Unit 19 Study Guide

Unit 19 Study Guide

1. For which process is S negative?A) evaporation of 1 mol of CCl4(l)B) mixing 5 mL ethanol with 25 mL waterC) compressing 1 mol Ne at constant temperature from 1.5 atm to 0.5 atmD) raising the temperature of 100 g Cu from 275 K to 295 KE) grinding a large crystal of KCl to powder

2. In which reaction is S° expected to be positive?A) I2(g) I2(s)B) H2O(1) H2O(s)C) CH3OH(g) + (3/2)O2(g) CO2(g) + 2H2O(l)D) 2O2(g) + 2SO(g) 2SO3(g)E) none of these

3. Which statement is true?A) All real processes are irreversible.B) A thermodynamically reversible process takes place infinitely fast.C) In a reversible process, the state functions of the system are always much greater than those of the surroundings.D) There is always more heat given off to the surroundings in a reversible process than in an unharnessed one.E) All statements (a–d) are true.

4. A 100-mL sample of water is placed in a coffee cup calorimeter. When 1.0 g of an ionic solid is added, the temperature decreases from 21.5°C to 20.8°C as the solid dissolves. For the dissolving of the solid

A) H < 0B) Suniv > 0C) Ssys< 0D) Ssurr > 0E) none of these

5. Which of the following result(s) in an increase in the entropy of the system?

I. (See diagram above.)II. Br2(g) Br2(l)

III .NaBr(s) Na+(aq) + Br–(aq)O2(298 K) O2(373 K)

V. NH3(1 atm, 298 K) NH3(3 atm, 298 K)

A) IB) II, VC) I, III, IVD) I, II, III, IVE) I, II, III, V

6. A mixture of hydrogen and chlorine remains unreacted until it is exposed to ultraviolet light from a burning magnesium strip. Then the following reaction occurs very rapidly:H2(g) + Cl2(g) 2HCl(g) G = –45.54 kJ

H = –44.12 kJS = –4.76 J/K

A) The reactants are thermodynamically more stable than the products.B) The reaction has a small equilibrium constant.C) The ultraviolet light raises the temperature of the system and makes the reaction more favorable.D) The negative value for S slows down the reaction.E) The reaction is spontaneous, but the reactants are kinetically stable.

7. Ten identical coins are shaken vigorously in a cup and then poured out onto a table top. Which of the following distributions has the highest probability of occurrence? (T = Tails, H = Heads)

A) T10H0

B) T8H2

C) T7H3

D) T5H5

E) T4H6

8. Which statement below is not upheld by the second law of thermodynamics?

A) The change of entropy of the universe is always positive.B) The entropy of a perfect crystal at 0 K is zero.C) Machines always waste some energy.D) A machine is never 100% efficient.E) All of these

9. If two pyramid-shaped dice (with numbers 1 through 4 on the sides) were tossed, which outcome has the highest entropy?

A) The sum of the dice is 3.B) The sum of the dice is 4.C) The sum of the dice is 5.D) The sum of the dice is 6.E) The sum of the dice is 7.

10. A two-bulbed flask contains 3 particles. What is the probability of finding all 3 particles on the left side? (Ignore significant figures for this problem.)

A) 1.50 %B) 1.73 %C) 12.50 %D) 0.33 %

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E) 25.00 %

11. Which of the following shows a decrease in entropy?A) precipitationB) gaseous reactants forming a liquidC) a burning piece of woodD) melting iceE) two of these

12. A chemical reaction is most likely to be spontaneous if it is accompanied by

A) increasing energy and increasing entropy.B) lowering energy and increasing entropy.C) increasing energy and decreasing entropy.D) lowering energy and decreasing entropy.E) None of these (a-d)

13. For the dissociation reaction of the acid HF HF(aq) H+(aq) + F–(aq) S is observed to be negative. The best

explanation is:A) This is the expected result since each HF molecule produces two ions when it dissociates.B) Hydration of the ions produces the negative value of S.C) The reaction is expected to be exothermic and thus S should be negative.D) The reaction is expected to be endothermic and thus S should be negative.E) None of these can explain the negative value of S.

14. The second law of thermodynamics states thatA) the entropy of a perfect crystal is zero at 0 K.B) the entropy of the universe is constant.C) the energy of the universe is increasing.D) the entropy of the universe is increasing.E) the energy of the universe is constant.

15. Which of the following statements is (are) always true?In order for a process to be spontaneous, the entropy of the universe must increase.

II. A system cannot have both energy disorder and positional disorder.

III. Suniv =

IV. S° is zero for elements in their standard states.

A) IB) I, IVC) I, III, IVD) II, IVE) II

16. Which of the following statements is always true for a spontaneous process?I. Ssys > 0

II .Ssurr > 0

III .Suniv > 0

IV. Gsys > 0

A) IB) IIIC) IVD) I and IIIE) III and IV

17. Assume that the enthalpy of fusion of ice is 6020 J/mol and does not vary appreciably over the temperature range 270-290 K. If one mole of ice at 0oC is melted by heat supplied from surroundings at 272 K, what is the entropy change in the surroundings, in J/K?

A) 22.6B) 22.1C) 0.0D) –22.1E) –22.6

18. If the change in entropy of the surroundings for a process at 431 K and constant pressure is -326 J/K, what is the heat flow absorbed by for the system?

A) 326 kJB) 1.32 kJC) –141 kJD) 105 kJE) 141 kJ

19. The heat of vaporization for 1.0 mole of water at 100.oC and 1.0 atm is 40.60 kJ/mol. Calculate ΔS for the

process at 100.oC.A) 109 J/K molB) –109 J/K molC) 406 J/K molD) –406 J/K molE) none of these

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20. A change of state that occurs in a system is accompanied by 61.7 kJ of heat, which is transferred to the surroundings at a constant pressure and a constant temperature of 300. K. For this process ΔSsurr is:

A) 61.7 kJB) –61.7 kJC) –206 J/KD) 206 J/KE) 238 kJ

21. For a spontaneous exothermic process, which of the following must be true?

A) G must be positive.B) S must be positive.C) S must be negative.D) Two of the above must be true.E) None of the above (a-c) must be true.

22. The enthalpy of vaporization of ethanol is 38.73 kJ/mol at its boiling point (78oC). Calculate the value of ΔSsurr

when 1.00 mole of ethanol is vaporized at 78oC and 1.00 atm.A) 0B) 4.97e2 J/K molC) 1.10e2 J/K molD) –1.10e2 J/K molE) –4.97e2 J/K mol

23. The enthalpy of vaporization of ethanol is 38.71 kJ/mol at its boiling point (78oC). Calculate the value of ΔS when 1.00 mole of ethanol is vaporized at 78oC and 1.00 atm.

A) 0B) 4.96e2 J/K molC) 1.10e2 J/K molD) –1.10e2 J/K molE) –4.96e2 J/K mol

24. Ssurr is _______ for exothermic reactions and ______ for endothermic reactions.

A) favorable, unfavorableB) unfavorable, favorableC) favorable, favorableD) unfavorable, unfavorableE) cannot tell

25. S is _______ for exothermic reactions and ______ for endothermic reactions.

A) favorable, unfavorableB) unfavorable, favorableC) favorable, favorableD) unfavorable, unfavorableE) cannot tell

26. For the vaporization of a liquid at a given pressure: (Note: Answers c and d imply that G is zero at some temperature.)

A) G is positive at all temperatures.B) G is negative at all temperatures.C) G is positive at low temperatures, but negative at high temperatures.D) G is negative at low temperatures, but positive at high temperatures.

E) None of these (a-d)

27. For a particular chemical reaction H = 5.5 kJ and S = –25 J/K Under what temperature condition is the reaction spontaneous?

A) When T < –220 K.B) When T < 220 K.C) The reaction is spontaneous at all temperatures.D) The reaction is not spontaneous at any temperature.E) When T > 220 K.

Use the following to answer questions 28-30: The following questions refer to the following reaction at constant 25°C and 1 atm.

2Fe(s) + (3/2)O2(g) + 3H2O(l) 2Fe(OH)3(s) H = kJ/molSubstance S° (J/mol K)Fe(OH)3(s) 107Fe(s) 27O2(g) 205H2O(l) 70

28. Determine Ssurr for the reaction (in kJ/mol K)A) 3.14B) 0.937C) 0.378D) 1.31E) 2.65

29. Determine Suniv for the reaction (in kJ/mol K)A) 0.22B) 2.2C) 0.36D) 2.8E) 3.6

30. What must be true about G for this reaction?A) G = HB) G = 0C) G > 0D) G < 0E) G = Suniv

31. Which of the following is true for exothermic processes?

A) Ssurr < 0B) Ssurr = –H/TC) Ssurr = 0D) Ssurr > 0E) two of these

32. For the reaction A + B C + D, H° = +40 kJ and S° = +50 J/K. Therefore, the reaction under standard conditions is

A) spontaneous at temperatures less than 10 K.B) spontaneous at temperatures greater than 800 K.C) spontaneous only at temperatures between 10 K and 800 K.D) spontaneous at all temperatures.E) nonspontaneous at all temperatures.

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33. In which case must a reaction be spontaneous at all temperatures?

A) H is positive, S is positive.B) H = 0, S is negative.C) S = 0, H is positive.D) H is negative, S is positive.E) none of these

34. Consider the dissociation of hydrogen: H2(g) 2H(g)One would expect that this reaction:

A) will be spontaneous at any temperature.B) will be spontaneous at high temperatures.C) will be spontaneous at low temperatures.D) will not be spontaneous at any temperature.E) will never happen.

35. For the process ΔHo = 9.21 kJ/mol and ΔSo = 43.9 J/mol/K. What is the melting point of chloroform?

A) –63oCB) 210.oCC) 131oCD) 63oCE) –131

36. For the process S8 (rhombic) S8 (monoclinic) at 110°C, H = 3.21 kJ/mol and S = 8.70 J/K mol (at 110°C).Which of the following is correct?

A) This reaction is spontaneous at 110°C (S8

(monoclinic) is stable).B) This reaction is spontaneous at 110°C (S8

(rhombic) is stable).C) This reaction is nonspontaneous at 110°C (S8 (rhombic) is stable).D) This reaction is nonspontaneous at 110°C (S8 (monoclinic) is stable).E) Need more data.

37. As O2(l) is cooled at 1 atm, it freezes at 54.5 K to form Solid I. At a lower temperature, Solid I rearranges to Solid II, which has a different crystal structure. Thermal measurements show that ΔH for the I II phase transition is -743.08 J/mol, and ΔS for the same transition is -17.0 J/K mol. At what temperature are Solids I and II in equilibrium?

A) 13.6 KB) 43.7 KC) 19.8 KD) 98.2 KE) They can never be in equilibrium because they are both solids.

38. At constant pressure, the following reaction 2NO2(g) N2O4(g) is exothermic. The reaction (as written) is

A) always spontaneous.B) spontaneous at low temperatures, but not high temperatures.

C) spontaneous at high temperatures, but not low temperatures.D) never spontaneous.E) Cannot tell.

Use the following to answer questions 39-41: At 1 atm, liquid water is heated above 100°C.

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39. Ssurr for this process isA) greater than zero.B) less than zero.C) equal to zero.D) More information is needed to answer this question.E) None of these (a-d)

40. S for this process isA) greater than zero.B) less than zero.C) equal to zero.D) More information is needed to answer this question.E) None of these (a-d)

41. Suniv for this process isA) greater than zero.B) less than zero.C) equal to zero.D) More information is needed to answer this question.E) None of these (a-d)

42. Given the following data (ΔHf, So, respectively) for N2O4(l) -20. kJ/mol, 209.0 J/K mol, and N2O4(g) 10. kJ/mol, 304.3 J/K mol. Above what temperature (in oC) is the vaporization of N2O4 liquid spontaneous? (Ignore significant figures for this problem.)

A) Above –178oC.B) Above –231oC.C) Above 3oC.D) Above 30.oC.E) Above 42oC.

43. Given that ΔHvap is 54.3 kJ/mol, and the boiling point is 83.4oC, 1 atm, if one mole of this substance is vaporized at 1 atm, calculate ΔSsurr.

A) –152 J/K molB) 152 J/K molC) 651 J/K molD) –651 J/K molE) 0

44. Given that ΔHvap is 58.1 kJ/mol, and the boiling point is 83.4oC, 1 atm, if one mole of this substance is vaporized at 1 atm, calculate ΔS.


45. Given that ΔHvap is 58.2 kJ/mol, and the boiling point is 83.4oC, 1 atm, if one mole of this substance is vaporized at 1 atm, calculate ΔG.


46. As long as the disorder of the surroundings is increasing, a process will be spontaneous.

47. For a given process, Ssurr and Ssys have opposite signs.

48. If Ssurr = –Ssys, the process is at equilibrium.

49. H° is zero for a chemical reaction at constant temperature.

50. The melting point of water is 0°C at 1 atm pressure because under these conditions

A) S for the process H2O(s) H2O(l) is positive.B) S and Ssurr for the process H2O(s) H2O(l) are both positive.C) S and Ssurr for the process H2O(s) H2O(l) are equal in magnitude and opposite in sign.D) G is positive for the process H2O(s) H2O(l).E) None of these is correct.

51. Substance X has a heat of vaporization of 57.0 kJ/mol at its normal boiling point (423oC). For the process X (l) X (g) at 1 atm and 423oC calculate the value of ΔSuniv.

A) 0B) 81.9 J/K molC) 135 J/K molD) –81.9 J/K molE) –135 J/K mol

52. Substance X has a heat of vaporization of 40.4 kJ/mol at its normal boiling point (423oC). For the process X (l) X (g) at 1 atm and 423oC calculate the value of ΔSSURR.


53. Substance X has a heat of vaporization of 50.6 kJ/mol at its normal boiling point (423oC). For the process X (l) X (g) at 1 atm and 423oC calculate the value of ΔS.


54. Substance X has a heat of vaporization of 43.5 kJ/mol at its normal boiling point (423oC). For the process X (l) X (g) at 1 atm and 423oC calculate the value of ΔG.


55. For a certain process at 355 K, ΔG = -10.3 kJ and ΔH = -9.2 kJ. Therefore, ΔS for the process is

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A) 0B) 3.1 J/K molC) –3.1 J/K molD) –25.9 J/K molE) 25.9 J/K mol

56. Consider the freezing of liquid water at –10°C. For this process what are the signs for H, S, and G?

H S G

A) + – 0B) + – 0C) – + 0D) – + –E) – – –

57. When a stable diatomic molecule spontaneously forms from its atoms, what are the signs of H°, S°, and G°?

H S G

A) + + +B) + – –C) + + +D) – – +E) – – –

58. Elemental sulfur exists in two crystalline forms, rhombic and monoclinic. From the following data, calculate the equilibrium temperature at which monoclinic sulfur and rhombic sulfur are in equilibrium.

ΔHfo (kJ/mol) So (J/K mol)

S (rhombic) 0S (monoclinic) 0.30

A) 448 KB) 201 KC) –201 KD) –448 KE) 0 K

59. The reaction 2H2O(g) 2H2(g) + O2(g) has a positive value of G°. Which of the following statements must be true?

A) The reaction is slow.B) The reaction will not occur. [When H2O(g) is introduced into a flask, no O2 or H2 will form even over a long period of time.]C) The reaction is exothermic.D) The equilibrium lies far to the right.E) None of these is true.

60. For the process of a certain liquid vaporizing at 1

atm, = 64.7 kJ/mol and = 74.1 J/mol K. Assuming these values are independent of T, what is the normal boiling point of this liquid? (Ignore significant figures for this problem.)

A) 873oCB) 1146oC

C) 600oCD) 0.873oCE) none of these

61. Consider the following processes:I. Condensation of a liquid..II Increasing the volume of 1.0 mol of an ideal gas at constant temperature..III. Dissolving an ionic solid in water..IV. Heating 1.0 mol of an ideal gas at constant volume..For how many of these is S positive?

A) 0B) 1C) 2D) 3E) 4

62. The third law of thermodynamics statesA) the entropy of the universe is increasing.B) the entropy of the universe is constant.C) the entropy is zero at 0 K for a perfect crystal.D) the absolute entropy of a substance decreases with increasing temperature.E) the entropy of the universe equals the sum of the entropy of system and surroundings.

63. Which of the following is not a state function?A) qB) GC) HD) EE) P

64. The standard free energy of formation of AgCl(s) is -109.6 kJ/mol. ΔGo for the reaction

is:A) 109.6 kJB) 219.2 kJC) –109.6 kJD) –219.2 kJE) none of these

65. Given the following free energies of formation:ΔGf

o

C2H2(g) 209.2 kJ/molC2H6(g) -32.94 kJ/mol

calculate Kp at 298 K for

A) 97.7B) 1.10C) 7.88e30D) 2.78e42E) None of these is within a factor of 10 of the correct answer.

66. Given the following data, calculate the normal boiling point for formic acid (HCOOH).

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(kJ/mol) (J/mol K)HCOOH(l) -410. 130.0HCOOH(g) -363 251.1

A) 0.39oCB) 388oCC) 661oCD) 279oCE) 115oC

67. Consider the following hypothetical reaction at 310 K. Standard free energies of formation are given in parentheses.

B ----------> C = -44.0 kJ/mol (?) (176.4 kJ/mol)Calculate the standard free energy of formation of compound B.

A) 220.4 kJ/molB) –220.4 kJ/molC) 132.4 kJ/molD) –132.4 kJ/molE) none of these

68. The acid dissociation constant for a weak acid HX at 25oC is 1.58e–8. Calculate the free energy of formation for X-

(aq) at 25oC. The standard free energies of HX(aq) and H+(aq) at 25oC are -211.5 kJ/mol and 0, respectively.

A) –208 kJ/molB) 256 kJ/molC) 0D) –167 kJ/molE) –256 kJ/mol

69. The standard molar free energies of formation of NO2(g) and N2O4(g) at 25oC are 51.840 and 99.936 kJ/mol, respectively. What is the value of Kp (in atm) for the reaction written as follows at 25oC?

A) 6.65e7B) 1.00C) 4.53D) 2.03e–36E) 3.71e–9

70. For the reaction

= 126.4 kJ/mol and = -74.9 J/K mol. At

368oC, equalsA) 154.0 kJ/molB) 48.1 kJ/molC) 174.4 kJ/molD) 78.4 kJ/mol

E) 155.9 kJ/mol

71. Given that for NH3 = -16.671 kJ/mol, calculate the equilibrium constant for the following reaction at 298 K:

A) 6.99e5B) 8.36e2C) 1.01D) 4.64e69E) 5.85e8

72. The following reaction takes place at 120°C: H2O(l) H2O(g) H = 44.0 kJ/mol S = 0.119 kJ/mol KWhich of the following must be true?

A) The reaction is not spontaneous.B) The reaction is spontaneous.C) G = 0D) G < 0E) two of these

73. Determine for the following reaction:

Substance (kJ/mol)CH4(g) -50.69O2(g) 0CO2(g) -394.4H2O(l) -237.4

A) –581.1 kJB) –919.9 kJC) –818.5 kJD) –682.5 kJE) 131.1 kJ

74. The question below refers to the following:When ignited, solid ammonium dichromate decomposes in a fiery display. This is the reaction for a "volcano" demonstration. The decomposition produces nitrogen gas, water vapor, and chromium(III) oxide. The temperature is constant at 25oC.

Substance (kJ/mol) (kJ/mol K)

-1140. 0.08117

-242 0.1187

0 0.1915

-22.5 0.1137

Determine reaction (in kJ/mol K).A) 0.2777B) 0.8612C) 0.7475D) 0.6338

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E) 0.1590



-1140. 0.08123

-242 0.1187

0 0.1915

-22.5 0.1137

Determine (in kJ/mol K).A) 7.63B) 6.36C) 84.1D) 5.20E) 7.78



-1140. 0.08116

-242 0.1187

0 0.1915

-22.5 0.1137

Determine (in kJ/mol). (Ignore significant figures for this problem.)

A) –190.8B) –2274.4C) –39.0D) –1896.6E) –1548.4

77. Calculate Ksp for the salt NaCl at 25oC.

Substance (in kJ/mol)Na+(aq) -262.0Cl-(aq) -131.0NaCl(s) -383.6

A) 44B) 4.4e19C) 9.4

D) 4.4E) 0.44

78. Determine for the weak acid, HF, at 25oC. (Ka = 7.23e–4)

A) 1.5 kJB) 177 kJC) 7.78 kJD) 1.79 kJE) 17.9 kJ

79. Consider the reaction

at 25oC for which the following data are relevant:

11.286 kJ/mol 655.3 J/K mol

33.150 kJ/mol 239.9 J/K mol

? 204.8 J/K mol

Calculate for the reaction.A) 110.028 kJB) 10.578 kJC) 121.314 kJD) 21.864 kJE) 155.172 kJ



11.29 kJ/mol 355.34 J/K mol

33.15 kJ/mol 239.90 J/K mol

? 204.80 J/K mol

Calculate for the reaction.A) 809.06 J/KB) 89.36 J/KC) 453.72 J/KD) –265.98 J/KE) 1164.40 J/K



11.29 kJ/mol 355.30 J/K mol

33.15 kJ/mol 239.90 J/K mol

? 204.80 J/K mol

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Calculate for the reaction at 25oC.A) –1.35e5 kJB) 98.7 kJC) –25.2 kJD) 135 kJE) 0

Use the following to answer question 82:Consider the reaction 2N2O5(g) 4NO2(g) + O2(g) at 25°C for which the following data are relevant:

H S° N2O5 11.29 kJ/mol 655.3 J/K mol NO2 33.15 kJ/mol 239.9 J/K mol O2 ? 204.8 J/K mol82. Which of the following is true for this reaction?

A) Both H° and S° favor the reaction's spontaneity.B) Both H° and S° oppose the reaction's spontaneity.C) H° favors the reaction, but S° opposes it.D) H° opposes the reaction, but S° favors it.E) The reaction cannot occur at room temperature.



11.29 kJ/mol 355.28 J/K mol

33.15 kJ/mol 239.90 J/K mol

? 204.80 J/K molThe reaction is allowed to proceed until all substances involved have reached their equilibrium concentrations.

Under those conditions, what is for the reaction?A) –1.35e5 kJB) 98.7 kJC) –25.2 kJD) 135 kJE) 0

84. At 699 K, = -23.25 kJ for the reaction

Calculate G for this reaction if the reagents are both supplied at 10.0 atm pressure and the product is at 2.15 atm pressure.

A) –17.9 kJB) 17.9 kJC) 5.4 kJD) –41.1 kJE) 41.1 kJ

85. Assume that the reaction

occurs in an ideal mixture of ideal gases. At 700. K, Kp =

2.78. At this temperature, equals:A) 0 kJB) 5.95 kJC) –2.98 kJD) –5.95 kJE) –2.58 kJ


for which = -200. kJ and = -187.3 J/K at 25oC.

Assuming that and are independent of temperature, calculate the temperature where Kp = 1. (Ignore significant figures for this problem.)

A) 968. KB) 2068 KC) 200. KD) 1068 KE) none of these

87. For the following reaction, CO2(g) + 2H2O(g) CH4(g) + 2O2(g), H° = 803 kJ which of the following will increase K?

A) decrease number of moles of methaneB) increase volume of systemC) increase the temperature of systemD) all of the aboveE) none of the above

88. For a particular reaction the equilibrium constant is

1.49e–2 at 370.oC and is +16.0 kJ at 25oC. Assuming

and are temperature independent, calculate for the reaction.

A) 8.27 J/KB) –8.27 J/KC) –10.1 J/KD) 10.1 J/KE) none of these

89. Calculate for

at 599.8 K, using the following data:

Kp = 2.3 106 at 599.8 K

Kp = 1.8 1037 at 599.8 KA) 141 kJB) –501 kJC) 501 kJD) –287 kJE) 287 kJ

90. For which of the following processes would S° be expected to be most positive?

A) O2(g) + 2H2(g) 2H2O(g)

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B) H2O(l) H2O(s)C) NH3(g) + HCl(g) NH4Cl(g)D) 2NH4NO3(s) 2N2(g) + O2(g) + 4H2O(g)E) N2O4(g) 2NO2(g)

91. Consider the following hypothetical reaction (at 318.1 K). Standard free energies in kJ/mol are given in parentheses.

A B + C = ? (-32.2) (207.8) (-237.0)What is the value of the equilibrium constant for the reaction at 318.1 K?

A) 0.32B) 1.0C) 6.2e4D) 273E) 0.41

92. The equilibrium constant Kp for the dissociation reaction of Cl2

2Cl(g)was measured as a function of temperature (in K). A graph of ln Kp versus 1/T for this reaction gives a straight line with a slope of -1.352 104 and an intercept of 14.19. The value of

for this dissociation reaction is:A) 1.707 J/K molB) 236.0 J/K molC) 118.0 J/K molD) 58.99 J/K molE) none of these

93. The following reaction has a value of 42.59 kJ/mol at 25oC.

Calculate the Ka for the acid HB.

A) 9.83e–1B) –17.2C) 3.42e–8D) 4.26e4E) –205

94. The standard free energy of formation of nitric oxide, NO, at 1000. K (roughly the temperature in an automobile engine during ignition) is 77.6 kJ/mol. Calculate the equilibrium constant for the reaction

2NO(g)at 1000. K.

A) 1.55e5B) 8.84e–5C) –14.7D) 7.81e–9E) 0.948

95. Consider the reaction 2NO2(g) N2O4(g); H° = –56.8 kJ S° = –175 J/K In a container (at 298 K) N2O4(g) and NO2(g) are mixed with initial partial pressures of 2.4 atm and 0.42 atm, respectively. Which of the following statements is correct?

A) Some N2O4(g) will decompose into NO2(g).B) Some NO2(g) will dimerize to form N2O4(g).C) The system is at equilibrium at these initial pressures.D) The final total pressure must be known to answer this question.E) None of these.

96. Consider the gas phase reaction

for which = -56.98 kJ and K = 1.5 106 at 25oC.

Calculate at 25oC for the following reaction:

A) 56.98 kJB) –114.0 kJC) –28.5 kJD) 3247 kJ


for which = -57.0 kJ and K = 1.47e6 at 25oC. Calculate K for the following reaction at 25oC:

A) 2.94e6B) 2.16e12C) 7.35e5D) 1.21e3E 1.47e6


for which = -57.0 kJ and K = 1.51e6 at 25oC. Calculate

at 25oC for the following reaction:

A) –70.5 kJB) –5.91 kJC) –35.2 kJD) 5.91 kJE) 70.5 kJ


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for which = -57.0 kJ and K = 1.48e6 at 25oC. Calculate

at 25oC for the following reaction:

A) 236 J/KB) –146 J/KC) –236 J/KD) –264 J/KE) 264 J/K

Use the following to answer questions 100-101: Consider the gas phase reaction NO + (1/2)O2 NO2 for which H° = –57.0 kJ and K = 1.5 × 106 at 25°C.100. For this system at equilibrium, how will raising the temperature affect the amount of NO present?

A) The amount of NO will increase.B) The amount of NO will decrease.C) The amount of NO will remain the same.D) Cannot be determined.E) Answer depends on the value of K.

101. What would be the effect on the amount of NO present of compressing the equilibrium system to a smaller volume, while keeping the temperature constant?

A) The amount of NO will increase.B) The amount of NO will decrease.C) The amount of NO will remain the same.D) Cannot be determined.E) Answer depends on the value of K.

102. Given

at 25oC, Ka = 1.75e–5. What is

at 25oC?A) –2.71e4 JB) 2.71e4 JC) 2.28e3 JD) –2.28e3 JE) 27.1 J

103. Given

at 25oC, Ka = 1.83e–5. What is

at 25oC for a solution in which the initial concentrations are:

= 0.10 M

= 2.0 10-8 M

= 0.010 MA) –76.7 kJB) 76.7 kJC) 22.6 kJD) –22.6 kJE) 27.0 kJ

104. The equilibrium constant of a certain reaction was measured at various temperatures to give the plot shown below. What is S° for the reaction in J/mol K?

A) 0.20B) 3.0C) 25D) –50.E) –8.3 × 103

105. Consider a weak acid, HX. If a 0.10 M solution of

HX has a pH of 4.26 at 25oC, what is for the acid's dissociation reaction at 25oC?

A) –42.9 kJB) 3.60 kJC) 0D) –3.60 kJE) 42.9 kJ

106. For the reaction

= -13.461 kJ. The Kp for this reaction at 700. K is:

A) 10.1B) 1.00C) 1.54D) 2.31E) none of these

107. For the reaction 2HF(g) H2(g) + F2(g), G° = 38.3 kJ, at 1000 K. If, at this temperature, 5.00 moles of HF(g), 0.500 moles of H2(g), and 0.75 moles of F2(g) are mixed in a 1.00-L container:

A) Some HF will decompose (to yield H2 and F2).B) The system is at equilibrium.C) Some HF will be formed (from H2 and F2).D) Not enough data are given to answer this question.E) None of these (a-d).

Use the following to answer questions 108-110:Consider the following system at equilibrium at 25°C:

PCl3(g) + Cl2(g) PCl5(g)

for whichH° = –92.5 kJ at 25°C.

108. If the temperature of the system is raised, the ratio of the partial pressure of PCl5 to the partial pressure of PCl3 will

A) increase.B) decrease.C) stay the same.D) impossible to tell without more information.E) none of these

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109. When some Cl2(g) is added at constant volume and temperature, the ratio of the partial pressure of PCl5 to the partial pressure of PCl3 will


110. When the volume is decreased at constant temperature, the ratio of the partial pressure of PCl5 to the partial pressure of PCl3 will


111. Water gas, a commercial fuel, is made by the reaction of hot coke carbon with steam.

When equilibrium is established at 833oC the concentrations of CO, H2, and H2O are 4.00 10-2, 4.00 10-2, and 1.00

10-2 mole/liter, respectively. Calculate the value of for this reaction at 833oC.

A) 12.7 kJB) –12.75 kJC) 55.09 kJD) 16.85 kJE) none of these

Use the following to answer question 112:The equilibrium constant Kp (in atm) for the dissociation reaction of Cl2 Cl2 2Cl was measured as a function of temperature (in K). A graph of ln Kp versus 1/T for this reaction gives a straight line with a slope of –1.352 × 104 and an intercept of 14.51.

112. From these data, which of the following statements is true?

A) The reaction is exothermic.B) The reaction is endothermic.C) The reaction rate is highD) The reaction is not spontaneous.E) None of these.

113. The equilibrium constant Kp (in atm) for the dissociation reaction of Cl2

was measured as a function of temperature (in K). A graph of ln Kp versus 1/T for this reaction gives a straight line with a slope of -1.529e4 and an intercept of 14.51. The value of

for this dissociation reaction is:A) –127.1 kJB) 127.1 kJC) 1.839 kJD) –1.839 kJ

E) none of these

114. In which of the following changes is the work done by the system the largest at 25°C?

A) an isothermal free expansion of an ideal gas from 1 to 10 litersB) an isothermal expansion of an ideal gas from 1 to 10 liters against an opposing pressure of 1 atmC) an isothermal expansion of an ideal gas from 1 to 10 liters against an opposing pressure of 5 atmD) an isothermal reversible expansion of an ideal gas from 1 to 10 litersE) the work is the same for processes a–d

115. For a certain process, at 300. K, = -36.4 kJ and

= -7.0 kJ. If the process is carried out reversibly, the amount of useful work that can be performed is

A) –43.4 kJB) -7.0 kJC) –29.4 kJD) –36.4 kJE) 29.4 kJ

116. For a certain process, at 300. K, = -44.4 kJ and

= -7.0 kJ. If the process is carried out so that no useful

work is performed, isA) 44.4 kJB) 7.0 kJC) 0D) -7.0 kJE) –44.4 kJ

Use the following to answer questions 117-120: Would you predict an increase or decrease in entropy for each of the following?

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117. The freezing of water

118. 2H2(g) + O2(g) 2H2O(g)

119. 2KClO3(s) 2KCl(s) + 3O2(g)

120. He(g) at 3 atm He(g) at 1 atm

121. In which process is S expected to be positive?A) A reaction which forms a solid precipitant from aqueous solutions.B) An ideal gas being compressed at a constant temperature and against a constant pressure.C) Water freezing below its normal freezing point.D) A spontaneous endothermic process at a constant temperature and pressure.E) None of these.

122. Of S, Ssurr, Suniv, and G, which are state functions?A) S, Ssurr, Suniv, and G are all state functions.B) Only S, Suniv, and G are state functionsC) Only S and G are state functionsD) Only S, Ssurr, and Suniv are state functions.E) Only Suniv and G are state functions.

Use the following to answer questions 123-124:Consider two perfectly insulated vessels. Vessel #1 initially contains an ice cube at 0°C and water at 0°C. Vessel #2 initially contains an ice cube at 0°C and a saltwater solution at 0°C. Vessel #1

S Ssurr Suniv

a) 0 0 +b) + - +c) + + +d) 0 0 0e) + - 0

123. Determine the sign of S, Ssurr, and Suniv for the system (ice/water) in Vessel #1.

S Ssurr Suniv

A) 0 0 0B) + - 0C) + + +D) + - +E) + 0 +

124. Determine the sign of S, Ssurr, and Suniv for the system (ice/saltwater) in Vessel #2.

S Ssurr Suniv

A) 0 0 0B) + - 0C) + + +D) + - +E) + 0 +

125. Which of the following is true?A) By spontaneous we mean that the reaction or process will always proceed to the right (as written) even if very slowly. Increasing the temperature may speed up the reaction, but it does not affect the spontaneity of the reaction.B) By spontaneous we mean that the reaction or process will always proceed to the left (as written) even if very slowly. Increasing the temperature may speed up the reaction, but it does not affect the spontaneity of the reaction.C) By spontaneous we mean that the reaction or process will always proceed to the left (as written) even if very slowly. Increasing the temperature may speed up the reaction and it generally affects the spontaneity of the reaction.D) By spontaneous we mean that the reaction or process will always proceed to the right (as written) even if very slowly. Increasing the temperature may speed up the reaction, and it generally affects the spontaneity of the reaction.E) None of the above is true.

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Answer Key

1. C2. E3. A4. B5. C6. E7. D8. B9. C10. C11. A12. B13. B14. D15. A16. B17. D18. E19. A20. D21. E22. D23. C24. A25. E26. C27. D28. E29. B30. D31. E32. B33. D

34. B35. A36. A37. B38. B39. B40. A41. A42. E43. A44. B45. E46. False47. False48. True49. False50. C51. A52. D53. B54. A55. B56. E57. E58. A59. E60. C61. D62. C63. A64. B65. D66. E

67. A68. D69. C70. C71. A72. E73. C74. D75. A76. B77. A78. E79. A80. C81. C82. D83. E84. D85. D86. D87. C88. C89. A90. D91. A92. C93. C94. D95. A96. B97. B98. A99. B

100. A101. B102. B103. D104. C105. E106. A107. C108. B109. A110. A111. D112. B113. B114. D115. D116. E117. decrease in entropy118. decrease in entropy119. increase in entropy120. increase in entropy121. D122. C123. D124. E125. D

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Unit 19 Study Guide