Deck 19: Spontaneous Change: Entropy and Free Energy

Question 1

A spontaneous reaction is one that must have a negative value of ΔH.

Answer 1

False

Question 2

If a process is spontaneous, the reverse process is nonspontaneous.

Answer 2

True

Question 3

ΔG∘ is independent of temperature.

Answer 3

False

Question 4

Choose the correct statements concerning entropy. I) As two gasses mix, ΔS is positive.
II) Entropy is a thermodynamic property related to the degree of disorder.
III) As temperature in a gas decreases, ΔS is positive.
IV) Molecules in the liquid state have higher entropy than molecules in the gaseous state.

A) I and III
B) I, II, III
C) I and II
D) I, II, IV
E) II and III

Question 5

A nonspontaneous reaction can be made to occur by coupling it with a spontaneous reaction to form an overall spontaneous reaction.

Question 6

Which of the following processes would result in a decrease in system entropy?

A) melting of an ice cube
B) sublimation of a moth ball
C) evaporation of a puddle of gasoline
D) a glass of cool lemonade warming in the sun
E) condensation of water vapor on a cold windshield

Question 7

ΔG is positive for a spontaneous reaction.

Question 8

Entropy is related to the way in which the energy of a system is distributed among the available microscopic energy levels.

Question 9

A spontaneous process will occur only if a some external action is continually applied.

Question 10

Indicate the statement(s) which are true for the process: Al+3(aq) + 3 OH-(aq) → Al(OH)₃(s)
If it occurs in a closed container.
I. ΔS increases because the final molecule is more complicated.
II. Entropy decreases because the product is in the solid phase.
III. The two ions achieve a high degree of order as they crystalize, therefore ΔS is positive.
IV. Entropy of the system is unchanged because the system is sealed and at a constant temperature.

A) I and II
B) I and III
C) II only
D) I, II, IV
E) I and IV

Question 11

Nonspontaneous reactions and spontaneous reactions cannot be coupled.

Question 12

The entropy of a pure perfect crystal at 25 K is zero.

Question 13

The entropy of a system always increases for a spontaneous process.

Question 14

Which material has the largest entropy?

A) cannot be determined
B) pure water
C) powdered sugar
D) salt water
E) crystalline salt

Question 15

A spontaneous process:

A) will happen quickly.
B) releases large amounts of energy.
C) requires an external action in order to begin reacting.
D) will continue on its own once begun.
E) is never endothermic.

Question 16

Which of the following has the highest entropy?

A) 1 mole of liquid water at 30°C
B) 1 mole of water vapor at 30°C
C) 1 mole of regular ice at -10°C
D) 1 mole of "dry ice" at -10°C
E) 1 mole of water under 10 atm of pressure at -10°C

Question 17

Standard Gibbs energy of formation requires the reactants be compounds in their standard state.

Question 18

Which of the following statements are true?
I. Liquids have more entropy than their solids.
II. Solutions have more entropy than the solids dissolved.
III. Gases and their liquids have equal entropy.
IV. Gases have less entropy than their solids.
V. Entropy of a substance increases as its temperature increases.

A) II), III), and V)
B) I), III), and V)
C) I), IV), and V)
D) I), II), and V)
E) II), IV) and V)

Question 19

Find correct statements.
I. A spontaneous process is a process that occurs in a system left to itself.
II. A nonspontaneous process will not occur unless some external force is applied.
III. If a reaction is spontaneous, the reverse is also spontaneous.
IV. Only spontaneous processes occur naturally.
V. Entropy is inversely proportional to the degree of randomness.

A) I), II) and V)
B) II), III), and IV)
C) I), II), and IV)
D) I), III) and IV)
E) I), IV), and V)

Question 20

A zero ΔG means the system is at equilibrium.

Question 21

If ΔG < 0 for a reaction, then the reaction is said to be:

A) endothermic
B) reversible
C) spontaneous
D) exothermic
E) fast

Question 22

Which of the following combinations of signs for ΔH and ΔS will always result in a reaction being nonspontaneous?

A) ΔH+, ΔS-
B) ΔH-, ΔS+
C) ΔH-, ΔS-
D) ΔH+, ΔS+
E) cannot determine without temperature

Question 23

Which of the following has the largest molar entropy?

A) I2(g)
B) Xe(g)
C) H2(g)
D) He(g)

Question 24

Choose the INCORRECT statement.

A) The third law of thermodynamics states that the entropy of a pure crystal at 298 K is zero.
B) ΔS° = Σ (ν S°) products - Σ (ν S°) reactants.
C) The activity of pure liquids or pure solids is 1.
D) ΔG° = -RT ln Keq.
E) ΔG° = ΔH° - TΔS°.

Question 25

For an exothermic reaction to be nonspontaneous at high temperatures, the enthalpy must be ________ while the entropy is ________.

A) positive, also positive
B) positive, negative
C) a relatively small negative value, also negative
D) a relatively large negative value, positive
E) a very large negative value, also negative

Question 26

If ΔG is positive for a certain reaction, then:

A) the reaction is spontaneous.
B) the reverse of the reaction is spontaneous.
C) the system is in equilibrium.
D) one would need to know the Kelvin temperature to determine spontaneity.
E) there would be no reaction possible for a negative value.

Question 27

The normal melting and boiling points of SO2 are 198 and 263 K, respectively. For a plot of the standard molar entropy of SO2 versus temperature, which of the following is INCORRECT?

A) At 263 K, S° is constant.
B) S° increases with increasing temperature.
C) S° equals zero at 0 K.
D) At 198 K, S° increases by the value of △Sfusion.

Question 28

The maximum quantity of energy available for useful work is:

A) constant
B) Gibbs energy
C) the entropy
D) the internal energy
E) the enthalpy

Question 29

The change in Gibbs energy for a reaction:

A) = ΔH - TΔS
B) = Q (heat)
C) = ΔS + TΔH
D) = ΔS - TΔH
E) = ΔH + TΔS

Question 30

The Gibbs energy change for a reaction is -298 kJ. The reaction is therefore:

A) exothermic
B) irreversible
C) spontaneous
D) endothermic
E) nonspontaneous

Question 31

Which of the following best expresses the increased degree of randomness associated with melting and sublimation, respectively?

A) ΔSfus - ΔSsub = 0
B) ΔSfus = 144.3 J/mol-K, ΔSsub = 9.0 J/mol-K
C) ΔSfus = 9.0 J/mol-K, ΔSsub = -144.3 J/mol-K
D) ΔH for both processes is zero
E) ΔSfus = 9.0 J/mol-K, ΔSsub = 144.3 J/mol-K

Question 32

Which of the following relations is true for the molar entropy of sublimation of a substance?

A) ΔSsub = ΔSfusion + ΔSvaporization
B) ΔSsub < ΔSvaporization
C) ΔSsub = ΔSfusion - ΔSvaporization
D) ΔSsub < (ΔSfusion + ΔSvaporization)

Question 33

Which of the following substances under equal conditions and in the same phase has the greatest molar entropy?

A) NO
B) NO2
C) N2O3
D) N2O4
E) N2O5

Question 34

In a sealed container, the rate of dissolving is equal to the rate of crystallization. Therefore we would expect:

A) ΔG < 0
B) ΔG > 0
C) ΔG = 0
D) ΔS = 0
E) must know ΔH to determine

Question 35

A reaction is spontaneous if:
I. ΔG is a negative value
II. both enthalpy and entropy increase
III. ΔH is negative and ΔS is positive
IV. both enthalpy and entropy decrease
V. ΔH is positive and ΔS is negative

A) I and III
B) I and II
C) II and V
D) III and IV
E) II and IV

Question 36

The following reaction is exothermic. 2N2O(g) → 2N2(g) + O2(g)
This means the reaction:

A) will be spontaneous at all temperatures
B) will be spontaneous only at high temperature
C) will be spontaneous only at low temperatures
D) is not spontaneous at any temperature

Question 37

The following reaction is endothermic. 2NH3(g) → N2(g) + 3H2(g)
This means the reaction:

A) will be spontaneous at high temperature
B) will be spontaneous at low temperature
C) is not spontaneous at any temperature
D) is spontaneous at all temperatures

Question 38

The change in Gibbs energy of a reaction:

A) = work
B) predicts speed
C) = ΔH + TΔS
D) depends on the standard state chosen
E) tells us if the reaction is spontaneous or not

Question 39

Choose the INCORRECT statement.

A) One form of the second law of thermodynamics is all spontaneous processes produce an increase in the entropy of the universe.
B) Gibbs energy is defined by: G = H - TS.
C) If ΔG < 0, the process is spontaneous.
D) If ΔG > 0, the process is nonspontaneous.
E) If ΔG = 0, the process is spontaneous.

Question 40

The fact that the entropies of vaporization for liquids which exhibit hydrogen bonding are greater than the 87 J/(mol ∙ K) which is expected of non-polar liquids is an exception to:

A) the Gibb's Energy Rule
B) the Third Law of Thermodynamics
C) the Clausius-Clapyeron Rule
D) the Second Law of Thermodynamics
E) Trouton's Rule

Question 41

The equilibrium constant for the reaction below is 7.2 x 10-4 at 298 K and 1 atm. HNO2(aq) + H2O(l) ⇌ NO2-(aq) + H3O+(aq)
When [HNO2(aq)] = 1.0 M and [NO2-(aq)] = [H3O+(aq)] = 1.0 x 10-5 M, calculate ΔG.

A) -39.1 kJ/mol
B) +17.9 kJ/mol
C) -17.9 kJ/mol
D) +39.1 kJ/mol

Question 42

For the reaction: CO(g) + 2 H2(g) → CH3OH(g) Kp = 91.4 at 350 K and Kp = 2.05 × 10-4 at 298 K.
What is the value of ΔH°?

A) 49.9 kJ/mol
B) 2.08 × 103 kJ/mol
C) 3.74 × 10-2 kJ/mol
D) 217 kJ/mol
E) 446 kJ/mol

Question 43

For the reaction, CaCO3(s) → CaO(s) + CO2(g) S° (J/mol K) 88.70 39.75 213.6
What is ΔS°rxn?

A) 262.5 J/mol ∙ K
B) -85.1 J/mol ∙ K
C) -164.7 J/mol ∙ K
D) 164.7 J/mol ∙ K
E) 85.1 J/mol ∙ K

Question 44

Consider the reaction: N2(g) + 3 X2(g) → 2 NX3(g)
△H° 0.0 0.0 -43 kJ/mol
S° 192 210 172 J/(mol∙K)
What is Keq for this reaction at 591 K?

A) 2.3 × 1017
B) 4.3 × 10-18
C) 1.04
D) 0.96
E) 132

Question 45

Predict whether ΔS is positive or negative for the following process: H2O(g) → H2O(s)

A) negative
B) positive
C) There is not enough information to determine.
D) ΔS doesn't change.
E) ΔS changes the same on both sides of the equation.

Question 46

Choose the INCORRECT statement.

A) The van't Hoff equation is ln =
.
B) Keq is independent of temperature.
C) In a thermodynamic equilibrium constant expression, the activity of a gas is replaced by its partial pressure in atmosphere.
D) In a Keq expression, the activity of a solution is replaced by its molarity.
E) If ΔG = 0, the process is at equilibrium.

Question 47

Order the following by increasing entropy. CO(g), COCl2(g), CO2(g), CaO(s)

A) CO2 < CO < CaO < COCl2
B) CaO < CO < CO2 < COCl2
C) COCl2 < CO < CaO < CO2
D) CO2 < CaO < COCl2 < CO
E) CO < CaO < COCl2 < CO2

Question 48

Which of the following quantities is generally independent of temperature? I) ΔH
II) ΔS
III) ΔG

A) I only
B) II only
C) III only
D) I and II
E) I, II, and III

Question 49

Predict whether ΔS is positive or negative for the following process: 2 Cl2O7(g) → 2 Cl2(g) + 7 O2(g)

A) negative
B) positive
C) There is not enough information to determine.
D) ΔS doesn't change.
E) ΔS changes the same on both sides of the equation.

Question 50

For the reaction PCl5(g) → PCl3(g) + Cl2(g) at 298 K, Keq = 1.87 × 10-7, ΔS° = 1.8192 J/(mol ∙K), what is ΔG° and is the reaction spontaneous?

A) 3.84 × 104 kJ/mol, no
B) 7.68 kJ/mol, no
C) -7.68 kJ/mol, yes
D) 38.4 kJ/mol, no
E) -38.4 kJ/mol, yes

Question 51

If the vapor pressure of water in an open system at 25°C is 23.8 mmHg, what is ΔG for the reaction below at 25°C? H2O(l) → H2O(g, 23.8 mmHg)

A) 0 kJ/mol
B) -8.58 kJ/mol
C) +8.58 kJ/mol
D) -0.720 kJ/mol

Question 52

For Cl2O(g) + 3/2 O2(g) → 2 ClO2 △H° = 126 kJ/mol, and ΔS° = -74.9 J/(mol∙deg) at 377°C. What is Keq?

A) 0.97
B) 6.12 × 10-7
C) 4.27 × 10-22
D) 9.17 × 10-15
E) 1.07 × 1014

Question 53

Choose the INCORRECT statement about coupled reactions.

A) The usual practice of coupling reactions is to join two nonspontaneous reactions.
B) The usual reason to couple reactions is to produce an overall spontaneous reaction.
C) The reaction added to a nonspontaneous reaction needs to be spontaneous.
D) The reaction added to a nonspontaneous reaction needs to be more spontaneous than the original reaction is nonspontaneous.
E) One of the coupled reactions has a negative ΔG, the other a positive ΔG.

Question 54

For the reaction, CO(g) + 2H2(g) → CH3OH(g) S° (J/mol K) 197.6 130.6 239.7
What is ΔS°rxn?

A) -88.5 J/mol ∙ K
B) -176.7 J/mol ∙ K
C) 219 J/mol ∙ K
D) 176.7 J/mol ∙ K
E) -219.1 J/mol ∙ K

Question 55

Predict whether ΔS is positive or negative for the following process: H2(g) + 1/2 O2(g) → H2O(g)

A) negative
B) positive
C) There is not enough information to determine.
D) ΔS doesn't change.
E) ΔS changes the same on both sides of the equation.

Question 56

Consider the reaction of 25.0 mL of 0.20 M AgNO3(aq) with 25.0 mL of 0.20 M NaBr(aq) to form AgBr(s) at 25°C. What is ΔG for this reaction? The Ksp of AgBr is 5.0 x 10-13 at 25°C.

A) -58.8 kJ/mol
B) -70.2 kJ/mol
C) +58.8 kJ/mol
D) +70.2 kJ/mol

Question 57

For the reaction, N2O4(g) → 2 NO2(g) S° (J/mol K) 304.2 240.0
What is ΔS°rxn?

A) 544.2 J/mol ∙ K
B) -64.2 J/mol ∙ K
C) 175.8 J/mol ∙ K
D) -175.8 J/mol ∙ K
E) 64.2 J/mol ∙ K

Question 58

Which of the listed reactions would couple with the following reaction to produce silver? Ag2O(s) → 2 Ag(s) + 1/2 O(g) ΔG° = 11.2 kJ/mol

A) Ag(s) + 1/2 Br2 → AgBr(s) ΔG° = 96.9 kJ/mol
B) C + 1/2 O2 → CO ΔG° = -137.2 kJ/mol
C) N + 1/2 O2 → NO ΔG° = 149.3 kJ/mol
D) N + O2 → NO2 ΔG° = 51.3 kJ/mol
E) C + 2 S → CS2(l) ΔG° = 65.3 kJ/mol

Question 59

Which of the following quantities for an element has a value of zero in the standard state? I) ΔH°f
II) ΔG°f
III) S°

A) I only
B) II only
C) III only
D) I and II
E) I, II, and III

Question 60

For the vaporization of water in an open system at 25°C and 1 atm, which of the following is correct?

A) The reaction is entropy driven.
B) The reaction is enthalpy driven.
C) The reaction is not spontaneous.
D) ΔG°rxn = 0

Question 61

Calculate ΔG° for the reaction Cu(s) + H2O(g) → CuO(s) + H2(g) at 500K. Cu(s) 0 33.3 H2O(g) -241.8 188.7
CuO(s) -155.2 43.5
H2(g) 0 130.6

A) 231.8 kJ
B) -135.4 kJ
C) -58.6 kJ
D) 110.6 kJ
E) 86.74 kJ

Question 62

If the enthalpy of vaporization of chloromethane, CH3Cl, is 21.5 kJ/mol at the normal boiling point, 249 K, calculate ΔS°vap.

A) 86.3 J mol-1 K-1
B) 5.35 J mol-1 K-1
C) 11.6 J mol-1 K-1
D) 896 J mol-1 K-1

Question 63

What is ΔG°rxn? 2 O3(g) → 3 O2(g)
ΔGf° (J/mol K) 163.2 0

A) 326.2 kJ
B) -326.4 kJ
C) -163.2 kJ
D) 163.2 kJ
E) 54.4 kJ

Question 64

For the reaction I2(s) + Cl2(g) → 2 ICl(g) ΔH = 36 kJ and ΔS = 158.8 J/K at 25 °C. Calculate ΔG for the process at 25 °C.

A) -11.3 kJ
B) -4730 kJ
C) -393 kJ
D) 32 kJ
E) 83.3 kJ

Question 65

What is ΔG° at 25°C? CO2(g) → CO2(aq) ΔH° = -19.4 kJ ΔS° = 92.3 J/K

A) 2.1 kJ
B) -46.9 kJ
C) -17.1 kJ
D) -19.5 kJ
E) -21.7 kJ

Question 66

Consider the following reaction: 4 NH3(g) + 7 O2(g) → 4 NO2(g) + 6 H2O (l)
ΔG°f -16.7 0.0 51.8 -237.2 kJ/mol
What is ΔG° for this reaction in kJ?

A) -1282
B) -1149
C) -169
D) 169
E) 1149

Question 67

Consider the following reaction. S2Cl2(g) + 2 OCl2(g) → 2 SOCl2(g) + Cl2(g)
ΔG°f -32 97.9 -320 0.0 kJ/mol
What is ΔG° for this reaction in kJ?

A) -804
B) -476
C) -386
D) -413
E) -799

Question 68

Consider the following reaction: C(g) + 2 H2(g) → CH4(g)
S° 5.69 130.58 186.19 J/mol∙deg
What is ΔS° for the above reaction in J/mol∙deg?

A) -49.9 J/mol∙deg
B) 49.9 J/mol∙deg
C) 80.7 J/mol∙deg
D) 115.2 J/mol∙deg
E) -80.7 J/mol∙deg

Question 69

Calculate the entropy change for methanol at its normal boiling point of 64.5°C. ΔH° = 38.0 kJ/mol.

A) 0.589 kJ/mol ∙ K
B) 0.112 kJ/mol ∙ K
C) 589 kJ/mol ∙ K
D) 112 kJ/mol ∙ K
E) 0.589 × 10-2 kJ/mol ∙ K

Question 70

What is ΔG°rxn? CO(g) + 2 H2(g) → CH3OH(g)
ΔGf° (J/mol K) -137.2 0 -162.0

A) -24.8 kJ
B) -299.2 kJ
C) +24.8 kJ
D) 149.6 kJ
E) +299.2 kJ

Question 71

Consider the reaction: 3 N2(g) + 2 O3(g) → 6 NO(g) ΔHf° 0.00 142.26 90.37 kJ/mol
S° 191.5 237.7 210.6 J/mol K
What is ΔG°rxn for this reaction in kJ at 500 K?

A) 93 kJ
B) 151 kJ
C) 365 kJ
D) -1.00 × 105 kJ
E) 441 kJ

Question 72

Consider the following reaction: C3H4(g) + 2 H2(g) → C3H8(g)
S° 266.9 130.6 269.9 J/mol∙deg
What is ΔS° in J/mol∙deg?

A) 127.6 J/mol∙deg
B) -127.6 J/mol∙deg
C) 3.0 J/mol∙deg
D) -258.2 J/mol∙deg
E) -3.0 J/mol∙deg

Question 73

Consider the following reaction: NH3(g) + HCl(g) → NH4Cl(s)
S° 192.51 186.69 94.56 J/mol∙deg
What is ΔS° for this reaction in J/mol∙deg?

A) -284.6 J/mol∙deg
B) 284.6 J/mol∙deg
C) -92.3 J/mol∙deg
D) 94.6 J/mol∙deg
E) 92.3 J/mol∙deg

Question 74

What is ΔG° at 25°C? CO(g) + 2 H2(g) → CH3OH(g) ΔH° = -90.7 kJ ΔS° = -221 J/K

A) -90.9 kJ
B) -24.8 kJ
C) -156.6 kJ
D) -96.2 kJ
E) -85.2 kJ

Question 75

What is ΔG°rxn? N2O4(g) → 2 NO2(g)
ΔGf° (J/mol K) 97.8 51.3

A) 149.1 kJ
B) -4.8 kJ
C) -46.5 kJ
D) 4.8 kJ
E) 46.5 kJ

Question 76

What is ΔG° at 25°C? N2O4(g) → 2 NO2(g) ΔH° = 58.03 kJ ΔS° = 176.7 J/K

A) 58.21 kJ
B) 62.45 kJ
C) 53.6 kJ
D) 5.37 kJ
E) 111 kJ

Question 77

What is ΔG° at 25 °C? CaCO3(s) → CaO(s) + CO2(g) ΔH° = 177.8 kJ ΔS° = 160.7 J/K

A) 1779 kJ
B) 173.8 kJ
C) 225.7 kJ
D) 181.8 kJ
E) 129.9 kJ

Question 78

What is ΔG° at 25°C? 2O3(g) → 3 O2(g) ΔH° = -284 kJ ΔS° = 139 J/K

A) -145 kJ
B) -243 kJ
C) -325 kJ
D) -281 kJ
E) -287 kJ

Question 79

What is ΔG°rxn? CaCO3(s) → CaO(s) + CO2(g)
ΔGf° (J/mol K) -1128 -604 -394.4

A) 1338 kJ
B) 918 kJ
C) -130 kJ
D) -918 kJ
E) 130 kJ

Question 80

For the reaction, 2 O3(g) → 3 O2(g)
S° (J/mol K) 238.8 205.0
What is ΔS°rxn?

A) 137.4 J/mol K
B) -137.4 J/mol K
C) 33.8 J/mol K
D) 171.2 J/mol K
E) -33.8 J/mol K