Deck 20: Thermodynamics: Entropy, Free Energy, and Reaction Direction

Question 1

Which of the following is always true for an exothermic process?

A)q _sys > 0, Δ S _surr < 0
B)q _sys < 0, Δ S _surr > 0
C)q _sys < 0, Δ S _surr < 0
D)q _sys > 0, Δ S _surr > 0
E)w < 0

Answer 1

q _sys < 0, Δ S _surr > 0

Question 2

A certain process has ΔS_univ > 0 at 25°C. What does one know about the process?

A)It is exothermic.
B)It is endothermic.
C)It is spontaneous at 25°C.
D)It will move rapidly toward equilibrium.
E)None of these choices are correct.

Answer 2

It is spontaneous at 25°C.

Question 3

Which of the following should have the greatest molar entropy at 298 K?

A)CH ₄( g)
B)H ₂O( l)
C)NaCl( s)
D)N ₂O ₄( g)
E)H ₂( g)

Answer 3

N ₂O ₄( g)

Question 4

As a chemical reaction proceeds toward equilibrium, the free energy of the system decreases.

Question 5

Which of the following values is based on the Third Law of Thermodynamics?

A)Δ H° _f = 0 for Al( s)at 298 K
B)Δ G° _f = 0 for H ₂( g)at 298 K
C)S° = 51.446 J/(mol·K)for Na( s)at 298 K
D)q _sys < 0 for H ₂O( l)→ H ₂O(s)at 0°C
E)None of these choices are correct.

Question 6

Under a given set of conditions, all microstates of a system are equally probable.

Question 7

The free energy of a perfect crystal at absolute zero, is zero.

Question 8

Which of the following is always true for an endothermic process?

A)q _sys > 0, Δ S _surr < 0
B)q _sys < 0, Δ S _surr > 0
C)q _sys < 0, Δ S _surr < 0
D)q _sys > 0, Δ S _surr > 0
E)w < 0

Question 9

For any reaction, if ΔG° > 0, then K < 1.

Question 10

The higher the pressure of a gas sample, the greater is its entropy.

Question 11

In some spontaneous processes, the entropy of the surroundings decreases.

Question 12

The term microstate refers to the energy state of a single molecule in a system of many molecules.

Question 13

In a spontaneous process, the entropy of the system always increases.

Question 14

For a reaction at equilibrium, ΔS_univ = 0.

Question 15

Which of the following is true for a system at equilibrium?

A)Δ S° _sys = Δ S° _surr
B)Δ S° _sys = −Δ S° _surr
C)Δ S° _sys = Δ S° _surr = 0
D)Δ S° _univ > 0
E)None of these choices are correct.

Question 16

The entropy of one mole of oxygen gas in a 0.5-L container is less than it would be in a 22.4-L container at the same temperature.

Question 17

For a given reaction, a change in the pressure may result in a change in the sign of ΔG.

Question 18

Which of the following is true for pure oxygen gas, O₂(g) at 25°C?

A)Δ H° _f > 0
B)Δ H° _f < 0
C)Δ G° _f > 0
D)Δ G° _f < 0
E)S° > 0

Question 19

Which of the following results in a decrease in the entropy of the system?

A)O ₂( g), 300 K → O ₂( g), 400 K
B)H ₂O( s), 0°C → H ₂O( l), 0°C
C)N ₂( g), 25°C → N ₂( aq), 25°C
D)NH ₃( l), −34.5°C → NH ₃( g), −34.5°C
E)2H ₂O ₂( g)→ 2H ₂O( g)+ O ₂( g)

Question 20

Which of the following is necessary for a process to be spontaneous?

A)Δ H _sys < 0
B)Δ S _sys > 0
C)Δ S _surr < 0
D)Δ S _univ > 0
E)Δ G _sys = 0

Question 21

Which relationship or statement best describes ΔS° for the following reaction? KCl(s) → K⁺(aq) + Cl⁻(aq)

A)Δ S° ≈ 0
B)Δ S° < 0
C)Δ S° > 0
D)Δ S° = Δ H°/ T
E)More information is needed to make a reasonable prediction.

Question 22

In which one of these pairs will the entropy of the first substance be greater than that of the second? Assume P and T are the same for each pair, unless stated otherwise.

A)1 mole of F ₂( g); 1 mole of Cl ₂( g)
B)1 mole of I ₂( s); 1 mole of I ₂( g)
C)1 mole of CaCO ₃( s); 1 mole of CaO( s)plus 1 mole of CO ₂( g)
D)1 mole of H ₂( g)at 25°C; 1 mole of H ₂( g)at 50°C
E)1 mole of O ₃( g); 1 mole of O ₂( g)

Question 23

Which relationship or statement best describes ΔS° for the following reaction? 2NH₃(g) + 2ClF₃(g) → 6HF(g) + N₂(g) + Cl₂(g)

A)Δ S° ≈ 0
B)Δ S° < 0
C)Δ S° > 0
D)Δ S° = Δ H°/ T
E)More information is needed to make a reasonable prediction.

Question 24

Which of the following pairs has the member with the greater molar entropy listed first? All systems are at 25°C.

A)CO( g), CO ₂( g)
B)NaCl( s), NaCl( aq)
C)H ₂S( g), H ₂S( aq)
D)Li( s), Pb( s)
E)H ₂( g), H ₂O( g)

Question 25

Which one of the following phase changes decreases the entropy of the system?

A)Melting
B)Heating a gas
C)Vaporization
D)Condensation
E)Sublimation

Question 26

Which relationship or statement best describes ΔS° for the following reaction? O₃(g) + NO(g) → O₂(g) + NO₂(g)

A)Δ S° ≈ 0
B)Δ S° < 0
C)Δ S° > 0
D)Δ S° = ΔH°/T
E)More information is needed to make a reasonable prediction.

Question 27

You are given pure samples of ammonia, NH₃(g), and nitrogen trifluoride, NF₃(g). What prediction would you make concerning their standard molar entropies at 298 K?

A)S° _ammonia > S° _{nitrogen trifluoride}
B)S° _ammonia < S° _{nitrogen trifluoride}
C)S° _ammonia ≈ S° _{nitrogen trifluoride}
D)Other conditions need to be specified before a reliable prediction can be made.
E)Even if more conditions are specified, a reliable prediction cannot be made.

Question 28

Which relationship best describes ΔS° for the following reaction? 8H₂(g) + S₈(s) → 8H₂S(g)

A)Δ S° = Δ H°
B)Δ S° = Δ H°/ T
C)Δ S° ≈ 0
D)Δ S° < 0
E)Δ S° > 0

Question 29

Which, if any, of the following processes is spontaneous under the specified conditions?

A)H ₂O( l)→ H ₂O( s)at 25°C
B)CO ₂( s)→ CO ₂( g)at 0°C
C)2H ₂O( g)→ 2H ₂(g)+ O ₂( g)
D)C(graphite)→ C(diamond)at 25°C and 1 atm pressure
E)None of these choices are correct.

Question 30

You are given pure samples of ethane, C₂H₆(g), and toluene, C₇H₈(l). What prediction would you make concerning their standard molar entropies at 298 K?

A)S° _ethane > S° _toluene
B)S° _ethane < S° _toluene
C)S° _ethane ≈ ( S° _toluene)÷ 3
D)S° _ethane ≈ S° _toluene
E)Since toluene is much more complex than ethane, but ethane is in the gas phase while toluene is a liquid, any of these predictions can be confidently made without further information or calculations.

Question 31

When a sky diver free-falls through the air, the process is

A)non-spontaneous because he is accelerating due to the force applied by gravity.
B)non-spontaneous because he is losing potential energy.
C)non-spontaneous, if he had planned the jump for two weeks.
D)spontaneous.
E)in equilibrium.

Question 32

Which relationship or statement best describes ΔS° for the following reaction? 2H₂S(g) + 3O₂(g) → 2H₂O(g) + 2SO₂(g)

A)Δ S° ≈ 0
B)Δ S° < 0
C)Δ S° > 0
D)Δ S° = Δ H°/ T
E)More information is needed to make a reasonable prediction.

Question 33

Which relationship or statement best describes ΔS° for the following reaction? C₂H₅OH(l) + 3O₂(g) → 2CO₂(g) + 3H₂O(l)

A)Δ S° ≈ 0
B)Δ S° < 0
C)Δ S° > 0
D)Δ S° = Δ H°/ T
E)More information is needed to make a reasonable prediction.

Question 34

Which relationship or statement best describes ΔS° for the following reaction? Pb(s) + Cl₂(g) → PbCl₂(s)

A)Δ S° ≈ 0
B)Δ S° < 0
C)Δ S° > 0
D)Δ S° = Δ H°/T
E)More information is needed to make a reasonable prediction.

Question 35

You are given pure samples of pentane, CH₃CH₂CH₂CH₂CH₃(l), and 1,3-pentadiene, CH₂=CHCH=CHCH₃(l). What prediction would you make concerning their standard molar entropies at 298 K?

A)S° _pentane > S° _{1, 3-pentadiene}
B)S° _pentane < S° _{1, 3-pentadiene}
C)S° _pentane ≈ S° _{1, 3-pentadiene}
D)S° _pentane = S° _{1, 3-pentadiene} + 2 S°H ₂
E)More information is needed to make reasonable predictions.

Question 36

Which relationship best describes ΔS° for the following reaction? CO(g) + H₂O(g) → CO₂(g) + H₂(g)

A)Δ S° = Δ H°
B)Δ S° = Δ H°/ T
C)Δ S° > 0
D)Δ S° < 0
E)Δ S° ≈ 0

Question 37

Which relationship or statement best describes ΔS° for the following reaction? HgS(s) + O₂(g) → Hg(l) + SO₂(g)

A)Δ S° ≈ 0
B)Δ S° < 0
C)Δ S° > 0
D)Δ S° = Δ H°/ T
E)More information is needed to make a reasonable prediction.

Question 38

Which relationship or statement best describes ΔS° for the following reaction? CaO(s) + CO₂(g) → CaCO₃(s)

A)Δ S° ≈ 0
B)Δ S° < 0
C)Δ S° > 0
D)Δ S° = Δ H°/ T
E)More information is needed to make a reasonable prediction.

Question 39

Which relationship or statement best describes ΔS° for the following reaction? BaCl₂(aq) + Na₂SO₄(aq) → BaSO₄(s) + 2NaCl(aq)

A)Δ S° ≈ 0
B)Δ S° < 0
C)Δ S° > 0
D)Δ S° = H°/ T
E)More information is needed to make a reasonable prediction.

Question 40

In which one of the following pairs will the first system have a higher entropy than the second? Assume P and T are the same for each pair, unless stated otherwise.

A)1 mole He( g); 1 mole Kr( g)
B)1 mole O ₂( g); 2 mole O( g)
C)1 mole CH ₄( g); 1 mole C ₂H ₆( g)
D)1 mole Xe( g)at 1 atmosphere; 1 mole Xe( g)at 0.5 atmosphere
E)20 one-dollar bills distributed randomly among 20 people; 20 one-dollar bills distributed randomly among 10 people

Question 41

For a process with ΔS < 0, which one of the following statements is correct?

A)The process will definitely be spontaneous if ΔH < 0.
B)The process will be definitely be spontaneous if Δ H < TΔ S.
C)The process can never be spontaneous.
D)The process will definitely be spontaneous, regardless of Δ H.
E)The process will definitely be spontaneous if Δ S _surr > 0.

Question 42

Which one of the following changes of state increases the entropy of the system?

A)Condensation
B)Cooling a gas
C)Freezing
D)Crystallization
E)Sublimation

Question 43

Consider the following quantities used in thermodynamics: E, H, q, w, S, G. How many of them are state functions?

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

Question 44

Calculate ΔS° for the combustion of propane. C₃H₈(g) + 5O₂(g) → 3CO₂(g) + 4H₂O(g)

A)−100.9 J/K
B)−72.5 J/K
C)72.5 J/K
D)100.9 J/K
E)877.5 J/K

Question 45

Given: H₂O(l) → H₂O(s) ΔH° = −6.02 kJ at 273K Calculate the entropy change of the surroundings (ΔS_surr) when one mole of water freezes at 0°C and a pressure of one atmosphere.

A)22.1 J/K
B)−22.1 J/K
C)397 J/K
D)−397 J/K
E)0.022 J/K

Question 46

Calculate ΔS° for the reaction 2Cl₂(g) + SO₂(g) → SOCl₂(g) + Cl₂O(g)

A)−118.2 J/K
B)−104.8 J/K
C)104.8 J/K
D)118.2 J/K
E)1270.0 J/K

Question 47

Calculate ΔS° for the reaction SiCl₄(g) + 2Mg(s) → 2MgCl₂(s) + Si(s)

A)−254.96 J/K
B)−198.02 J/K
C)198.02 J/K
D)254.96 J/K
E)471.86 J/K

Question 48

For a chemical reaction to be spontaneous only at high temperatures, which of the following conditions must be met?

A)Δ S° > 0, Δ H° > 0
B)Δ S° > 0, Δ H° < 0
C)Δ S° < 0, Δ H° < 0
D)Δ S° < 0, Δ H° > 0
E)Δ G° > 0

Question 49

For a chemical reaction to be non-spontaneous at any temperature, which of the following conditions must be met?

A)Δ S° > 0, Δ H° > 0
B)Δ S° > 0, Δ H° < 0
C)Δ S° < 0, Δ H° < 0
D)Δ S° < 0, Δ H° > 0
E)All reactions are spontaneous at some temperature.

Question 50

In order for a process to be spontaneous,

A)Δ H must be less than zero.
B)Δ S must be greater than zero.
C)Δ G must be greater than zero.
D)it should be rapid.
E)Δ S _sys + Δ S _surr must be greater than zero.

Question 51

For a chemical reaction to be spontaneous only at low temperatures, which of the following conditions must be met?

A)Δ S° > 0, Δ H° > 0
B)Δ S° > 0, Δ H° < 0
C)Δ S° < 0, Δ H° < 0
D)Δ S° < 0, Δ H° > 0
E)Δ G° > 0

Question 52

Which of the following conditions will ensure that a chemical reaction will definitely proceed in the forward direction, toward products?

A)Δ H > 0
B)Δ H < 0
C)Δ S _sys > 0
D)Δ S _surr > Δ S _sys
E)Δ S > Δ H/ T

Question 53

For a chemical reaction to be spontaneous at all temperatures, which of the following conditions must be met?

A)Δ S° > 0, Δ H° > 0
B)Δ S° > 0, Δ H° < 0
C)Δ S° < 0, Δ H° < 0
D)Δ S° < 0, Δ H° > 0
E)It is not possible for a reaction to be spontaneous at all temperatures.

Question 54

The second law of thermodynamics tells us that

A)the entropy of the universe is constant.
B)entropy is neither created nor destroyed.
C)the universe proceeds toward a state of lower entropy.
D)the universe proceeds toward a state of higher entropy.
E)the universe cannot create entropy.

Question 55

Elemental boron can be formed by reaction of boron trichloride with hydrogen. BCl₃(g) + 1.5H₂(g) → B(s) + 3HCl(g)
If ΔS° = 80.3 J/K for the reaction above, what is S° for BCl₃(g)?

A)−18.2 J/K·mol
B)18.2 J/K·mol
C)290.1 J/K·mol
D)355.4 J/K.mol
E)450.6 J/K·mol

Question 56

A certain process has ΔH° > 0, ΔS° < 0, and ΔG° > 0. The values of ΔH° and ΔS° do not depend on the temperature. Which of the following is a correct conclusion about this process?

A)It is non-spontaneous at all T.
B)It is spontaneous at high T.
C)It is spontaneous at low T.
D)It is spontaneous at all T.
E)None of these choices are correct.

Question 57

In order for a process to be spontaneous,

A)the entropy of the system must increase.
B)the entropy of the surroundings must increase.
C)the entropy of the universe must decrease.
D)the entropy of the surroundings must decrease.
E)the entropy change of the surroundings plus the entropy change of the system must be positive.

Question 58

A sample of water is heated at a constant pressure of one atmosphere. Initially, the sample is ice at 260 K, and at the end the sample consists of steam at 400 K. In which of the following 5K temperature intervals would there be the greatest increase in the entropy of the sample?

A)From 260 K to 265 K
B)From 275 K to 280 K
C)From 360 K to 365 K
D)370 K to 375 K
E)From 395 K to 400 K

Question 59

Calculate ΔS° for the reaction 4Cr(s) + 3O₂(g) → 2Cr₂O₃(s)

A)−548.1 J/K
B)−147.7 J/K
C)147.7 J/K
D)310.1 J/K
E)548.1 J/K

Question 60

Given: H₂O(l) → H₂O(g) ΔH° = 40.7 kJ at 373K What is the entropy change in the system (ΔS) when one mole of water vaporizes at 100°C and a pressure of one atmosphere?

A)407 J/K
B)−407 J/K
C)109 J/K
D)−109 J/K
E)J/K

Question 61

"A diamond is forever" is one of the most successful advertising slogans of all time. But is it true? For the reaction shown below, calculate the standard free energy change at 298K and determine whether or not a diamond is "forever". C(diamond) → C(graphite)
Data: ΔH_f°(diamond) = 1.895 kJ/mol; S°(diamond) = 2.337 J mol⁻¹K⁻¹; S°(graphite) = 5.740 J mol⁻¹K⁻¹.

A)Δ G° = 2.19 kJ; forever
B)Δ G° = −1.90 kJ; not forever
C)Δ G° = −2.90 kJ; not forever
D)Δ G° = 1.90 kJ; forever
E)Δ G° = < −1000 kJ; not forever

Question 62

Use the thermodynamic data at 298 K below to determine the K_sp for barium carbonate, BaCO₃ at this temperature.

A)5.86
B)6.30 × 10 ⁸
C)1.59 × 10 ⁻⁹
D)5.47 × 10 ⁻²¹
E)2.18 × 10 ⁻²⁷

Question 63

Use the given data at 298 K to calculate ΔG° for the reaction 2Cl₂(g) + SO₂(g) → SOCl₂(g) + Cl₂O(g)

A)129.3 kJ
B)133.6 kJ
C)196.0 kJ
D)199.8 kJ
E)229.6 kJ

Question 64

What is the free energy change, ΔG°, for the equilibrium between hydrogen iodide, hydrogen, and iodine at 453°C? K_c = 0.020 2HI(g) ⇄ H₂(g) + I₂(g)

A)6.4 kJ
B)8.8 kJ
C)15 kJ
D)19 kJ
E)24 kJ

Question 65

Consider the figure that shows ΔG° for a chemical process plotted against absolute temperature. Which one of the following is an incorrect conclusion, based on the information in the diagram?

A)Δ H° > 0
B)Δ S° > 0
C)The reaction is spontaneous at high temperatures.
D)Δ S° increases with temperature while Δ H° remains constant.
E)There exists a certain temperature at which Δ H° = TΔ S°.

Question 66

The temperature at which the following process reaches equilibrium at 1.0 atm is the normal melting point for phosphoric acid. H₃PO₄(s)⇄ H₃PO₄(l)
Use the following thermodynamic information at 298 K to determine this temperature.

A)286 K
B)305 K
C)315 K
D)347 K
E)3170 K

Question 67

Sulfuryl dichloride is formed when sulfur dioxide reacts with chlorine. The data refer to 298 K. SO₂(g) + Cl₂(g) → SO₂Cl₂(g)
What is the value of ΔG° for this reaction at 600 K?

A)−162.8 kJ
B)−40.1 kJ
C)−28.4 kJ
D)28.4 kJ
E)162.8 kJ

Question 68

Iron(III) oxide can be reduced by carbon monoxide. Fe₂O₃(s) + 3CO(g) ⇄ 2Fe(s) + 3CO₂(g)
Use the following thermodynamic data at 298 K to determine the equilibrium constant at this temperature.

A)7.0 × 10 ⁻⁶
B)1.3 × 10 ⁻³
C)2.2 × 10 ⁴
D)1.4 × 10 ⁵
E)> 2.0 × 10 ⁵

Question 69

Hydrogen sulfide decomposes according to the following reaction 2H₂S(g) → 2H₂(g) + S₂(g)
For this reaction at 298K ΔS° = 78.1 J/K, ΔH° = 169.4 kJ, and ΔG° = 146.1 kJ. What is the value of ΔG° at 900 K?

A)−69881 kJ
B)48.4 kJ
C)99.1 kJ
D)240 kJ
E)441 kJ

Question 70

The temperature at which the following process reaches equilibrium at 1.0 atm is the normal boiling point of hydrogen peroxide. H₂O₂(l) ⇄ H₂O₂(g)
Use the following thermodynamic information at 298 K to determine this temperature.

A)120°C
B)144°C
C)196°C
D)418°C
E)585°C

Question 71

Calculate the equilibrium constant at 25°C for the reaction of methane with water to form carbon dioxide and hydrogen. The data refer to 25°C. CH₄(g) + 2H₂O(g) ⇄ CO₂(g) + 4H₂(g)

A)8.2 × 10 ¹⁹
B)0.96
C)0.58
D)1.2 × 10 ⁻²⁰
E)1.4 × 10 ⁻⁴⁶

Question 72

The reaction of methane with water to form carbon dioxide and hydrogen is nonspontaneous at 298 K. At what temperature will this system make the transition from nonspontaneous to spontaneous? The data refer to 298 K. CH₄(g) + 2H₂O(g) ⇄ CO₂(g) + 4H₂(g)

A)658 K
B)683 K
C)955 K
D)1047 K
E)1229 K

Question 73

Calculate ΔG° for the reaction of ammonia with fluorine. 2NH₃(g) + 5F₂(g) → N₂F₄(g) + 6HF(g)

A)179.1 kJ
B)−179.1 kJ
C)1539.7 kJ
D)−1539.7 kJ
E)None of these choices are correct.

Question 74

Elemental boron can be formed by reaction of boron trichloride with hydrogen. BCl₃(g) + 1.5H₂(g) → B(s) + 3HCl(g)
Calculate ΔG° for the reaction.

A)−293.4 kJ
B)293.4 kJ
C)−102.8 kJ
D)102.8 kJ
E)None of these choices are correct.

Question 75

Calculate ΔG° for the combustion of propane. C₃H₈(g) + 5O₂(g) → 3CO₂(g) + 4H₂O(g)

A)−2073.1 kJ
B)−1387.3 kJ
C)−598.5 kJ
D)598.5 kJ
E)2073.1 kJ

Question 76

Nitric oxide reacts with chlorine to form NOCl. The data refer to 298 K.2NO(g) + Cl2(g) → 2NOCl(g) What is the value of ΔG° for this reaction at 550 K?

A)-143.76 kJ
B)-78.78 kJ
C)-22.24 kJ
D)-10.56 kJ
E)66600 kJ

Question 77

Consider the figure that shows ΔG° for a chemical process plotted against absolute temperature. From this plot, it is reasonable to conclude that

A)Δ H° > 0, Δ S° > 0
B)Δ H° > 0, Δ S° < 0
C)Δ H° < 0, Δ S° > 0
D)Δ H° < 0, Δ S° < 0
E)None of these choices are correct.

Question 78

Calculate ΔG° for the reaction SiCl₄(g) + 2Mg(s) → 2MgCl₂(s) + Si(s)

A)566.60 kJ
B)50.38 kJ
C)25.19 kJ
D)−25.19 kJ
E)−566.60 kJ

Question 79

Consider the figure that shows ΔG° for a chemical process plotted against absolute temperature. From this plot, it is reasonable to conclude that

A)Δ H° > 0, Δ S° > 0
B)Δ H° > 0, Δ S° < 0
C)Δ H° < 0, Δ S° > 0
D)Δ H° < 0, Δ S° < 0
E)None of these choices are correct.

Question 80

A reaction is proceeding toward equilibrium. At a certain stage, the concentrations of reactants and products are such that ΔG = ΔG°. What conclusion can reasonably be drawn about the reaction at this time?

A)K > Q
B)K < Q
C)K = Q
D)K = 1
E)Q = 1