in a 1.00-L reaction vessel at 230 C, what is the concentration of PCl 3 when equilibrium has been established? A M B.0.11 M C.0.30 M D.0.59 M E.0.83 M 25. At a certain temperature the reaction CO 2 + H 2 CO + H 2 O has K c = If 2.00 mol of carbon dioxide and 1.5 mol of hydrogen are placed in a 5.00 L vessel and equilibrium is established, what will be the concentration of carbon monoxide? A M B M C M D M E.1.05 M 8

9 26. The reaction system POCl 3 POCl + Cl 2 is at equilibrium. Which of the following statements describes the behavior of the system if the partial pressure of chlorine is increased by 50%? A.POCl 3 will be consumed as equilibrium is established. B.POCl will be consumed as equilibrium is established. C.Chlorine will be produced as equilibrium is established. D.The partial pressure of POCl will decrease while the partial pressure of Cl 2 increases as equilibrium is established. E.The volume will have to decrease before equilibrium can be reestablished. 27. Methanol can be synthesized by combining carbon monoxide and hydrogen. CO + 2H 2 CH 3 OH A reaction vessel contains the three gases at equilibrium with a total pressure of 1.00 atm. What will happen to the partial pressure of hydrogen if enough argon is added to raise the total pressure to 1.4 atm? A.The partial pressure of hydrogen will decrease. B.The partial pressure of hydrogen will increase. C.The partial pressure of hydrogen will be unchanged. D.K p needs to be known before a prediction can be made. E.Both K p and the temperature need to be known before a prediction can be made. 28. Methanol can be synthesized by combining carbon monoxide and hydrogen. CO + 2H 2 CH 3 OH; H rxn = kj A reaction vessel contains these compounds at equilibrium. What effect will be seen when equilibrium is re-established after decreasing the temperature by 45 C? A.All the partial pressures will decrease. B.The partial pressure of methanol will decrease. C.The partial pressures of hydrogen and methanol will decrease. D.The partial pressure of hydrogen will increase. E.The partial pressure of carbon monoxide will decrease. 9

10 29. The following reaction is at equilibrium at a pressure of 1 atm, in a closed container. NaOH(s) + CO 2 NaHCO 3 (s); H rxn < 0 Which, if any, of the following actions will decrease the concentration of CO 2 gas present at equilibrium? A.adding N 2 gas to double the pressure B.adding more solid NaOH C.increasing the volume of the container D.lowering the temperature E.none of these choices is correct 30. Hydrogen sulfide can be formed in the following reaction: H 2 + ½S 2 H 2 S; H rxn = -92 kj The equilibrium constant K p = 106 at 1023 K. Estimate the value of K p at 1218 K. A.5.05 B.18.8 C.34.7 D.88.9 E

11 Chem 1412 Exam 2 Key 1. (p. 676) D 2. (p. 678) D 3. (p. 685) D 4. (p. 688) B 5. (p. 686) C 6. (p. 686) A 7. (p. 688) B 8. (p. 690) E 9. (p. 690) B 10. (p. 691) B 11. (p. 690) E 12. (p. 690) A 13. (p. 693) B 14. (p. 695) E 15. (p. 706) B 16. (p. 724) B 17. (p. 727) D 18. (p. 729) A 19. (p. 732) A 20. (p. 729) C 21. (p. 731) B 22. (p. 734) B 23. (p. 738) D 1

12 24. (p. 739) B 25. (p. 739) A 26. (p. 746) B 27. (p. 746) C 28. (p. 750) E 29. (p. Sec. 17.6) D 30. (p. 751) B 2

13 Chem 1412 Exam 2 Summary Category # of Questions Difficulty: E 8 Difficulty: H 9 Difficulty: M 13 Silberberg Kinetics Silberberg Equilibrium