ADDITIONAL PROBLEMS CHEMICAL EQUILIBRIUM

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1 ADDITIONAL PROBLEMS CHEMICAL EQUILIBRIUM Basic Concepts and the Equilibrium Constant 1. Which of the statements concerning equilibrium is false? (a) (b) (c) (d) (e) A system that is disturbed from an equilibrium condition responds in a manner to restore equilibrium. Equilibrium in molecular systems is dynamic, with two opposing processes balancing one another. The value of the equilibrium constant for a given reaction mixture is the same regardless of the direction from which equilibrium was attained. A system moves spontaneously toward a state of equilibrium. The equilibrium constant usually is independent of temperature. ANSWER: (e) 2. Which of the following is the best definition of chemical equilibrium? (a) A condition where the forward and reverse reaction rates of a reversible reaction are equal and constant. (b) There are equal amounts of reactants and products. (c) The forward and reverse reaction rates have stopped. (d) The product concentrations are larger than reactant concentrations. (e) The reactant concentrations are larger than product concentrations. 3. When the system A + B C + D is at equilibrium, (a) the forward reaction has stopped. (b) the reverse reaction has stopped. (c) both the forward and the reverse reactions have stopped. (d) neither the forward nor the reverse reaction has stopped. (e) the sum of the concentrations of A and B must equal the sum of the concentrations of C and D. 313

2 Consider the gas phase system below at a high temperature. The form of the expression for the equilibrium constant, K c,. 4NH 3 + 5O 2 4NO + 6H 2 O (a) cannot be determined without rate data (b) is K c = [NH 3][O 2 ] [NO][H 2 O] (d) is K c = [NO] 4 [NH 3 ][O 2 ] (c) is K c = [NH 3] 4 [O 2 ] 5 [NO] 4 [H 2 O] 6 (e) is K c = [NO]4 [H 2 O] 6 [NH 3 ] 4 [O 2 ] 5 Answer: (e) 5. Consider the following reaction involving a solid. 3Fe(s) + 4H 2 O(g) Fe 3 O 4 (s) + 4H 2 (g) The appropriate equilibrium constant expression would be: (a) [H 2 O] 4 (b) [H 2 ] 4 (c) [Fe 3 O 4 ][H 2 ] [H 2 ] 4 [H 2 O] 4 [Fe][H 2 O] (d) [Fe 3 O 4 ][H 2 ] 4 (e) [Fe] 3 [H 2 O] 4 [Fe] 3 [H 2 O] 4 [Fe 3 O 4 ][H 2 ] 4 6. What is the value of K c for the reaction 2A(g) + 3B(g) 2C(g) + D(g) if at equilibrium [A] = 0.60 M, [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) What is the value of K c for the reaction CH 4 (g) + H 2 O(g) CO(g) + 3H 2 (g) if at equilibrium [CH 4 ] = 0.20 M, [H 2 O] = 0.20 M, [CO] = 0.50 M and [H 2 ] = 1.50 M? (a) 19 (b) 0.24 (c) (d) 42 (e) 16

3 8. In a 1.0-liter container there are, at equilibrium, 0.10 mole H 2, 0.20 mole N 2, and 0.40 mole NH 3. What is the value of K c for this reaction at this temperature? N 2 (g) + 3H 2 (g) 2NH 3 (g) (a) (b) 20 (c) 8.0 x 10 2 (d) (e) Some nitrogen and hydrogen gases are pumped into an empty 5.00-liter vessel at 500 C. When equilibrium was established, 3.00 moles of N 2, 2.10 moles of H 2, and moles of NH 3 were present. Evaluate K c at 500 C. N 2 (g) + 3H 2 (g) 2NH 3 (g) (a) (b) 0.63 (c) 0.96 (d) (e) Nitrogen oxide and bromine combine to form nitrosyl bromide, NOBr. 2NO(g) + Br 2 (g) 2NOBr(g) In a 5.0 liter reactor at equilibrium at a constant temperature, it was determined there was 0.45 mol NO, 0.17 mol Br and 1.32 mol NOBr. What is the value of K c at this temperature? (a) (b) 86.2 (c) 253 (d) (e) Consider the reaction 2NO 2 (g) N 2 O 4 (g) A reaction is initiated at 100 o C with 2.35 moles NO 2 in a 3.0 L reactor (no N 2 O 4 present). If the equilibrium concentration of N 2 O 4 is 0.25 M, What is the value of K c at 100 o C? (a) 0.25 (b) 0.31 (c) 3.2 (d) 6.7 (e) The reversible reaction 2SO 2 (g) + O 2 (g) 2SO 3 (g) has come to equilibrium in a vessel of specific volume at a given temperature. Before the reaction began, the concentrations of the reactants were mol/l of SO 2 and mol/l of O 2. After equilibrium is reached, the concentration of SO 3 is mol/l. What is the value of K c?

4 316 (a) 2.7 (b) 1.3 x 10 2 (c) 7.5 x 10 3 (d) 0.38 (e) 40. Variation of K c with the Form of the Balanced Equation 13. The equilibrium constant for the reaction CO(g) + H 2 O(g) CO 2 (g) + H 2 (g) is 26 at 50 o C. What is K c for 3CO 2 (g) + 3H 2 (g) 3CO(g) + 3H 2 O(g) at the same temperature? (a) 0.34 (b) 1.8 x 10 4 (c) (d) 5.7 x 10-5 (e) 2.9 Answer (d) 14. Given the following reaction and its equilibrium constant at a certain temperature, N 2 (g) + 3H 2 (g) 2NH 3 (g) K c = 3.6 x 10 8 calculate the numerical value of the equilibrium constant for the following reaction at the same temperature. NH 3 (g) 1 2 N 2 (g) H 2 (g) (a) 2.8 x 10 9 (b) 1.9 x 10 4 (c) 1.3 x 10 7 (d) 5.3 x 10 5 (e) 7.7 x Answer (d) 15. If the equilibrium constant at a certain temperature is 2.1 x for the following reaction, 4HCl(g) + O 2 (g) 2Cl 2 (g) + 2H 2 O(g) calculate the value of the equilibrium constant at the same temperature for Cl 2 (g) + 2 H 2 O(g) HCl(g) + O 4 2(g). (a) 2.2 x 10 7 (b) 3.8 x 10 3 (c) 5.3 x (d) 4.7 x 10 4 (e) 1.2 x Answer (d)

5 The Reaction Quotient 16. Which of the following statements about the reaction quotient, Q is false? (a) The value of Q can be used to predict equilibrium concentrations. (b) It has the same expression as K c. (c) Its value is calculated using nonequilibrium concentrations. (d) If Q > K c, the reaction must move to equilibrium by forming more reactants. (e) If Q < K c, the reaction must move to equilibrium by forming more products. 17. 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, [H 2 ] = 0.5 M, and [CO] = 1.0 M. Which of the following statements about this reaction mixture is true? HCHO H 2 + 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. 18. The equilibrium constant, K c, 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, [H 2 ] = 1.2 M, and [CO] = 1.0 M. Which of the following statements about this reaction mixture is true? HCHO H 2 + CO (a) (b) (c) (d) (e) The reaction mixture is at equilibrium. The reaction mixture is not at equilibrium, but no further reaction will occur. The reaction mixture is not at equilibrium, and will move toward equilibrium by forming more HCHO. The reaction mixture is not at equilibrium, and will move toward equilibrium by using up more HCHO. The forward rate of this reaction is the same as the reverse rate.

6 The equilibrium constant, K c,for the following reaction is at a high temperature. A mixture in a container at this temperature has the concentrations : [H 2 ] = 1.11 M, [I 2 ] = 1.30 M and [HI] = M. Which of the following statements concerning the reaction and the reaction quotient, Q, is true? H 2 (g) + I 2 (g) 2HI(g) (a) Q = K c (b) Q > K c ; more HI will be produced. (c) Q > K c ; more H 2 and I 2 will be produced. (d) Q < K c ; more HI will be produced. (e) Q < K c ; more H 2 and I 2 will be produced. 20. At a certain temperature K c = 25 and a reaction vessel contains a mixture with the following concentrations : [H 2 ] = 0.10 M, [Br 2 ] = 0.10 M and [HBr] = 0.50 M. Which of the following statements concerning the reaction and the reaction quotient, Q, is true? H 2 (g) + Br 2 (g) 2HBr(g) (a) Q = K c (b) Q < K c ; more HBr will be produced. (c) Q < K c ; more H 2 and Br 2 will be produced. (d) Q > K c ; more HBr will be produced. (e) Q > K c ; more H 2 and Br 2 will be produced. Uses of the Equilibrium Constant, K c 21. For the gas phase reaction N 2 O 4 2NO 2, K c = 8. If 2 moles of N 2 O 4 is introduced into a 1-liter vessel, the number of moles (not concentration) of NO 2 at equilibrium, x, can be calculated from the equation: x (a) 8 = 2 x 2 x 2 (d) 8 = 2 x 2 (b) 8 = 4x2 2 x (e) 8 = x 2 2 x (c) 8 = x2 2

7 22. Nitrosyl chloride, NOCl, dissociates on heating as shown below. When a gram sample of pure NOCl is heated at 350 C in a volume of 1.00 liter, the percent dissociation is found to be 57.2%. Calculate the equilibrium concentration of NOCl. NOCl(g) NO(g) Cl 2 (g) (a) 8.76 x 10 1 M (b) 9.26 M (c) 9.80 x 10 3 M (d) 1.31 x 10 2 M (e) 1.75 x 10 4 M 23. The numerical value of the equilibrium constant, K c, for the following gas phase reaction is 0.50 at a certain temperature. When a certain reaction mixture reaches equilibrium, the concentration of O 2 is found to be 2.0 M, while the concentration of SO 3 is found to be 10 M. What is the equilibrium concentration of SO 2 in this mixture? 2SO 2 + O 2 2SO 3 (a) 0.50 M (b) 10 M (c) 0.10 M (d) 5.0 M (e) 1.0 M 24. For the reaction 3O 2 O 3 the value of the equilibrium constant is at a particular temperature. If the equilibrium concentration of [O 2 ] is 0.75 M, what is the equilibrium concentration of O 3? (a) M (b) 0.22 M (c) 0.75 M (d) M (e) M 25. Consider the following system. The equilibrium constant for the reaction at 900 C is A reaction is initiated with only COCl 2 in a 2.0-liter vessel. At equilibrium 2.36 x 10 3 mol of Cl 2 is present. How many moles of COCl 2 are present at equilibrium? COCl 2 (g) CO(g) + Cl 2 (g) Answer: (e) (a) 1.4 x 10 4 mol (b) 1.4 x 10 3 mol (c) 6.1 x 10 5 mol (d) 5.8 x 10 4 mol (e) 3.4 x 10 5 mol 26. 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 moles/liter. Calculate the equilibrium concentration of H 2 (and I 2 ). For the reaction H 2 (g) + I 2 (g) 2HI(g), K c = 54.6 at 425 C. (a) 4.78 x 10 3 M (b) 9.55 x 10 3 M (c) 2.34 x 10 3 M (d) 1.17 x 10 3 M (e) 1.85 x 10 4 M

8 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 2 O. What will be the equilibrium concentration of H 2? CO + H 2 O CO 2 + H 2 (a) 2.0 M (b) 0.75 M (c) 1.3 M (d) 0.67 M (e) 1.5 M 28. For the following reaction, K c is 144 at 200 C. If mol of both A and B are placed in a 2.00-liter container at that temperature, what will be the concentration of C at equilibrium? A(g) + B(g) C(g) + D(g) (a) M (b) 1.64 M (c) M (d) M (e) 1.13 M 29. Ammonium carbamate decomposes into NH 3 and CO 2 when heated. NH 4 (NH 2 CO 2 )(s) 2NH 3 (g) + CO 2 (g) If 25.0 g of ammonium carbamate is placed in an empty chamber and heated to 100 o C, what are the equilibrium concentrations of NH 3 and CO 2? Kc = 58.3 at 100 o C. M M (a) [NH 3 ] = 2.44 M, [CO 2 ] = 4.88 M (b) [NH 3 ] = 4.88 M, [CO 2 ] = 2.44 (c) [NH 3 ] = 29.2 M, [CO 2 ] = 14.6 M (d) [NH 3 ] = 15.3 M, [CO 2 ] = 7.64 (e) [NH 3 ] = 10.8 M, [CO 2 ] = 5.40 M 30. At 25 C, K c for the following reaction is 4.66 x If mol of N 2 O 4 is injected into a closed 1.00-liter glass container at 25 C, what will be the equilibrium concentration of N 2 O 4? N 2 O 4 (g) 2NO 2 (g) (a) M (b) M (c) M (d) M (e) M 31. Exactly one mol/l of each of the four gases involved in the following reaction is placed in a reactor at 200 o C and allowed to reach equilibrium. What is the equilibrium concentration of H 2 O? K c = 200 o C.

9 CO(g) + H 2 O(g) CO 2 (g) + H 2 (g) (a) 1.21 M (b) M (c) M (d) 2.38 M (e) 1.0 M 32. Phosgene, COCl 2, is a poisonous gas that decomposes into carbon monoxide and chlorine according to the following equation with K c = at 900 C. If the reaction is initiated with mole of COCl 2 at 900 C in a 5.00-liter container, what concentration of CO will be present after equilibrium is established? COCl 2 (g) CO(g) + Cl 2 (g) Answer (c) (a) M (b) M (c) M (d) M (e) M 33. For the following system, the equilibrium constant at 445 C is If a reaction is initiated with the following initial concentrations, [H 2 ] = 2.06 x 10 2 M, [I 2 ] = 1.45 x 10 2 M, and [HI] = 0, what will be the equilibrium concentration of HI? H 2 (g) + I 2 (g) 2HI(g) (a) 1.8 x 10 2 M (b) 1.4 x 10 1 M (c) 2.7 x 10 1 M (d) 2.6 x 10 2 M (e) 3.7 x 10 3 M 34. At 990 C, K c = 1.6 for the following reaction. How many moles of H 2 O(g) are present in an equilibrium mixture resulting from the addition of 1.00 mole of H 2, 2.00 mol of CO 2, 0.75 mol of H 2 O, and 1.00 mol of CO to a 5.00-liter container at 990 C? H 2 (g) + CO 2 (g) H 2 O(g) + CO(g) (a) 0.60 mol (b) 0.80 mol (c) 1.02 mol (d) 1.45 mol (e) 1.14 mol Answer: (e) Disturbing a System in Equilibrium: Le Chatelier s Principle 35. Which statement best represents LeChatelier s Principle? (a) A system in equilibrium will always remain in equilibrium. (b) Only a change in equilibrium will affect the equilibrium of a reaction. (c) When a change is made to a system in equilibrium, equilibrium can never be restored.

10 322 (d) A system in equilibrium will respond to a change by moving in the direction that reduces the change as it returns to equilibrium. (e) A system in equilibrium will not be affected by a change in concentration. 36. For the system H 2 (g) + CO 2 (g) H 2 O(g) + CO(g) at equilibrium, the addition of H 2 (g) would cause (according to LeChatelier's principle) (a) only more H 2 O(g) to form. (b) only more CO(g) to form. (c) more H 2 O(g) and CO(g) to form. (d) only more CO 2 (g) to form. (e) no change in amounts of products or reactants. Answer (c) 37. For the system H 2 (g) + CO 2 (g) H 2 O(g) + CO(g) at equilibrium, the removal of some of the H 2 O(g) would cause (according to LeChatelier's principle) (a) more H 2 (g) to be form. (b) more CO 2 (g) to be form. (c) no change in the amounts of products or reactants. (d) more CO(g) to be form. (e) the amount of CO(g) to remain constant while the amount of H 2 O(g) increases to the original equilibrium concentration. 38. If the system below is at equilibrium in a closed vessel and a small amount of nitrous acid is added, what would be expected to happen? HN 3 (l) + 2H 2 O(l) N 2 H 4 (l) + HNO 2 (l) H 0 = +641 kj hydrazoic hydrazine nitrous acid acid (a) Some HN 3 would be used up in re-establishing equilibrium. (b) Some HNO 2 would be formed in re-establishing equilibrium. (c) Some HNO 2 would be formed, and some N 2 H 4 would be lost. (d) More HN 3 and H 2 O would be formed. (e) The temperature would decrease, and the forward reaction would be favored.

11 39. Consider the following systems at equilibrium. Which response includes all the stresses listed that would shift the equilibrium to the right (favor the forward reaction)? Equilibrium Stress I. CO(g) + Cl 2 (g) COCl 2 (g) add Cl 2 II. CO(g) + Cl 2 (g) COCl 2 (g) remove COCl 2 III. PCl 3 (g) + Cl 2 (g) PCl 5 (g) remove PCl 3 (a) I (b) III (c) I and II (d) II and III (e) I, II and III 40. Consider the reaction A(g) + B(g) D(g) + Heat Which of the following sets of reaction conditions would produce the maximum yield of product? (a) 100 o C, 50 atm, (b) 100 o C, 10 atm, (c) 500 o C, 50 atm, catalyst (d) 100 o C, 10 atm, catalyst (e) 100 o C, 50 atm, catalyst Answer (e) 41. Suppose we let the reaction below come to equilibrium. Then we decrease the total pressure, by increasing the volume of the container. What will be the effect on the numerical value of the equilibrium constant, K? 2SO 2 (g) + O 2 (g) 2SO 3 (g) + heat (a) It increases. (b) It decreases. (c) It does not change. (d) The question cannot be answered without knowing the initial value of K. (e) The question cannot be answered without knowing the value of H Suppose the following reaction is at equilibrium at a given temperature and pressure. The pressure is then increased at constant temperature, by compressing the reaction mixture, and the mixture is allowed to re-establish equilibrium. At the new equilibrium. H 2 (g) + Cl 2 (g) 2HCl(g) (a) there is more hydrogen chloride than there was originally (b) there is less hydrogen chloride than there was originally (c) there is the same amount of hydrogen chloride as there was originally (d) the hydrogen and chloride are completely used up (e) the amount of hydrogen chloride may be either larger or smaller than it was originally, depending on the value of K

12 Decreasing the volume of the container (at constant temperature) after the system below has reached equilibrium would be expected to. HN 3 (l) + 2H 2 O(l) N 2 H 4 (l) + HNO 2 (l) (a) produce more HN 3 and raise the temperature (b) produce more H 2 O and lower the temperature (c) produce more N 2 H 4 and raise the temperature (d) produce more HNO 2 and lower the temperature (e) have no effect on this equilibrium Answer: (e) 44. Suppose we let this reaction come to equilibrium. Then we increase the temperature of the reaction mixture. What will be the effect on the net amount of SO 3 (g) present? 2SO 2 (g) + O 2 (g) 2SO 3 (g) + heat (a) It increases. (b) It decreases. (c) It does not change. (d) The question cannot be answered without knowing the value of K. (e) The question cannot be answered without knowing the value of H Which of the numbered responses lists all of the following stresses that would shift the equilibrium to the left (favor the reverse reaction), and no other stresses? 2NOCl(g) + 75 kj 2NO(g) + Cl 2 (g) I. Add a catalyst. II. Heat the mixture. III. Decrease the volume at constant temperature. IV. Increase the partial pressure of NOCl by adding NOCl. (a) I, II, and IV (b) II, III, and IV (c) II and III (d) III (e) a different one or a different combination 46. Consider the reaction below at equilibrium at a certain temperature. 2SO 2 (g) + O 2 (g) 2SO 3 (g) + heat Which response contains all the stresses that would shift the equilibrium so as to produce more SO 3 (to the right), and only those stresses? I. increase temperature at constant pressure II. decrease the volume of the system at constant pressure

13 Answer: (e) III. remove SO 2 IV. add O 2 V. increase the partial pressure of SO 2 (a) II and III (b) I, II, and IV (c) I and V (d) I and III (e) II, IV, and V 47. 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 Answer: (e) Disturbing a System in Equilibrium: Calculations 48. 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 0.15 mol of A and 0.15 mol of B are added to this system, what will be the new equilibrium concentration of A? A(g) + B(g) C(g) + D(g) (a) M (b) 0.10 M (c) 0.20 M (d) 0.25 M (e) 0.30 M d 74. 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, what will be the new equilibrium concentration of A? A(g) + B(g) C(g) + D(g) (a) 0.37 M (b) 0.47 M (c) 0.87 M (d) 0.23 M (e) M

14 A 1.00-liter vessel contains the following equilibrium concentrations at 400 C: N 2, 1.00 M; H 2, 0.50 M; and NH 3, 0.50 M. How many moles of hydrogen must be removed from the vessel in order to increase the concentration of nitrogen to 1.20 M? N 2 (g) + 3H 2 (g) 2NH 3 (g) (a) 0.94 mol (b) 1.5 mol (c) 0.33 mol (d) 0.76 mol (e) 1.1 mol 50. Given: PCl 5 (g) PCl 3 (g) + Cl 2 (g) K c = at 450 C What would be the equilibrium concentration of PCl 5 (g) if 0.20 mole of PCl 5 (g) was placed in a 1.00-L container at this temperature? What would be the new equilibrium concentration of PCl 5 (g) if the volume were halved at this same temperature? (a) M, 0.29 M (b) 0.13 M, 0.29 M (c) 0.13 M, 0.11 M (d) M, 0.13 M (e) M, 0.14 M 51. Given: N 2 (g) + O 2 (g) 2NO(g) K c = 0.16 What would be the equilibrium concentration of N 2 (g) if 0.12 mole of NO(g) was placed in a 1.00-L container at this temperature? What would be the new equilibrium concentration of N 2 (g) if the volume were halved at this same temperature? (a) M, 0.10 M (b) M, 0.12 M (c) M, 0.12 M (d) 0.10 M, 0.10 M (e) 0.50 M, 1.0 M Partial Pressures and the Equilibrium Constant 52. When equilibrium is established for the following reaction at 298 K, the concentration of N 2 O 4 is 1.34 mol/l, and the concentration of NO 2 is mol/l. Convert these concentrations to partial pressures. What is the total pressure of the system at equilibrium? N 2 O 4 (g) 2NO 2 (g) (a) 2.54 atm (b) 11.6 atm (c) 16.7 atm (d) 34.4 atm (e) 43.8 atm

15 53. A mixture of 0.40 mol of N 2, 0.60 mol of Ar, and 0.30 mol of O 2 is confined in a 300-liter vessel at 50.0 C. What is the total pressure of the system? Answer: (e) (a) 0.32 atm (b) atm (c) atm (d) atm (e) 0.11 atm 54. For the following gas-phase reaction at 400 K, 2A B + C, K P = If initially the total pressure in the reactor is 1.80 atm and only A is present, what is the total pressure in the reactor at equilibrium? (a) 2.20 atm (b) 3.54 atm (c) atm (d) 17.1 atm (e) 1.80 atm Answer: (e) 55. Phosphorus pentafluoride, PF 5 (g), partially decomposes to PF 3 (g) and F 2 (g) at a temperature of 600 K. A 2.0-liter container is filled with pure PF 5. At a temperature of 600 K, the initial pressure of PF 5 is 2.0 atm. When equilibrium is reached, half of the original amount of PF 5 has decomposed. The equilibrium constant, K p, for PF 5 (g) PF 3 (g) + F 2 (g) is. (a) (b) 0.12 (c) 0.25 (d) 0.50 (e) 1.0 Answer: (e) Relationship Between K p and K c 56. Consider the reversible reaction at equilibrium at 392 C. 2A(g) + B(g) C(g) The partial pressures are found to be: A: 6.70 atm, B: 10.1 atm, C: 3.60 atm. What is the concentration of B at equilibrium? (a) M (b) 1.64 M (c) M (d) M (e) 1.13 M 57. K c = 4.6 x 10 3 for the reaction below at 25 C. Evaluate K p at 25 C. N 2 O 4 (g) 2NO 2 (g) (a) (b) 0.11 (c) 6.2 x 10 3

16 328 (d) 1.9 x 10 4 (e) 3.2 x K c = 2.3 x 10 2 for the reaction below at 100 C. Evaluate K p at 100 C. CO 2 (g) + H 2 (g) CO(g) + H 2 O(g) (a) 43.5 (b) 2.3 x 10 2 (c) 1.73 (d) 7.0 x 10 4 (e) 7.5 x Given: PCl 5 (g) PCl 3 (g) + Cl 2 (g) At 250. C a sample of PCl 5 was placed in a 24-liter evacuated reaction vessel and allowed to come to equilibrium. Analysis showed that at equilibrium 0.42 mole of PCl 5, 0.64 mole of PCl 3, and 0.64 mole of Cl 2 were present in the vessel. Calculate K p for the reaction at 250. C. (a) 1.2 (b) 1.3 (c) 1.5 (d) 1.8 (e) Certain amounts of the hypothetical substances A 2 and B are mixed at 300. K. When equilibrium is established for the reaction below, the following amounts were present in a 3.00-liter container: mole of A 2, mole of B, mole of D, and mole of E. What is K p, the equilibrium constant, in terms of partial pressures (atm), for this reaction? A 2 (g) + 3B(g) 2D(g) + 3E(g) (a) 16.4 (b) (c) 3.81 x 10 2 (d) 2.57 x 10 2 (e) 1.46 x Certain amounts of the hypothetical substances A 2 and B are mixed in a 3.00-liter container at 300. K. When equilibrium is established for the reaction the following amounts are present: mol of A 2, mol of B, mol of D, and mol of E. What is K p, the equilibrium constant in terms of partial pressures, for this reaction? A 2 (g) + 3B(g) 2D(g) + E(g) (a) 16.4 (b) (c) 3.81 x 10 2 (d) 1.42 x 10 2 (e) 2.50 x For the reaction below, K p = 1.59 at 100 o C. If 1.0 g of SrCO 3 is placed in an empty 5.00 L reactor and allowed to reach equilibrium, what will be the pressure in the reactor?

17 SrCO 3 (s) SrO(s) + CO 2 (g) (a) 1.59 atm (b) 1.26 atm (c) 2.53 atm (d) 1.0 atm (e) 3.18 atm 63. The gas phase system below is at equilibrium at 200 C with the following partial pressures: 0.20 atm A, 0.20 atm B, 0.10 atm C, and 0.40 atm D. If an additional 0.30 atm C is introduced into the reaction vessel, what will be the partial pressure of C at 200 C when equilibrium is re-established? A(g) + B(g) C(g) + D(g) (a) 0.60 atm (b) 0.30 atm (c) 0.50 atm (d) 0.75 atm (e) 0.45 atm Relationship Between G 0 and the Equilibrium Constant 64. Calculate the thermodynamic equilibrium constant at 25 C for a reaction for which G 0 = 11.3 kj per mol of reaction. R = J/mol K (a) (b) 95.7 (c) 4.56 (d) 1.04 x 10-2 (e) 4.32 x Evaluate the thermodynamic equilibrium constant for the following reaction at 25 o C. CH 4 (g) + H 2 O(g) CO(g) + 3H 2 (g) G o f kj/mol (a) 5.5 x (b) 2.2 x (c) 3.4 x (d) 4.4 x (e) 1.8 x 10 75