Chemistry 2

Practice Final Exam

1. When white phosphorous P4 is exposed to O2, the white solid will burst into flame and release a large amount of heat. Which of the following is TRUE about the equilibrium constant, K, for the reaction?
2. P4(s) + 5 O2(g) P4O10(s)

(a) K << 1
(b) K = 0
(c) K = 1
(d) K >> 1

3. If the reaction quotient, Q, is greater than Kc for a process, then the process is
4. (a) at equilibrium.
(b) to the right (product side) of the point of equilibrium.
(c) to the left (reactant side) of the point of equilibrium.
(d) can't tell from the available information.
(e) either b or c.

5. Calculate Kc for Reaction III below, using the following data.
6. Reaction I: 2 NO2(g) 2 NO(g) + O2(g) Kc = 1.81 x 10-14

Reaction II: 2 NO(g) N2(g) + O2(g) Kc = 9.71 x 1017

Reaction III: 2 NO2(g) N2(g) + 2 O2(g) Kc = ?

(a) Kc = 1.86 x 10-32
(b) Kc = 5.69 x 10-5
(c) Kc = 7.18 x 102
(d) Kc = 1.76 x 104
(e) Kc = 5.36 x 1031

7. The equilibrium concentration of CH3OH at a given temperature is 0.20 M. What is the value of Kc for this reaction at this temperature? Initial concentrations are: [CO] = 2.0 M, [H2] = 0.50 M
8. CO + 2 H2 CH3OH

(a) Kc = 0.09
(b) Kc = 0.90
(c) Kc = 1.00
(d) Kc = 1.11
(e) Kc = 11.1

9. Which manipulation(s) will shift the direction of equilibrium toward increased production of products? The reaction is exothermic (DHrxn < 0).
10. CO2(g) + H2(g) CO(g) + H2O(g)

(1) increasing the concentration of H2
(2) decreasing the reaction temperature
(3) increasing the reaction pressure
(4) removing H2O from the system
(5) increasing the concentrations of H2 and CO2

(a) 1, 2, 3, 4, 5
(b) 1, 4, 5
(c) 1, 3, 4, 5
(d) 1, 2, 4, 5
(e) 3 only

11. At 700 °C, Kc = 416 for the reaction:
12. 2 SO2 + O2 2 SO3

Calculate the value of Kc at 700 °C for the reaction:

2 SO3 2 SO2 + O2

(a) Kc = 4.81 x 10-3
(b) Kc = 2.40 x 10-3
(c) Kc = 2.08 x 102
(d) Kc = 4.16 x 102
(e) Kc = 8.32 x 102

13. Which of the following when dissolved in water will yield a slightly acidic solution?
14. (a) NH3
(b) NH4Cl
(c) NaNO3
(d) Na2CO3
(e) Mg(NO3)2

15. The pH of 0.1 M HNO3 is:
16. (a) -0.1
(b) -1
(c) 0.1
(d) 1
(e) 2

17. Which of the following is arranged in order of increasing acid strength (weakest acid first and strongest acid last)?
18. (a) CH4 < H2O < NH3 < HCl
(b) HCl < H2O < NH3 < CH4
(c) HCl < NH3 < H2O < CH4
(d) CH4 < NH3 < H2O < HCl
(e) NH3 < CH4 < H2O < HCl

19. What is the value of Ka for citric acid (the sour flavor of lemon) if 8.7% of the citric acid molecules in a 0.100 M solution dissociate ?
20. (a) Ka = 8
(b) Ka = 9 x 10-2
(c) Ka = 9 x 10-3
(d) Ka = 8 x 10-3
(e) Ka = 8 x 10-4

21. What is the pH of a 0.1 M solution of sodium acetate, NaOAc ?
Ka of acetic acid, HOAc, is 1.8 x 10-5 ?
22. (a) pH = 2.9
(b) pH = 3.7
(c) pH = 5.1
(d) pH = 8.9
(e) pH = 9.3

23. Which of the following solutions is an acidic buffer?
24.  Acid pKa Ka HCO2H 3.75 1.8 x 10-4 H2S 7.00 1.0 x 10-7 H2PO4- 7.20 6.3 x 10-8 HCN 9.22 6.0 x 10-10 NH4+ 9.24 5.6 x 10-10

(a) 0.10 M H2S and 0.10 M NaHS
(b) 0.10 M NH4Cl and 0.10 M NH3
(c) 0.10 M HCN and 0.10 M NaCN
(d) 0.10 M HCO2H and 0.10 M NaHCO2
(e) 0.10 M NaH2PO4 and 0.10 M Na2HPO4

25. How long will current flow if a Pb storage battery uses 500 g of Pb to delivers
1.50 amps ?
26. Pb(s) + SO42-(aq) PbSO4(s) + 2 e¯

(a) 8.34 hours
(b) 21.6 hours
(c) 43.1 hours
(d) 86.2 hours
(e) 194 hours

27. What is the sum of the coefficients of all REACTANTS when the unbalanced reaction below is balanced in an acidic solution ?
28. S2O32-(aq) + MnO4-(aq) SO42-(aq) + Mn2+(aq)

(a) 9
(b) 13
(c) 18
(d) 25
(e) 27

29. Which statement(s) best describes what occurs when molten NaCl undergoes electrolysis?
30. I. Cl2(g) is produced at the anode.
II. Na metal is produced at the cathode.
III. The reaction generates a current spontaneously.

(a) I & II
(b) I & III
(c) II & III
(d) I, II & III
(e) III only

31. What is the rxn for the reaction below?
32. 2 Fe(s) + O2(g) + 2 H2O(l) 2 Fe2+(aq) + 4 OH-(aq)

(a) - 0.48 V
(b) - 0.04 V
(c) + 0.78 V
(d) + 0.84 V
(e) + 1.28 V

33. Using the standard reduction potentials (on the last page) which statement is TRUE?
34. (a) Cu(s) can reduce Ni2+(aq) to Ni(s).
(b) H2(g) can reduce Ni2+(aq) to Ni(s).
(c) H2(g) can reduce Na+(aq) to Na(s).
(d) Hg(l) can reduce Au3+(aq) to Au(s).
(e) Hg(l) can reduce Sn4+(aq) to Sn2+(aq).

35. A clean iron nail is left outside in water. After a time, rust, Fe2O3 · 3 H2O, forms according to the overall reaction below. Which statement about this process is TRUE ?
36. 4 Fe(s) + 3 O2(aq) + 6 H2O(l) 2 Fe2O3 · 3 H2O(s)

(a) Fe is oxidized by the O2.
(b) Fe is oxidized by the H2O.
(c) O2 is oxidized by the Fe.
(d) O2 is reduced by the H2O.
(e) This is not an oxidation-reduction reaction.

37. Which process has a POSITIVE S°?
38. I. 4 Al(s) + 3 O2(g) 2 Al2O3(s)

II. C6H12O6(s) + 6 O2(g) 6 CO2(g) + 6 H2O(g)

III. 8 H2S(g) + 4 O2(g) S8(s) + 8 H2O(l)

(a) I & II
(b) I & III
(c) II & III
(d) I, II, & III
(e) II only

39. What is S° for the reaction below?
40. P4O10(s) + 6 H2O(l) 4 H3PO4(aq)

 Compound S°ac J/(K·mol) H2O(l) - 321 H3PO4(aq) - 1374 P4O10(s) - 2034

(a) - 3141 J/(K·mol)
(b) - 1536 J/(K·mol)
(c) - 981 J/(K·mol)
(d) + 981 J/(K·mol)
(e) + 2586 J/(K·mol)

41. The third law of thermodynamics defines zero on the entropy scale. Entropy is equal to zero for a perfectly ordered crystal when ...
42. (a) T = 0 K
(b) T = 25 °C
(c) P = 1 atm
(d) Concentration = 1 M
(e) T = 25 °C, P = 1 atm, Concentration = 1 M

43. From the ac and ac values, determine what is the driving force(s) behind the reaction below.
44. Fe2O3(s) + 2 Al(s) Al2O3(s) + 2 Fe(s)

 Compound H°ac kJ/mol S°ac J/(K·mol) Al(s) - 326 - 136 Al2O3(s) - 3076 - 761 Fe(s) - 416 - 153 Fe2O3(s) - 2404 - 757

(a) Entropy
(b) Enthalpy
(c) Le Châtelier principle
(d) Enthalpy and Entropy
(e) Enthaply, Entropy, and Le Châtelier principle

45. Determine the temperature at which CH3OH boils according to the reaction below. (Boiling point is the temperature at which this process reaches equilibrium at 1 atm of pressure.)
46. CH3OH(l) CH3OH(g)
H° = + 38 kJ/mol
= + 113 J/(K·mol)

(a) 0.34 K
(b) 3.0 K
(c) 150 K
(d) 340 K
(e) 3000 K

47. What is rxn for the dissociation of hydrofluoric acid in H2O at 298 K if
Ka = 7.2 x 10-4 ?
48. HF(aq) + H2O(l) H3O+(aq) + F-(aq)

(a) + 6.3 kJ/mol
(b) + 7.8 kJ/mol
(c) + 18 kJ/mol
(d) + 29 kJ/mol
(e) + 177 kJ/mol

49. The reaction show below is second-order in NO and first-order in H2.
50. 2 NO(g) + 2 H2(g) N2(g) + 2 H2O(g)

Rate = k [NO]2 [H2]1

A possible mechanism for this reaction is given below. Assuming this mechanism is correct, which is the SLOW step ?

step 1: 2 NO(g) N2O2(g)

step 2: N2O2(g) + H2(g) N2O(g) + H2O(g)

step 3: N2O(g) + H2(g) N2(g) + H2O(g)

(a) step 1
(b) step 2
(c) step 3
(d) all of the above

51. Use the data below to determine the rate law for the reaction between nitrogen oxide and chlorine to form nitrosyl chloride.
52. 2NO(g) + Cl2(g) 2 NOCl(g)

 Initial [NO], M Initial [Cl2], M Initial Reaction Rate, M/s 0.10 0.10 0.117 0.20 0.10 0.468 0.30 0.10 1.054 0.30 0.20 2.107

(a) Rate = k [NO]1/2 [Cl2]
(b) Rate = k [NO] [Cl2]
1/2
(c) Rate = k [NO] [Cl2]
(d) Rate = k [NO] [Cl2]2
(e) Rate = k [NO]2 [Cl2]

53. Use the results of the previous problem to determine the rate constant, k, for this reaction.
54. (a) k = 11.7 s-1
(b) k = 117 M-2 s-1
(c) k = 3.70 M
1/2 s-1
(d) k = 0.272 M
1/2 s-1
(e) k = 8.55 x 10-3 M-2 s-1

55. 14C decays to 12C with a first-order half life (t1/2) of 5730 years. What is the rate constant, k, for the reaction in year-1?
56. (a) k = 1.0 x 105 year-1
(b) k = 1.9 x 104 year-1
(c) k = 4.0 x 103 year-1
(d) k = 5.3 x 10-5 year-1
(e) k = 1.2 x 10-4 year-1

57. Charcoal samples from Stonehenge in England show 62.3% of the carbon-14 activity found in living tissue. How old are these charcoal samples?
(Use the t
1/2 or the calculated k from the previous problem for the 14C decay.)
58. (a) 170 years old
(b) 1700 years old
(c) 3900 years old
(d) 8100 years old
(e) 17000 years old

59. Assume that the activation energy was measured for both the forward (Ea = 185 kJ/molrxn) and reverse (Ea = 120 kJ/molrxn) directions of a reversible reaction. A catalyst decreases the activation energy for the forward reaction to
90 kJ/molrxn. What would be the activation energy for the catalyzed REVERSE reaction ?

(a) Ea = 25 kJ/molrxn
(b) Ea = 30 kJ/molrxn
(c) Ea = 95 kJ/molrxn
(d) Ea = 155 kJ/molrxn
(e) Ea = 215 kJ/molrxn

IMPORTANT CONSTANTS :

 Gas constant R = 0.0821 L·atm/(K·mol) R = 8.314 J/(K·mol) Faraday's constant F = 96,500 C / 1 mol of e¯ 1 C = 1 A·sec Temperature K = °C + 273 Water ionization Kw = 1 x 10-14

STANDARD REDUCTION POTENTIALS red (V)

 Na+(aq) + e¯ Na(s) - 2.71 V Mg2+(aq) + 2 e¯ Mg(s) - 2.37 V Zn2+(aq) + 2 e¯ Zn(s) - 0.76 V Fe2+(aq) + 2 e¯ Fe(s) - 0.44 V Ni2+(aq) + 2 e¯ Ni(s) - 0.25 V 2 H+(aq) + 2 e¯ H2(g) 0.00 V Sn4+(aq) + 2 e¯ Sn2+(aq) + 0.13 V Cu2+(aq) + 2 e¯ Cu(s) + 0.34 V O2(g) + 2 H2O(l) + 4 e¯ 4 OH-(aq) + 0.40 V I2(s) + 2 e¯ 2 I-(aq) + 0.54 V Hg2+(aq) + 2 e¯ Hg(l) + 0.86 V Br2(l) + 2 e¯ 2 Br-(aq) + 1.07 V Au3+(aq) + 3 e¯ Au(s) + 1.50 V