CHEMpossible. Final Exam Review

Transcription

1 CHEMpossible Final Exam Review 1. Given the following pair of reactions and their equilibrium constants: 2NO 2 (g) 2NO (g) + O 2 (g) K c = NO (g) + Cl 2 (g) 2 NOCl (g) K c = Calculate a value for K C for the reaction: 2NOCl (g) + O 2 (g) 2NO 2 (g) + Cl 2 (g) 2. At 250, the equilibrium constant K p for the reaction PCl 5 (g) PCl 3 (g) + Cl 2 (g) is Sufficient PCl 5 is put into a reaction vessel to give an initial pressure of 2.74 atm at 250 C. Calculate the pressure of PCl 5 after the system has reached equilibrium. a atm b atm c atm d atm e atm 3. Which equilibrium can be described as an acid-base reaction using the Lewis acid-base definitions, but not using the Bronsted-Lowry definitions? a. NH 3 + CH 3 COOH CH 3 COO NH 4 b. H 2 O + CH 3 COOH H 3 O + + CH 3 COO c. 4NH 3 + Cu(H 2 O) 2+ 4 Cu(NH 3 ) H 2 O d. 2NH 3 + H 2 SO 4 2NH SO 2-4 e. Fe(H 2O) H 2O H 3O + + Fe(H 2O) 5(OH) The ph of a solution is 5. If the ph of this solution is decreased to 2, by what factor is the concentration of hydrogen ion increased? a. 2.5 b. 3 c. 10 d. 100 e. 1000

2 5. For a substance to be considered a strong electrolye, it must a. Be an ionic compound b. Dissociate virtually completely to its ions in solution c. Be highly soluble in water d. Contain both metal and nonmetal ions 6. To what volume must 150 ml of a 3.60 M soln be diluted to prepare a solution which is 2.40 M? a ml b. 444 ml c. 285 ml d. 225 ml 7. When water molecules in the liquid state enter the gaseous state we can say that a. The intermolecular forces have weakened. b. The intramolecular forces have weakened. c. The intermolecular forces have strengthened. d. The intramolecular forces have strengthened. e. Both the inter and intramolecular forces have weakened. 8. Which of the following would have the lowest freezing point? a. Pure H 2 O b. 1 m urea (CON 2 H 4 ) c. 1 m KCl d. 1 m NaNO 3 e. 1 mna 2 SO 4 9. At equilibrium a. All chemical processes have ceased. b. The rate of the forward reaction equals that of the reverse. c. The rate constant for the forward reaction equals that of the reverse. d. Both the rate of the forward reaction equals that of the reverse and the rate constant for the forward reaction equals that of the reverse. e. None of the above. 10. A 1.00 L flask contained 0.24 mol NO 2 at 700 K, which decomposed according to the following equation. When equilibrium was achieved, 0.14 mol NO was present. Calculate K. 2NO 2 (g) 2 NO (g) + O 2 (g) a b c d e

3 11. The ph of a 4.52 M solution of a weak acid is 3.90 at 25 C. What is K a for the weak acid? a b c d e In which reaction will an increase in total pressure at constant temperature favor formation of the products? a. CaCO 3 (s) CaO(s) + CO 2 (g) b. H 2 (g) + Cl 2 (g) 2HCl (g) c. 2NO (g) + O 2 (g) 2NO 2 (g) d. COCl 2 (g) CO (g) + Cl 2 (g) 13. A reaction has an activation energy of 40 kj and an overall energy change of -100 kj. What is the potential energy diagram which best describes this reaction? 14. In general, as the temperature increases, the rate of a chemical reaction a. Increases due to an increased activation energy. b. Increases only for an endothermic reaction. c. Increases due to a greater number of effective collisions. d. Increases because bonds are weakened. e. Is not changed. 15. If a process is exothermic and not spontaneous, then what must be true? a. ΔS > 0 b. ΔH > 0 c. ΔG = 0 d. ΔS < 0 e. ΔH = Consider the equation: 2NaI (aq) + Cl 2 (g) I 2 (aq) + 2NaCl (aq) The element undergoing reduction is: a. Sodium b. Iodide c. Chlorine d. Iodine e. Water

4 17. A 25.0 ml sample of M HCl is mixed with 15.0 ml of M of NaOH. The ph of the resulting solution will be nearest a. 2.1 b. 7.0 c d If you need 50.0 ml of a M KMnO 4 solution, which method do you use to prepare it? a. Dissolve 39.5 g KMnO 4 in enough water to make 50.0 ml solution b. Dissolve 12.5 g KMnO 4 in enough water to make 50.0 ml solution c. Dissolve 1.98 g KMnO 4 in enough water to make 50.0 ml solution d. Dilute 20.0 ml of M KMnO 4 to 50.0 ml e. Dilute 2.50 ml of 1.00 M KMnO 4 to 50.0 ml 19. Which statement correctly expresses a relation between solubility and temperature? a. An increase in temperature increases the solubility of a gas in a liquid b. The change of solubility with temperature is the same for all substances. c. The solubility of a liquid in a liquid is independent of temperature d. The solubility of most solids in water increases with increasing temperature e. The solubility of most solids in water decreases with increasing temperature 20. What is the mole fraction of water in g of 95% by mass ethanol, C 2 H 5 OH? a b c d A 0.10 m aqueous solution of HF shows a freezing point of C. What is the percent dissociation of HF? (K f for water = 1.86 C/m) a. 6.4% b. 10% c. 20% d. 98% 22. Under which of the following conditions does the equilibrium constant K change for the reaction H 2 (g) + I 2 (g) 2 HI (g) a. Changing the size of the container b. Introducing more I 2 into the container c. Measuring the molar concentrations instead of pressures d. Changing the temperature e. None of these, it is always constant

5 23. If you mix equal molar quantities of the following, how many will produce an acidic solution? Set 1: NaOH + HCl Set 2: NaOH + HNO 3 Set 3: NH 3 + HCl Set 4: NaOH + CH 3 COO 2 H a. Four b. Three c. Two d. One e. Zero (none are acidic) 24. For the reaction: 2SO 2 (g) + O 2 (g) 2 SO 3 (g) ΔH = -198 kj Carried out at constant volume, the concentration of O 2 at equilibrium will increase if a. SO 2 is added to the system b. SO 3 is added to the system c. The temperature of the system is lowered. d. An inert gas is added to the system 25. A solution of sodium acetate is water is observed to become more alkaline (basic) as the temperature is raised. Which conclusion can be drawn? CH 3 COONa + H 2 O CH 3 COOH + -OH a. The forward reaction proceeds with an evolution of heat b. The forward reaction proceeds with an absorption of heat c. Acetic acid is less volatile than water d. Sodium acetate is less soluble in hot water than in cold water e. At higher temperature the reaction Na + + -OH will occur 26. Into an empty vessel COCl 2 (g) is introduced at 1.0 atm pressure whereupon it dissociates until equilibrium is established: 2COCl 2 (g) C(graphite) + CO 2 (g) + 2Cl 2 (g) If x represents the partial pressure of CO 2 (g) at equilibrium, what is the value of the equilibrium constant, K p? a. b. c. d. (x)2x 2 (1.0 2x) 2 x(x)(2x) x 2 x(2x) 2 (1.0 2x) 2 x(2x) 2 (1.0 x) 2

6 27. A buffer of ph 4.1 is to be prepared from a weak acid and its salt. The best acid from which to prepare the buffer is a. Phthalic acid, K 1 = (first ionization) b. Hydrogen phthalate, K 2 = (second ionization of phthalic acid) c. Benzoic acid, K = d. Hydrocyanic acid, K = The decomposition of phosphine, PH 3, follows first-order kinetics: 4 PH 3 (g) P 4 (g) + 6 H 2 (g) The half life for the reaction at 550 C is 81.3 seconds. How long does it take for the reaction to be 75.8% complete? a seconds b seconds c seconds d. 117 seconds e. 168 seconds 29. Which statement most accurately describes the behavior of a catalyst? a. A catalyst increases the ΔG of a reaction and hence the forward rate. b. A catalyst reduces the ΔH of a reaction and hence the temperature needed to produce products. c. A catalyst reduces the activation energy for a reaction and increases the rate of reaction d. A catalyst increases the equilibrium constant and final product concentrations 30. The rate expression for a second order reaction is a. Rate = k[a] b. Rate = k[a][b] c. Rate = k[a] 2 [B] d. Rate = k[a] 2 [B] Which of the following shows the greatest increase in disorder? a. NH 4 Br(s) NH 3 (g) + HBr(g) b. C 2 H 4 (g) + HBr(g) C 2 H 5 Br(g) c. CO 2 (s) CO 2 (g) d. C(s) + ½ O 2 (g) CO(g) e. C(graphite) + 2H 2 (g) CH 4 (g)

7 32. Consider the following reaction: 2Fe 2 O 3 (s) + 3C(s) 4Fe(s) + 3CO 2 (g) where ΔH r = 462 kj and ΔS r = 558 J/K, calculate the equilibrium constant for this reaction at 525 C. a b c d e Balance the following redox reaction which occurs in acidic conditions: Cu(s) + NO 3 - (aq) Cu 2+ (aq) + NO (g) a. 4H + + NO Cu (s) Cu 2+ + NO + 2H 2 O b. 2H 2 O + NO Cu (s) NO + Cu H + c. 2NO H + + 3Cu (s) 3Cu NO + 4H 2O d. 3NO H + + 2Cu (s) 2Cu 2+ + NO + 3H 2 O e. 6H + + 3NO Cu 2+ Cu (s) + NO + 3H 2 O 34. In every electrolytic and galvanic (voltaic) cell the anode is the electrode a. At which oxidation occurs. b. Which attracts cations. c. At which electrons are supplied to the solution d. At which reduction occurs. 35. Fill in the conjugate base for each acid. Then circle the weakest of the bases listed. Acid Conjugate base Ionization constant HCl 100% ionized H 2 SO H 2 S HS A 1.26 M Cu(NO 3 ) 2 solution has a density of 1.19 g/cm 3. What is the molality of this solution? a b c d The addition of a small amount of acid or base will have very little effect on the ph value of a solution containing equal molar concentrations of a. NH 4 Cl and NaCl b. NaOH and HCl c. NH 3 and NH 4 Cl d. NaOH and NaCl e. NH 3 and NaCl

8 38. Consider an equilibrium mixture of oxygen and ozone according to the equation 3 O 2 (g) 2 O 3 (g) The partial pressure of O 2 was measured in a flask at equilibrium as 1.25 atm and the total pressure in the flask was 1.75 atm. Calculate K p. Constant temperature was maintained. a b c d. 1.6 e At a specific temperature, the equilibrium constant for the following reaction is given. 2NO 2 (g) + O 2 (g) 2NO 3 (g) K c = 0.25 If 1.5 mol NO 2, 3.0 mol O 2 and 2.0 mol NO 3 are introduced into a 1.00 L flask, what changes in concentration (if any) will be observed as the system reaches equilibrium? a. [NO 2 ] increases; [O 2 ] increases; [NO 3 ] decreases b. [NO 2 ] increases; [O 2 ] decreases; [NO 3 ] decreases c. [NO 2 ] decreases; [O 2 ] decreases; [NO 3 ] increases d. [NO 2 ] decreases; [O 2 ] increases; [NO 3 ] increases e. All concentrations remain the same. 40. At the neutralization point of the titration of an acid with base, what condition is met? a. Volume of base added from buret equals volume of acid in reaction flask b. Molarity of base from the buret equals molarity of acid in reaction flask c. Moles of base added from the buret equals moles of acid in reaction flask d. % ionization of base added from the buret equals % ionization of the acid in flask e. All of the above conditions are met 41. A reaction was found to be second order in carbon monoxide concentration. What happens to the rate of the reaction if the concentration of carbon monoxide is doubled with everything else held constant? a. It doubles b. It remains unchanged c. It triples d. It increases by a factor of 4

9 42. Kinetic data for the following reaction was determined experimentally. 4NO 2 (g) + O 2 (g) 2N 2 O 5 (g) Experiment [NO 2 ] 0 (mol/l) [O 2 ] 0 (mol/l) Initial rate (mol/l) What is the rate law for this reaction? a. Rate = k[no 2 ] 4 [O 2 ] 1 b. Rate = k[no 2 ] 1/2 [O 2 ] 2 c. Rate = k[no 2 ] 2 [O 2 ] 2 d. Rate = k[no 2 ] 1 [O 2 ] 1 e. Rate = k[no 2 ] 1 [O 2 ] In basic solution, (CH 3 ) 3 CCl reacts according to the equation (CH 3 ) 3 CCl + -OH (CH 3 ) 3 COH + Cl- The accepted mechanism for the reaction is (CH 3 ) 3 CCl (CH 3 ) 3 C + + Cl- slow (CH 3 ) 3 C + + OH- (CH 3 ) 3 OH fast What is the rate law expression for the reaction? a. Rate = k[(ch 3 ) 3 C + ] 2 [-OH] 1 b. Rate = k[(ch 3 ) 3 C + ][-OH] 2 c. Rate = k[cl-] d. Rate = k[(ch 3 ) 3 CCl] e. Rate = k[(ch 3 ) 3 CCl][-OH] The Arrhenius equation, k = Ae -E/RT expresses the relationship between the reaction rate constant, k, and the energy of activation, E. The probability that colliding molecules will react a. Increases with increasing energy of activation. b. Depends only on the empirical constant, A. c. Increases with decreasing temperature. d. Decreases with increasing energy of activation. 45. The value of the rate constant of a reaction can generally be expected to a. Be independent of temperature b. Increase with increasing temperature c. Decrease with increasing temperature d. Decrease with increasing temperature only if the reaction is exothermic

10 46. Use the data in the following table to calculate the equilibrium constant for the reaction of lime with water at 298 K. CaO (s) + H 2 O (l) Ca(OH) 2 (s) Compound ΔG f (kj/mol) CaO (s) -604 H 2 O (l) -237 Ca(OH) 2 (s) -899 a b c d e Which change is likely to be accompanied by the greatest increase in entropy? a. N 2 (g) + 3H 2 (g) 2NH 3 (g) (at 25 C) b. Ag + (aq) + Cl- (aq) AgCl (s) (at 25 C) c. CO 2 (s) CO 2 (g) (at -70 C) d. H 2 O (g) H 2 O (l) (at 100 C) 48. A particular chemical reaction has a negative ΔH and negative ΔS. Which statement is correct? a. The reaction is spontaneous at all temperatures. b. The reaction is nonspontaneous at all temperatures. c. The reaction becomes spontaneous as temperature increases. d. The reaction becomes spontaneous as temperature decreases. 49. At 298 K the equilibrium constant for H 2 (g) + ½ O 2 (g) H 2 O (l) Compound and state ΔG f (kj/mol) H 2 O (l) -237 H 2 O (g) -229 a. Is larger than the K eq for H 2 (g) + ½ O 2 (g) H 2 O (g) b. Will have a value of 1.0 at equilibrium c. Cannot be computed since data on O 2 and H 2 are not provided d. Is smaller than the K eq for H 2 (g) + ½ O 2 (g) H 2 O (g) 50. Given the two half reactions and their potentials, which net reaction is not spontaneous? Zn 2+ (aq) + 2e- Zn (s) E = V Ni 2+ (aq) + 2e- Ni (s) E = V a. Ni 2+ (aq) + Zn 2+ (aq) Ni (s) + Zn (s) b. Ni 2+ (aq) + Zn (s) Ni (s) + Zn 2+ (aq) c. Ni (s) + Zn 2+ (aq) Zn (s) + Ni 2+ (aq) d. Zn (s) + Ni (s) Ni 2+ (aq) + Zn 2+ (aq) e. Zn (s) + Zn 2+ (aq) Ni 2+ (aq) + Ni (s)

11 51. During the electrolysis of an aqueous solution of CuSO 4 with inert electrodes a. The anode loses mass and the cathode gains mass. b. The mass of the anode remains the same but the cathode gains mass c. The mass of the anode decreases but the mass of the cathode remains constant d. The anode and the cathode neither gain nor lose mass e. Both electrodes gain in mass 52. In the titration of 50.0 ml of benzoic acid with 50.0 ml of M NaOH, the properties of the solution at the equivalence point will correspond exactly to the properties of a. A M sodium benzoate solution b. A M sodium hydroxide solution c. A M benzoic acid solution d. A M sodium benzoate solution 53. Calcium carbonate decomposes when heated according to the following reaction: CaCO 3 (s) CaO (s) + CO 2 (g) The mass of the CaCO 3 could be increased by a. Adding more CO 2 b. Decreasing the volume of the container c. Removing some CaO d. Increasing the temperature e. Both A and B 54. Use the data in the following table to calculate the free energy change for the reaction at 25 C. ½ N 2 (g) + 3/2 H 2 (g) NH 3 (g) a kj b kj c kj d kj e kj Compound ΔS (J/mol K) ΔH (kj/mol) N 2 (g) NH 3 (g) H 2 (g) When Al 2O 3 (s) is formed from the elements at standard condition, the values of ΔH and ΔG at 298 K are kj/mol and kj/mol, respectively. The standard entropy of formation per mole, in joules per degree, will be a b c d e. 15.7

12 56. What is the consequence of heating this equilibrium system at constant pressure? 2SO 2 (g) + O 2 (g) 2SO 3 (g) ΔH = -198 kj a. The concentration of SO 3 will decrease b. The partial pressure of SO 2 will decrease c. The equilibrium constant will increase d. The total volume of the system will decrease 57. Calculate ΔG for the following reaction at 298 K Ag(NH 3 ) 2+ (aq, 0.400M) Ag + (aq, M) + 2NH 3 (aq, M) ΔG = kj a kj b kj c kj d kj e kj 58. The value of E for the following reaction is 0.63V. What is the value of E for this reaction when the concentration of Zn 2+ is M and the concentration of Pb 2+ is 1.0 M? Pb 2+ (aq) + Zn (s) Zn 2+ (aq) + Pb (s) a V b V c V d V **Use the data on the table provided to answer the next three questions. 59. Predict the products at the cathode when electric current is passed through a solution of KI. a. K (s) b. H 2 (g) c. I 2 (l) d. O 2 (g) e. H 2 O (l) 60. Calculate the E for the following reaction: F - (aq) + Cl 2 (g) F 2 (g) + 2Cl - (aq) a V b V c V d V e V 61. Which of the following is the best reducing agent? a. Ag + b. Al c. F d. Zn 2+ e. F 2