University of South Florida

CHM 2046

1)For which process is DS negative?

1. A. evaporation of 1 mol of CCl4(l)
   1. mixing 5 mL ethanol with 25 mL water
   2. compressing 1 mol Ne at constant temperature from 1.5 L to 0.5 L
   3. raising the temperature of 100 g Cu from 275 K to 295 K
   4. grinding a large crystal of KCl to powder

 

 

               

 

2. 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)
   1. T10H0
   2. T8H2
   3. T7H3
   4. T5H5
   5. T4H6

 

 

               

 

3. If two pyramid-shaped dice (with numbers 1 through 4 on the sides) were tossed, which outcome has the highest entropy?
   1. The sum of the dice is 3.
   2. The sum of the dice is 4.
   3. The sum of the dice is 5.
   4. The sum of the dice is 6.
   5. The sum of the dice is 7.

 

 

               

 

4. A two-bulbed flask contains 5 particles. What is the probability of finding all 5 particles on the left side? A) 2.50%

B)     2.24%

C)     3.13%

D)   0.20%

E)     6.25%

 

 

               

5. Which of the following shows a decrease in entropy?
   1. precipitation
   2. gaseous reactants forming a liquid
   3. a burning piece of wood
   4. melting ice
   5. two of these

 

 

               

 

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

 

 

I.

 

 

 

2. Br2(g) ® Br2(l)
3. NaBr(s) ® Na⁺(aq) + Br^–(aq)

IV.        O2(298 K) ® O2(373 K)

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

 

1. I
2. II, V
3. I, III, IV
4. I, II, III, IV
5. I, II, III, V

 

 

               

 

7. Consider the following processes:

I.         condensation of a liquid

II         increasing the volume of 1.0 mol of an ideal gas at constant temperature

3. dissolving sugar in water
4. heating 1.0 mol of an ideal gas at constant volume For how many of these is DS positive?

1. 0
2. 1
3. 2
4. 3
5. 4

 

 

               

 

8. The second law of thermodynamics states that:
   1. The entropy of a perfect crystal is zero at 0 K.
   2. The entropy of the universe is constant.
   3. The energy of the universe is increasing.
   4. The entropy of the universe is increasing.
   5. The energy of the universe is constant.

 

 

               

 

9. Which of the following statements is true?
   1. The total energy and entropy of the universe are both increasing.
   2. The total energy of the universe is increasing, but the entropy is constant.
   3. The total energy of the universe increases, while the entropy decreases.

1. 4. The total energy of the universe is constant, but the entropy is increasing.
   5. None of these.

 

 

               

 

10. 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
    1. DH < 0
    2. DSuniv > 0
    3. DSsys< 0
    4. DSsurr > 0
    5. none of these

 

 

               

 

11. A chemical reaction is most likely to be spontaneous if it is accompanied by
    1. increasing energy and increasing entropy
    2. lowering energy and increasing entropy
    3. increasing energy and decreasing entropy
    4. lowering energy and decreasing entropy
    5. none of these (A-D)

 

 

               

 

12. 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 0°C is melted by heat supplied from surroundings at 276 K, what is the entropy change in the surroundings, in J/K?

A)   22.1

B)     21.8

C)     0.0

D)   –21.8

E)     –22.1

 

 

               

 

13. 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?
    1. 326 kJ
    2. 1.32 kJ
    3. –141 kJ
    4. 105 kJ
    5. 141 kJ

 

 

               

 

14. The heat of vaporization for 1.0 mole of water at 100.°C and 1.0 atm is 40.56 kJ/mol. Calculate DS for the process H2O(l) ® H2O(g) at 100.°C.
    1. 109 J/K mol
    2. –109 J/K mol
    3. 406 J/K mol
    4. –406 J/K mol
    5. none of these

               

 

15. A change of state that occurs in a system is accompanied by 52.3 kJ of heat, which is transferred to the surroundings at a constant pressure and a constant temperature of 300. K. For this process DSsurr is:
    1. 52.3 kJ/K

B)     –52.3 kJ/K

C)     –174 J/K

4. 174 J/K
5. 248 kJ/K

 

 

               

 

16. The enthalpy of vaporization of ammonia is 23.35 kJ/mol at its boiling point (–33.4°C). Calculate the value of DSsurr when 1.00 mole of ammonia is vaporized at –33.4°C and 1.00 atm.
    1. 0

B)     –6.99 ´ 10² J/K mol

C)     9.74 ´ 10¹ J/K mol

D) –9.74 ´ 10¹ J/K mol

E)     6.99 ´ 10² J/K mol

 

 

               

 

17. DSsurr is             for exothermic reactions and        for endothermic reactions.
    1. favorable, unfavorable
    2. unfavorable, favorable
    3. favorable, favorable
    4. unfavorable, unfavorable
    5. cannot tell

 

 

               

 

18. Which of the following is true for exothermic processes?
    1. DSsurr < 0
    2. DSsurr = –DH/T
    3. DSsurr = 0
    4. DSsurr > 0
    5. two of these

 

 

               

 

At 1 atm, liquid water is heated above 100°C.

 

19. DSsurr for this process is
    1. greater than zero
    2. less than zero
    3. equal to zero
    4. more information needed to answer this question
    5. none of these (A-D)

 

 

               

20. DSsys for this process is
    1. greater than zero
    2. less than zero
    3. equal to zero
    4. more information needed to answer this question
    5. none of these (A-D)

 

 

               

 

21. DSuniv for this process is
    1. greater than zero
    2. less than zero
    3. equal to zero
    4. more information needed to answer this question
    5. none of these (A-D)

 

 

               

 

22. Given that DHvap is 58.2 kJ/mol, and the boiling point is 83.4°C, 1 atm, if one mole of this substance is vaporized at 1 atm, calculate DSsurr.
    1. –163 J/K mol
    2. 163 J/K mol
    3. 698 J/K mol
    4. –698 J/K mol
    5. 0

 

 

               

 

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

 

ANS:      F                            

 

24. For any given process, DSsurr and DSsys have opposite signs.

 

ANS:      F                            

 

25. If DSsurr = –DSsys, the process is at equilibrium.

 

ANS:      T                            

 

26. Which of the following is true?
    1. 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.
    2. 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.
    3. 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.
    4. 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.

1. 5. None of the above is true.

 

 

               

                                                                                              

 

27. Substance X has a heat of vaporization of 55.9 kJ/mol at its normal boiling point (423°C). For the process X(l) ® X(g) at 1 atm and 423°C calculate the value of DSuniv.
    1. 0
    2. 80.3 J/K mol
    3. 132 J/K mol
    4. –80.3 J/K mol
    5. –132 J/K mol

 

 

               

 

28. Substance X has a heat of vaporization of 58.4 kJ/mol at its normal boiling point (423°C). For the process X(l) ® X(g) at 1 atm and 423°C calculate the value of DSsurr.
    1. 0
    2. 83.9 J/K mol
    3. 138 J/K mol
    4. –83.9 J/K mol
    5. –138 J/K mol

 

 

               

 

29. Substance X has a heat of vaporization of 47.1 kJ/mol at its normal boiling point (423°C). For the process X(l) ® X(g) at 1 atm and 423°C calculate the value of DS.
    1. 0
    2. 67.7 J/K mol
    3. 111 J/K mol
    4. –67.7 J/K mol
    5. –111 J/K mol

 

 

               

 

30. Substance X has a heat of vaporization of 64.4 kJ/mol at its normal boiling point (423°C). For the process X(l) ® X(g) at 1 atm and 423°C calculate the value of DG.
    1. 0 J

B)     92.5 J

3. 152 J

D) –92.5 J

E)     –152 J

 

 

               

 

31. The enthalpy of vaporization of ammonia is 23.35 kJ/mol at its boiling point (–33.4°C). Calculate the value of DS when 1.00 mole of ammonia is vaporized at –33.4°C and 1.00 atm.
    1. 0

B)     –6.99 ´ 10² J/K mol

C)     9.74 ´ 10¹ J/K mol

D) –9.74 ´ 10¹ J/K mol

E)     6.99 ´ 10² J/K mol

               

 

32. DS is                  for exothermic reactions and        for endothermic reactions.
    1. favorable, unfavorable
    2. unfavorable, favorable
    3. favorable, favorable
    4. unfavorable, unfavorable
    5. cannot tell

 

 

               

 

 

33. For the process CHCl3(s) ® CHCl3(l), DH° = 9.19 kJ/mol and DS° = 43.9 J/mol/K. What is the melting point of chloroform?

A)   –64 °C

B)     209 °C

C)     130 °C

4. 64 °C

E)     –130 °C

 

 

               

 

 

34. Given that DHvap is 60.3 kJ/mol, and the boiling point is 83.4°C, 1 atm, if one mole of this substance is vaporized at 1 atm, calculate DS.
    1. –169 J/K mol
    2. 169 J/K mol
    3. 723 J/K mol
    4. –723 J/K mol
    5. 0

 

 

               

 

 

35. DH° is zero for a chemical reaction at constant temperature.

 

ANS:      F                            

 

 

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. In each vessel, consider the "system" to be the ice, and the "surroundings" to be the liquid.

 

36. Determine the sign of DSsys, DSsurr, and DSuniv for the contents of Vessel #1.

DSsys   A) 0		DSsurr   0	0	DSuniv
B)     + C)     + D)   + E)     +		– + – 0	0 + + +
ANS:	B

 

37. Determine the sign of DSsys, DSsurr, and DSuniv for the system (ice/saltwater) in Vessel #2.

DSsys   A) 0		DSsurr   0	0	DSuniv
B)     + C)     + D)   + E)     +		– + – 0	0 + + +
ANS:	D

 

 

38. The melting point of water is 0°C at 1 atm pressure because under these conditions:
    1. DS for the process H2O(s) ® H2O(l) is positive.
    2. DS and DSsurr for the process H2O(s) ® H2O(l) are both positive.
    3. DS and DSsurr for the process H2O(s) ® H2O(l) are equal in magnitude and opposite in sign.
    4. DG is positive for the process H2O(s) ® H2O(l).
    5. None of these is correct.

 

 

               

 | second law of thermodynamics | entropy change for a phase transition              

 

39. For the vaporization of a liquid at a given pressure:
    1. DG is positive at all temperatures.
    2. DG is negative at all temperatures.
    3. DG is positive at low temperatures, but negative at high temperatures (and zero at some temperature).
    4. DG is negative at low temperatures, but positive at high temperatures (and zero at some temperature).
    5. None of these (A-D).

 

 

               

 | second law of thermodynamics | entropy change for a phase transition              

 

40. Which of the following statements is always true for a spontaneous process?

1. DSsys > 0
2. DSsurr > 0
3. DSuniv > 0
4. DGsys > 0

 

1. I
2. III
3. IV
4. I and III
5. III and IV

 

 

               

 

 

41. For a spontaneous exothermic process, which of the following must be true?
    1. DG must be positive.
    2. DS must be positive.
    3. DS must be negative.
    4. Two of the above must be true.
    5. None of the above (A-C) must be true.

               

 

 

42. 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)               DG = –45.54 kJ

DH = –44.12 kJ DS = –4.76 J/K

Which of the following is consistent with this information?

1. 1. The reactants are thermodynamically more stable than the products.
   2. The reaction has a small equilibrium constant.
   3. The ultraviolet light raises the temperature of the system and makes the reaction more favorable.
   4. The negative value for DS slows down the reaction.
   5. The reaction is spontaneous, but the reactants are kinetically stable.

 

 

               

 

 

43. For a particular chemical reaction DH = 4.3 kJ and DS = –19 J/K. Under what temperature condition is the reaction spontaneous?
    1. When T < –226 K.
    2. When T < 226 K.
    3. The reaction is spontaneous at all temperatures.
    4. The reaction is not spontaneous at any temperature.
    5. When T > 226 K.

 

 

               

 

 

44. For a certain process at 355 K, DG = –11.8 kJ and DH = –9.2 kJ. Therefore, DS for the process is
    1. 0 J/K mol
    2. 7.3 J/K mol
    3. –7.3 J/K mol
    4. –25.9 J/K mol
    5. 25.9 J/K mol

 

 

               

 

 

45. Consider the freezing of liquid water at –10°C. For this process what are the signs for DH, DS, and DG?

 

DH		DS		DG
A)   + B)     + – – –	– – + + –		0 – 0 – –

 

 

46. For the process of a certain liquid vaporizing at 1 atm, DH°vap = 54.2 kJ/mol and DS°vap= 74.1 J/mol K. Assuming these values are independent of T, what is the normal boiling point of this liquid?

A) 731 °C

B)     1004 °C

C)     458 °C

D) 0.731 °C

E)     none of these

               

 

 

47. For the reaction A + B ® C + D, DH° = +40 kJ and DS° = +50 J/K. Therefore, the reaction under standard conditions is
    1. spontaneous at temperatures less than 10 K
    2. spontaneous at temperatures greater than 800 K
    3. spontaneous only at temperatures between 10 K and 800 K
    4. spontaneous at all temperatures
    5. nonspontaneous at all temperatures

 

 

               

 

 

48. In which case must a reaction be spontaneous at all temperatures?
    1. DH is positive, DS is positive.
    2. DH = 0, DS is negative.
    3. DS = 0, DH is positive.
    4. DH is negative, DS is positive.
    5. None of these.

 

 

               

 

 

49. For the process S8 (rhombic) ® S8 (monoclinic) at 110°C, DH = 3.21 kJ/mol and DS = 8.70 J/K × mol (at 110°C). Which of the following is correct?
    1. This reaction is spontaneous at 110°C (S8 (monoclinic) is stable).
    2. This reaction is spontaneous at 110°C (S8 (rhombic) is stable).
    3. This reaction is nonspontaneous at 110°C (S8 (rhombic) is stable).
    4. This reaction is nonspontaneous at 110°C (S8 (monoclinic) is stable).
    5. Need more data.

 

 

               

 

 

50. 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 DH for the I ®II phase transition is –

743.07 J/mol, and DS for the same transition is -17.0 J/K mol. At what temperature are Solids I and II in equilibrium?

A)   13.6 K

B)     43.7 K

C)     19.8 K

D)   98.2 K

E)     They can never be in equilibrium because they are both solids.

 

 

               

 

 

51. At constant pressure, the following reaction 2NO2(g) ® N2O4(g) is exothermic. The reaction (as written) is
    1. always spontaneous
    2. spontaneous at low temperatures, but not high temperatures
    3. spontaneous at high temperatures, but not low temperatures
    4. never spontaneous
    5. cannot tell

 

 

               

 

 

52. Given that DHvap is 53.3 kJ/mol, and the boiling point is 83.4°C, 1 atm, if one mole of this substance is vaporized at 1 atm, calculate DG.

A) –150 J

2. 150 J
3. 639 J

D) –639 J

E)     0 J

 

 

               

 

 

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)    DH = –789 kJ/mol

Substance	S° (J/mol K)
Fe(OH)3(s)	107
Fe(s)	27
O2(g)	205
H2O(l)	70

 

 

53. Determine DSsurr for the reaction (in kJ/mol K) A) 3.14

B)     0.937

C)     0.378

D)   1.31

E)     2.65

 

 

               

 

 

54. Determine DSuniv for the reaction (in kJ/mol K) A) 0.23

B)     2.3

C)     0.36

D)   2.8

E)     3.6

 

 

               

 

 

55. What must be true about DG for this reaction?
    1. DG = DH
    2. DG = 0
    3. DG > 0
    4. DG < 0
    5. DG = DSuniv

 

 

               

 

 

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

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

A) 0.39 °C

B)     388 °C

C)     661 °C

D)   279 °C

E)     115 °C

 

 

               

 

 

57. The following reaction takes place at 120°C: H2O(l) ® H2O(g)         DH = 44.0 kJ/mol DS = 0.119 kJ/mol K Which of the following must be true?
    1. The reaction is not spontaneous.
    2. The reaction is spontaneous.
    3. DG = 0
    4. DG < 0
    5. Two of these.

 

 

               

 

 

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 25°C.

Substance	DHf° (kJ/mol)	S° (kJ/mol K)
Cr2O3(g)	–1147	0.08118
H2O(l)	–242	0.1187
N2(g)	0	0.1915
(NH4)2Cr2O7(s)	–22.5	0.1137

 

 

58. Determine DSuniv° (in kJ/mol K). A) 7.66

B)     6.39

C)     84.3

D)   5.22

E)     6.03

 

 

               

 

 

59. Determine DS° reaction (in kJ/mol K). A) 0.2777

B)     0.8612

C)     0.7475

D)   0.6338

E)     0.1590

 

 

               

 

 

60. Determine DG° (in kJ/mol). A) –191.4

B)     –2281.4

C)     –38.9

D)   1903.6

E)     –1555.4

 

 

               

                                              

 

61. The third law of thermodynamics states:
    1. The entropy of the universe is increasing.
    2. The entropy of the universe is constant.
    3. The entropy is zero at 0 K for a perfect crystal.
    4. The absolute entropy of a substance decreases with increasing temperature.
    5. The entropy of the universe equals the sum of the entropy of system and surroundings.

 

 

               

 

62. For which of the following processes would DS° be expected to be most positive? A) O2(g) + 2H2(g) ® 2H2O(g)

2. H2O(l) ® H2O(s)
3. NH3(g) + HCl(g) ® NH4Cl(g)

D) 2NH4NO3(s) ® 2N2(g) + O2(g) + 4H2O(g)

E)     N2O4(g) ® 2NO2(g)

 

 

               

 

 

63. Which of the following statements is (are) always true?

1. In order for a process to be spontaneous, the entropy of the universe must increase.

2. 

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

 

DSuniv =

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

 

1. I
2. I, IV
3. I, III, IV
4. II, IV
5. II

 

 

               

 

 

64. In which process is DS expected to be positive?
    1. a reaction that forms a solid precipitant from aqueous solutions
    2. an ideal gas being compressed at a constant temperature and against a constant pressure
    3. water freezing below its normal freezing point
    4. a spontaneous endothermic process at a constant temperature and pressure
    5. none of these

 

 

               

 

 

65. In which reaction is DS° expected to be positive?

A) I2(g) ® I2(s)

 

B)     H2O(l) ® H2O(s) C)

 

CH3OH(g) +     O2(g) ® CO2(g) + 2H2O(l)

D) 2O2(g) + 2SO(g) ® 2SO3(g)

E)     none of these

 

 

               

                                                             

 

66. 

    For the dissociation reaction of the acid HF: HF(aq)            H⁺(aq) + F^–(aq)

DS is observed to be negative. The best explanation is:

1. 1. This is the expected result since each HF molecule produces two ions when it dissociates.
   2. Hydration of the ions produces the negative value of DS.
   3. The reaction is expected to be exothermic and thus DS should be negative.
   4. The reaction is expected to be endothermic and thus DS should be negative.
   5. None of these can explain the negative value of DS.

 

 

               

 

 

67. Consider the dissociation of hydrogen:

 

H2(g)           2H(g)

 

One would expect that this reaction:

1. 1. will be spontaneous at any temperature
   2. will be spontaneous at high temperatures
   3. will be spontaneous at low temperatures
   4. will not be spontaneous at any temperature
   5. will never happen

 

 

               

 

 

68. When a stable diatomic molecule spontaneously forms from its atoms, what are the signs of DH°, DS°, and DG°?

 

DH        DS     DG

 

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

 

 

               

 

 

Consider the reaction

 

2N2O5(g)           4NO2(g) + O2(g)

 

at 25°C for which the following data are relevant:

	DHf°	S°
N2O5	11.289 kJ/mol	355.32 J/K mol
NO2	33.150 kJ/mol	239.90 J/K mol
O2	0 kJ/mol	204.80 J/K mol

 

 

69. Calculate DS° for the reaction. A) 809.08 J/K

B)     89.38 J/K

C)     453.76 J/K

D)   –265.94 J/K

E)     1164.40 J/K

 

 

               

 

 

70. Calculate DH° for the reaction.