BCIT Winter Chem Exam #1

Transcription

1 BCIT Winter 2014 Chem 0012 Exam #1 Name: Attempt all questions in this exam. Read each question carefully and give a complete answer in the space provided. Part marks given for wrong answers with partially correct reasoning/calculations. Equations and constants are given below. Periodic table is attached at the back. Total points = 30 R = L atm mol -1 K -1 = J mol -1 K -1 ln ln PV = nrt The solution to the quadratic equation ax² + bx +c =0 is 4 2 Page 1 of 9

2 Section I: Multiple choice (15 points total, 1 point each) Choose the BEST answer to the following questions. 1. Which of the following is most likely to have the greatest reaction rate at room temperature? a. 2H 2 (g) + O 2 (g) 2H 2 O( ) b. 2Ag + (aq) + CrO 4 2 (aq) Ag 2 CrO 4 (s) c. Pb(s) + 2HCl(aq) PbCl 2 (aq) + H 2 (g) d. CH 4 (g) + 2O 2 (g) CO 2 (g) + 2H 2 O(g) 2. Consider the following reaction: Fe 2 O 3 (s) + 2Al(s) Al 2 O 3 (s) + 2Fe(s) If 0.50 mol of Fe is produced in 10.0 sec, what is the rate of consumption of Fe 2 O 3 in mol/s? a. 5.0x10 2 mol/s b. 2.5x10 2 mol/s c. 1.0x10 1 mol/s d. 5.0 mol/s 3. The activation energy can be described as the a. energy of motion b. energy of the activated complex c. energy difference between the reactants and products d. energy difference between the reactants and the activated complex 4. Which of the following best describes the E a of a fast reaction and the stability of its activated complex? E a Activated Complex a. small unstable b. small stable c. large unstable d. large stable Page 2 of 9

3 5. How do the kinetic energy and potential energy change as reactant particles collide with each other? Kinetic Energy Potential Energy a. increases increases b. increases decreases c. decreases increases d. decreases decreases 6. What effect does a catalyst have on a reaction? a. It changes the H of a reaction. b. It increases the kinetic energy of the reactants. c. It decreases the potential energy of the products. d. It provides a reaction mechanism with lower activation energy. 7. In which of the following will entropy and enthalpy factors favour the establishment of equilibrium? a. CaCO 3 (s) kj CaO(s) + CO 2 (g) b. Mg(s) + 2HCl(aq) MgCl 2 (aq) + H 2 (g) kj c. 2C(s) + 2H 2 (g) C 2 H 4 (g) H = kj d. 2C 2 H 6 (g) +7O 2 (g) 4CO 2 (g) + 6H 2 O(g) H = 1560 kj 8. Consider the following equilibrium: H 2 (g) + I 2 (g) 2HI(g) colourless purple colourless Which of the following would allow you to conclude that the system has reached equilibrium? a. the pressure remains constant b. the reaction rates become zero c. The colour intensity remains constant d. The system shifts completely to the right Page 3 of 9

4 9. Consider the following system at equilibrium: 2NO(g) + Cl 2 (g) 2NOCl(g) H = 77kJ In which direction will the equilibrium shift and what happens to the value of K eq when Cl 2 (g) is added to the system? Shift K eq a. Right increases b. Right stays constant c. Left stays constant d. Left decreases 10. Consider the following equilibrium: Fe 2 O 3 (s) + 3CO(g) 2Fe(s) + 3CO 2 (g) Identify the equilibrium constant expression. a. b. c. d. Page 4 of 9

5 11. Consider the following equilibrium: N 2 (g) + 2O 2 (g) 2NO 2 (g) Equal moles of N 2 and O 2 are added, under certain conditions, to a closed container. Which of the following describes the changes in the reverse reaction which occur as the system proceeds toward equilibrium? Rate of Reverse Reaction [NO 2 ] a. increases increases b. increases decreases c. decreases decreases d. decreases increases 12. Consider the following equilibrium: CH 3 COOH(aq) + H 2 O( ) CH 3 COO (aq) + H 3 O + (aq) + heat A stress was applied at time t 1 and the data was plotted on the following graph: The stress that was imposed at time t 1 is the result of a. the addition of HCl. b. decreasing the temperature. c. the addition of CH 3 COO d. increasing the volume of the container Page 5 of 9

6 13. Consider the following potential energy diagram for an equilibrium system: When the temperature of the system is increased, the equilibrium shifts to the a. left and the K eq increases b. left and the K eq decreases c. right and the K eq increases d. right and the K eq decreases 14. A container is initially filed with pure SO 3. After a period of time, the following equilibrium is established: 2SO 2 (g) + O 2 (g) 2SO 3 (g) K eq = 7.0x10 25 What does this equilibrium mixture contain? a. mostly products b. mostly reactants c. 3 / 5 reactants and 2 / 5 products d. equal amounts of reactants and products 15. Consider the following equilibrium: 2CO(g) + O 2 (g) 2CO 2 (g) K eq = 4.0x10 10 What is the value of K eq for 2CO 2 (g) 2CO(g) + O 2 (g)? a. 4.0x10 10 b. 2.0x10 5 c. 5.0x10 4 d. 2.5x10 9 Page 6 of 9

7 Section II: Written problems (15 points total). 16. Consider the reaction: A(aq) + B(aq) C(aq) a. From the following data obtained at 20 C temperature, determine the rate law and the rate constant. (5 points) [A] (M) [B] (M) Reaction Rate (M/s) Rate = k[a] x [B] y Rate = (0.080 M 1 s 1 )[A] 2 b. What is the reaction rate when [A] = 3.0 M and [B] = 2.0 M at 20 C? (1 point) Rate = k[a]² = = (0.080 M 1 s 1 )[3.0 M] 2 = 0.72 M s 1 Page 7 of 9

8 17. Use the potential energy diagram to answer the following: (3 points) a. What is the activation energy of the forward reaction? 30 kj b. What is H for the forward reaction? 20 kj c. Is the forward reaction endothermic or exothermic? _endothermic_ 18. Consider the following reaction mechanism : CH 3 OH(aq) + H + (aq) CH + 3 (aq) + H 2 O( ) CH + 3 (aq) + CH 3 COOH(aq) CH 3 COOHCH + 3 (aq) CH 3 COOHCH + 3 (aq) CH 3 COOCH 3 (aq)+ H + (aq) a. What is the catalyst in this mechanism? (1 point) H + b. What is the overall reaction? (1 point) CH 3 OH(aq) + CH 3 COOH(aq) CH 3 COOCH 3 (aq) + H 2 O( ) 19. Given: CO(g) + H 2 O(g) CO 2 (g) + H 2 (g) K 1 = 1.4 at 1000 K CO(g) + 3H 2 (g) CH 4 (g) + H 2 O(g) K 2 = 190 at 1000 K a. At 1000 K, what is the numerical value of K for the equilibrium? (2 points) 3CO(g) + 3H 2 O(g) 3CO 2 (g) + 3H 2 (g) Eq = 3 x Eq1 K = (K 1 )³ = (1.4)³ = 2.7 b. At 1000 K, what is the numerical value of K for the equilibrium? (2 points) CH 4 (g)+ 2H 2 O(g) CO 2 (g) + 4H 2 (g) Eq = Eq1 Eq Page 8 of 9

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