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General Chemistry II ____
Practice Problems for Exam 2
1. NO reacts with chlorine in in a gas phase reaction to form nitrosyl nitrosyl chloride, NOCl. From the following following experimental data, determine the form of the equation that describes the relationship of reaction rate to initial concentrations of reactants. 2NO + Cl2 → 2NOCl Run 1 2 3
____
Initial [NO] 0.50 M 0.50 M 1.00 M 1.00 M 1.00 M 1.00 M
→ N2O(g)
Experiement 1 2 3 a. b. c. d. e.
____
Initial Rate of Formation of NOCl 1.14 M 1.14 M /hr /hr 9.12 M 9.12 M /hr /hr 4.56 M 4.56 M /hr /hr
a. rate = k [NO] [NO] b. rate = k [NO][Cl [NO][Cl2] c. rate = k [NO] [NO]2 d. rate = k [NO] [NO]2[Cl2] e. rate = k [NO] [NO]2[Cl2]2 2. Evaluate the specific rate constant constant at the temperature at which the the data were collected. The rate-law 2 expression is rate = k [NO] [NO] [H2]. H2(g) + NO(g)
____
Initial [Cl 2] 0.35 M 0.35 M 1.00 M 1.00 M 0.50 M 0.50 M
+ H2O(g)
Initial [NO] ( M ) 0.30 0.60 0.60
Initial [H2] ( M M ) 0.35 0.35 0.70
Initial Rate ( M •s-1) 2.835 × 10-3 1.134 × 10-2 2.268 × 10-2
9.4 × 10-3 M -2•s-1 2.7 × 10-2 M -2•s-1 1.6 × 10-4 M -2•s-1 8.1 × 10-3 M -2•s-1 9.0 × 10-2 M -2•s-1
3. The half-life of the zero order reaction reaction A → B is 0.56 minutes. If the initial concentration of A is 3.4 M , what is the rate constant? a. 6.07 mol/L •min b. 1.24 mol/L •min c. 3.04 mol/L •min d. 0.619 mol/L •min e. 1.79 mol/L •min 4. The decomposition of dinitrogen dinitrogen pentoxide pentoxide obeys the rate-law expression expression rate = 0.080 min -1[N2O5]. If the initial concentration of N 2O5 is 0.30 M 0.30 M , what is the concentration after 2.6 minutes? N 2O5 → N2O3 + O2 a. 0.38 M 0.38 M b. 0.028 M 0.028 M c. 0.24 M 0.24 M d. 0.13 M 0.13 M e. 0.32 M 0.32 M
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5. At 300 K the reaction below obeys the rate law Rate =k [NOCl]2 where k = 2.8 × 10-5 M -1•s-1. 2NOCl → 2NO + Cl2 Suppose 1.0 mole of NOCl is introduced into a 2.0-liter container at 300 K. Evaluate the half-life of the reaction. a. 2.6 × 103 seconds b. 3.6 × 104 seconds c. 2.4 × 104 seconds d. 1.1 × 103 seconds e. 4.0 × 104 seconds
____
6. At 300 K the reaction below obeys the rate law rate = k [NOCl]2 where k = 2.8 × 10-5 M -1•s-1. 2NOCl → 2NO + Cl2
____
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Suppose 1.0 mole of NOCl is introduced into a 2.0-liter container at 300 K. How much NOCl will remain after 30 minutes? a. 0.77 mol b. 0.84 mol c. 0.87 mol d. 0.63 mol e. 0.95 mol 7. Given the following potential energy diagram for the one-step reaction X + Y → Z + R The arrow "c" represents the __________.
a. net energy of reaction for the forward reaction b. activation energy for the forward reaction c. net energy of reaction for the reverse reaction d. activation energy for the reverse reaction e. energy content for the reaction 8. Consider the hypothetical reaction shown below. A + 2B → AB2 Assume that the following proposed mechanism is consistent with the rate data. B B2 B A
+ + + +
B → B2 A → AB + B AB → AB2 2B → AB2
slow fast fast overall
Which one of the following statements must be true? The reaction is __________. a. first order in A, second order in B, and third order overall b. second order in B and second order overall
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c. first order in A and first order overall d. second order in B, zero order in A, and third order overall e. second order in A and second order overall 9. Consider the reaction below and its observed rate law expression. Which proposed mechanisms are consistent with the rate law expression? 2NO2 → 2NO + O2rate =k [NO2]2 I.
NO2 + NO2 → N2O4 N2O4 → N2 + 2O2 N2 + O2 → 2NO 2NO2 → 2NO + O2
slow fast fast overall
II.
NO2 → N + O2 NO2 + N → N2O2 N2O2 → 2NO 2NO2 → 2NO + O2
slow fast fast overall
III.
NO2 → NO + O O + NO2 → NO + O2 2NO2 → 2NO + O2
slow fast overall
a. I b. II c. III d. I and III e. another combination ____ 10. Consider the following reaction. What would be the equilibrium constant expression? 4Br 2(g) + CH4(g)
4HBr(g) + CBr 4(g)
a. K c = b. K c = c. K c = d. K c = e. K c = ____ 11. What is the value of K c for the reaction 2A(g) + 3B(g) [B] = 0.30 M , [C] = 0.10 M and [D] = 0.50 M ? a. 1.9 b. 0.15 c. 2.4 d. 0.51 e. 0.088
2C(g) + D(g) if at equilibrium [A] = 0.60 M ,
4 ____ 12. Consider the reaction 2NO2(g) N2O4(g) o A reaction is initiated at 100 C with 2.35 moles NO 2 in a 3.0 L reactor (no N 2O4 present). If the equilibrium concentration of N 2O4 is 0.25 M , What is the value of K c at 100°C? a. 0.25 b. 0.31 c. 3.2 d. 6.7 e. 0.15 ____ 13. Consider the following reaction in which all reactants and products are gases. 1.00 mol of A and 2.00 mol of B are placed in a 5.0-liter container. After equilibrium has been established, 0.50 mol of D is present in the container. Calculate the equilibrium constant, K c, for the reaction. A + 2B
2C + D
a. 1.0 b. 0.15 c. 0.33 d. 3.0 e. 5.0 ____ 14. Given the following reaction and its equilibrium constant at a certain temperature, N 2(g) + 3H2(g) 2NH3(g) K c = 3.6 × 108 calculate the numerical value of the equilibrium constant for the following reaction at the same temperature. NH3(g) a. b. c. d. e.
N2(g) + H2(g)
2.8 × 10-9 1.9 × 104 1.3 × 107 5.3 × 10-5 7.7 × 10-18
____ 15. The equilibrium constant for the following gas phase reaction is 0.50 at 600 °C. A mixture of HCHO, H 2, and CO is introduced into a flask at 600 °C. After a short time, analysis of a small amount of the reaction mixture shows the concentrations to be [HCHO] = 1.5 M , [H2] = 0.5 M , and [CO] = 1.0 M . Which of the following statements about this reaction mixture is true? HCHO
H2 + CO
a. The reaction mixture is at equilibrium. b. The reaction mixture is not at equilibrium, but no further reaction will occur. c. The reaction mixture is not at equilibrium, but will move toward equilibrium by forming more HCHO. d. The reaction mixture is not at equilibrium, but will move toward equilibrium by using up more HCHO. e. The forward rate of this reaction is the same as the reverse rate. ____ 16. At a certain temperature K c = 55 and a reaction vessel contains a mixture with the following concentrations : [SO3] = 0.85 M , [NO] = 1.2 M , [SO2] = 1.5 M and [NO2] = 2.0 M . Which of the following statements concerning the reaction and the reaction quotient, Q, is false? SO3(g) + NO(g)
SO2(g) + NO2(g)
a. Q < K c b. Q > K c c. The reaction is not in equilibrium.
5 d. Product concentrations will increase as equilibrium is approached. e. Reactant concentrations will decrease as equilibrium is approached. ____ 17. A quantity of HI was sealed in a tube, heated to 425 °C, and held at this temperature until equilibrium was reached. The concentration of HI in the tube at equilibrium was found to be 0.0706 moles/liter. Calculate the equilibrium concentration of H 2 (and I2). For the reaction H 2(g) + I2(g)
2HI(g), K c = 54.6 at 425 °C.
4.78 × 10-3 M 9.55 × 10-3 M 2.34 × 10-3 M 1.17 × 10-3 M 1.85 × 10-4 M ____ 18. The equilibrium constant for the following gas phase reaction is 4.0 at a certain temperature. A reaction is carried out at this temperature starting with 2.0 mol/L of CO and 2.0 mol/L of H 2O. What will be the equilibrium concentration of H 2? a. b. c. d. e.
CO + H2O a. b. c. d. e.
CO2 + H2
2.0 M 0.75 M 1.3 M 0.67 M 1.5 M
____ 19. Exactly one mol/L of each of the four gases involved in the following reaction is placed in a reactor at 200 °C and allowed to reach equilibrium. What is the equilibrium concentration of H 2O? K c = 2.38 @ 200 °C. CO(g) + H2O(g)
CO2(g) + H2(g)
a. 1.21 M b. 0.213 M c. 0.787 M d. 2.38 M e. 1.0 M ____ 20. Consider the following reaction involving a solid. 3Fe(s) + 4H2O(g)
Fe3O4(s) + 4H2(g)
The appropriate equilibrium constant expression would be: a.
b.
c.
6 d.
e.
____ 21. Consider the system below at equilibrium at 200 °C. 2Cl2(g) + 2H2O(g) + heat
4HCl(g) + O2(g)
Which response contains all the stresses listed that will result in a shift of the equilibrium so that more HCl is produced when equilibrium is re-established, and no stresses that will not? I. II. III.
adding some Cl2 raising the temperature at constant pressure decreasing the volume at constant temperature
a. I and II b. II and III c. III d. I and II e. another one or another combination ____ 22. At equilibrium a 1.0-liter container was found to contain 0.20 mol of A, 0.20 mol of B, 0.40 mol of C, and 0.40 mol of D. If 0.10 mol of A and 0.10 mol of B are added to this system, which of the following statements is true? A(g) + B(g)
C(g) + D(g)
a. The system remains in equilibrium. b. Q > K c c. More reactants are formed to increase the value of Q. d. The value of K c decreases. e. More products are formed to increase the value of Q ____ 23. A system at equilibrium in a 1.0-liter container was found to contain 0.20 mol of A, 0.20 mol of B, 0.40 mol of C, and 0.40 mol of D. If 0.12 mol of A and 0.12 mol of B are added to this system, what will be the new equilibrium concentration of C? A(g) + B(g) a. b. c. d. e.
0.32 M 0.13 M 0.24 M 0.40 M 0.48 M
C(g) + D(g)
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General Chemistry II Answer Section
Practice Problems for Exam 2
MULTIPLE CHOICE
1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17. 18. 19. 20. 21. 22. 23. 24.
ANS: ANS: ANS: ANS: ANS: ANS: ANS: ANS: ANS: ANS: ANS: ANS: ANS: ANS: ANS: ANS: ANS: ANS: ANS: ANS: ANS: ANS: ANS: ANS:
D E C C B E D B A C D C A D D B B C C B A E E A
TOP: TOP: TOP: TOP: TOP: TOP: TOP: TOP: TOP: TOP: TOP: TOP: TOP: TOP: TOP: TOP: TOP: TOP: TOP: TOP: TOP: TOP: TOP: TOP:
Concentrations of Reactants: the Rate-Law Expression Concentrations of Reactants: the Rate-Law Expression Concentration Versus Time: The Integrated Rate Equation Concentration Versus Time: The Integrated Rate Equation Concentration Versus Time: The Integrated Rate Equation Concentration Versus Time: The Integrated Rate Equation Collision Theory and Transition State Theory Reaction Mechanisms and the Rate-Law Expression Reaction Mechanisms and the Rate-Law Expression Basic Concepts and the Equilibrium Constant Basic Concepts and the Equilibrium Constant Basic Concepts and the Equilibrium Constant Basic Concepts and the Equilibrium Constant Variation of Kc with the Form of the Balanced Equation The Reaction Quotient The Reaction Quotient Uses of the Equilibrium Constant, Kc Uses of the Equilibrium Constant, Kc Uses of the Equilibrium Constant, Kc Basic Concepts and the Equilibrium Constant Disturbing a System in Equilibrium: Predictions Disturbing a System in Equilibrium: Predictions Disturbing a System in Equilibrium: Calculations Disturbing a System in Equilibrium: Calculations
