Deck 14: Thermodynamics: Spontaneous Processes, Entropy, and Free Energy

Question 1

"S_sys" can be directly related to the heat q. Which of A-D is not true regarding this relationship? If all are true, select E.

A) "S_sys" can always be determined from the heat transferred during the actual process.
B) For a reversible spontaneous endothermic process, both q and "S_sys" will be positive.
C) The more heat that is transferred, the larger the magnitude of the entropy change.
D) The higher the temperature at which heat is transferred, the lower the entropy change.
E) All of the above are true.

Answer 1

"S_sys" can always be determined from the heat transferred during the actual process.

Question 2

Which of the following processes are spontaneous?
(I)Iron in the open air rusts.
(II)Liquid water in a freezer turns to ice.
(III)A spark ignites a mixture of propane and air.

A) I only
B) I and II only
C) I and III only
D) II and III only
E) I, II, and III are all spontaneous.

Answer 2

I, II, and III are all spontaneous.

Question 3

In a spontaneous process, the entropy of the universe ___________

A) increases always.
B) decreases always.
C) does not change.
D) may decrease if the entropy of the system decreases sufficiently.
E) may decrease if the entropy of the system increases sufficiently.

Answer 3

increases always.

Question 4

When you increase the volume of a gas, the energy separation between microstates __________

A) increases.
B) decreases.
C) remains unchanged.
D) becomes infinite.
E) disappears.

Question 5

Of the three modes of molecular motion-vibration, rotation, and translation-which requires the greatest amount of energy to cause an excitation from the ground state to the first excited state?

A) vibration
B) rotation
C) translation
D) They all require the same amount of energy.
E) None, as quantized energy states do not apply to these motions.

Question 6

In a spontaneous process, which of the following always increases?

A) the entropy of the system
B) the entropy of the surroundings
C) the entropy of the universe
D) the entropy of the system and the universe
E) the entropy of the system, surroundings and the universe

Question 7

Which, if any, of A through D is not true of entropy? If they are all true, select E.

A) It is a measure of the distribution of energy in a system at a specific temperature.
B) It is a measure of the number of accessible microstates in a pure substance.
C) It is a property of the universe that increases during a spontaneous process.
D) It is a property of a system that may increase or decrease during a spontaneous process.
E) All of the above are true statements.

Question 8

The entropy change in a system (S_sys) during a spontaneous process must be __________

A) greater than zero.
B) less than zero.
C) equal to zero.
D) greater than or equal to zero.
E) greater than, less than, or equal to zero.

Question 9

Boltzmann derived the relationship, S = k ln W where W is the __________

A) number of microstates.
B) vibrational energy.
C) kinetic energy.
D) Wentworth factor.
E) potential energy.

Question 10

Heat transfer from the system to the surroundings has a large effect on S_surr ___________

A) when the temperature of the surroundings is low.
B) when the temperature of the surroundings is high.
C) when the temperature of the system is low.
D) when the temperature of the system is high.
E) at any temperature as the amount of heat transferred is independent of temperature.

Question 11

During a spontaneous chemical reaction, it is found that "S_sys" < 0. This means __________

A) "S_surr" < 0 and its magnitude is < "S_sys".
B) "S_surr" < 0 and its magnitude is > "S_sys".
C) "S_surr" > 0 and its magnitude is < "S_sys".
D) "S_surr" > 0 and its magnitude is > "S_sys".
E) an error has been made, as S_sys > 0 by necessity for a spontaneous process.

Question 12

The entropy change of the surroundings, S_surr, is related to heat transfer q with respect to the system and temperature T by __________

A) -q/T_sys = S_surr.
B) +q/T_sys = S_surr.
C) -q/T_surr = S_surr.
D) q/T_surr = S_surr.
E) None of these, unless the system undergoes a reversible process.

Question 13

What types of motion does a molecule of chlorine have?

A) translational, rotational, vibrational
B) kinetic energy and potential energy
C) microstate and macrostate
D) Boltzmann and non-Boltzmann
E) all of the above

Question 14

Which of the following states of motion have the highest number of occupied excited states at room temperature-rotational, vibrational, or translational?

A) rotational
B) vibrational
C) translational
D) The number of occupied excited states is the same for the three modes of motion.
E) None of these, as excited states do not apply to these motions.

Question 15

An oxygen molecule can have several different modes of motions. One type of motion is __________

A) kinetic energy.
B) potential energy.
C) vibrational.
D) elastic.
E) Boltzmann.

Question 16

Which of the following must be true for the microstates of a system?
(I)The energy of each microstate equals the energy of the system.
(II)The entropy of each microstate equals the entropy of the system.
(III)The number of microstates equals the entropy of the system.

A) I only
B) II only
C) III only
D) I and III only
E) I, II, and III are all true.

Question 17

Which of the following processes are reversible in the thermodynamic sense?
(I) Iron in the open air rusts.
(II) NaCl is dissolved in water and then recovered by the evaporation of the water.
(III) The ice in a mixture of ice and water at 0°C and 1 atm melts.

A) I only
B) II only
C) III only
D) II and III only
E) I, II and III are all reversible.

Question 18

According to the second law of thermodynamics, the change in the entropy of the universe (S_univ) during a spontaneous reaction is __________

A) zero.
B) negative.
C) positive.
D) less than the change in entropy of the system (S_sys).
E) greater than the change in entropy of the system (S_sys).

Question 19

Which of the following must be true for a spontaneous exothermic process?

A) only that S_sys < 0
B) only that S_sys > 0
C) both S_sys < 0 and the magnitude of S_sys < the magnitude of S_surr
D) both S_sys < 0 and the magnitude of S_sys > the magnitude of S_surr
E) either S_sys > 0 or S_sys < 0 and the magnitude of S_sys < the magnitude of S_surr

Question 20

The gas above the liquid in a sealed bottle of soda is primarily carbon dioxide. Carbon dioxide is also dissolved in the soda. When the distribution of carbon dioxide between the gas and liquid is at equilibrium, molecules of carbon dioxide in the gas phase can still dissolve in the liquid phase if they strike the surface and are captured. Similarly molecules of carbon dioxide can escape from the liquid phase. What is the entropy change of the universe, "S_univ", for the dissolution of carbon dioxide under these conditions?

A) "S_univ" < 0 because the dissolved carbon dioxide has fewer accessible states.
B)" S_univ" > 0 because the dissolved carbon dioxide has fewer accessible states.
C) "S_univ" = 0 because this is an equilibrium situation.
D) "S_univ" < 0 because the gas dissolves spontaneously.
E) "S_univ" > 0 because the gas dissolves spontaneously.

Question 21

At 0 K, the entropy of a perfect crystal is ___________

A) > 0.
B) = 0.
C) < 0.
D) > 0, = 0, or < 0, depending on the chemical structure of the crystal.
E) > 0 or = 0, depending on the chemical structure of the crystal.

Question 22

Which of the following will have the greatest standard molar entropy (S°)?

A) NH₃(g)
B) He(g)
C) C(s, graphite)
D) H₂O( )
E) CaCO₃(s)

Question 23

Care must be taken when dissolving solid pellets of sodium hydroxide (NaOH) in water as the temperature of the water can rise dramatically. Taking NaOH as the system, what can you deduce about the signs of the entropy change of the system (S_sys) and surroundings (S_surr) from this?

A) "S_sys" < 0 and "S_surr" < 0
B)" S_sys" < 0 and "S_surr" > 0
C) "S_sys" > 0 and "S_surr" < 0
D)" S_sys" > 0 and "S_surr" > 0
E) Nothing can be deduced from this limited information.

Question 24

Indicate which of the following has the highest entropy at 298 K.

A) 0.5 g of HCN
B) 1 mol of HCN
C) 2 kg of HCN
D) 2 mol of HCN
E) All of the above have the same entropy at 298 K.

Question 25

Which of the relationships A through D between the free energy change of a system and associated entropy changes is true?

A) "G_sys" = +T "S_system"
B) "G_sys" = -T "S_system"
C) "G_sys" = +T "S_universe"
D) "G_sys" = -T "S_surroundings"
E) "G_sys" = -T "S_universe"

Question 26

Consider a closed container containing a 1 M solution of HCl above which is air that contains water vapor at its equilibrium vapor pressure. Assume the pressure of the air and water vapor is 1 bar and the temperature of the system is 298 K. Which of the following are in their thermodynamic standard state?
(I)The liquid water
(II)The HCl solution
(III)The water vapor

A) I only
B) II only
C) III only
D) I and II only
E) I, II, and III are all in their standard state.

Question 27

Perfect crystals of carbon monoxide (CO) are difficult to prepare because the very small dipole moment allows a few molecules to align in a pattern like CO OC CO instead of CO CO CO. If such crystals were cooled to 0 K, what would be the value of their absolute entropy?

A) > 0
B) = 0
C) < 0
D) > 0, = 0, or < 0, depending on how carefully it was cooled
E) > 0 or = 0, depending on how carefully it was cooled

Question 28

Which of the processes A-D will lead to a positive change in the entropy of the system? If all of these processes lead to a positive change in the entropy of the system, select E.

A) Sodium chloride crystals form as saltwater evaporates.
B) Helium gas escapes from the hole in a balloon.
C) Stalactites form in a cave.
D) Water freezes in a freezer.
E) All of these lead to a positive change in entropy of the system, as they are all spontaneous.

Question 29

Which of the following processes will lead to a decrease in the entropy of the system?

A) Salt crystals dissolve in water.
B) Air escapes from a hole in a balloon.
C) Iron and oxygen react to form rust.
D) Ice melts in your hand.
E) None of these lead to a negative change in the entropy of the system, as they are all spontaneous.

Question 30

The standard molar entropy of lead(II) bromide (PbBr₂) is 161 J/mol · K. What is the entropy of 2.45 g of PbBr₂?

A) +1.07 J/K
B) -1.07 J/K
C) +161 J/K
D) -161 J/K
E) 0 J/K

Question 31

The following figures represent distributions of two types of gas molecules between two containers connected by an open tube. In which figure is the entropy of the system maximized?

A)
B)
C)
D)

Question 32

The entropy of a NaCl crystal is __________

A) an intensive property and a state function.
B) an intensive property and a path function.
C) an extensive property and a state function.
D) an extensive property and a path function.
E) not appropriately described in terms of an intensive property, an extensive property, a state function, or a path function.

Question 33

Indicate which of the following has the lowest standard molar entropy (S°).

A) CH₄(g)
B) CH₃CH₂OH( )
C) H₂O(s)
D) Na(s)
E) He(g)

Question 34

The following figures represent distributions of gas molecules between two containers connected by an open tube. In which figure is the entropy of the system maximized?

A)
B)
C)
D)

Question 35

Indicate which one of the following reactions result in a positive S_sys.

A) AgNO₃(aq) + NaCl(aq)  AgCl(s) + NaNO₃(aq)
B) HCl(g) + H₂O( )  HCl(aq)
C) H₂(g) + I₂(g)  2 Hl(g)
D) C₂H₂O₂(g)  2 CO(g) + H₂(g)
E) H₂O(g)  H₂O(l)

Question 36

What is the entropy change to the surroundings when 1 mol of ice melts in someone's hand if the hand temperature is 32°C? Assume a final temperature for the water of 0°C. The heat of fusion of ice is 6.01 kJ/mol.

A) -188 J/K
B) -22.0 J/K
C) -19.7 J/K
D) +19.7 J/K
E) +188 J/K

Question 37

Which of the following graphs best depicts the entropy of a pure substance as the temperature is raised from its solid form through its liquid and gaseous forms?

A)
B)
C)
D)

Question 38

If 1 mol of ice melts at its melting point of 273 K, the entropy change for the ice is 22.0 J/K. If the ice melts in someone's hand at 34°C, what is the change in the entropy of the universe? Assume a final temperature for the water of 0°C. The enthalpy of fusion for ice is 6.01 kJ/mol.

A) +19.6 J/K
B) -19.6 J/K
C) +2.4 J/K
D) -2.4 J/K
E) +41.5 J/K

Question 39

Indicate which one of the following reactions results in a negative S_sys.

A) H₂O(g)  H₂O(s)
B) CaCO₃(s)  CaO(s) + CO₂(g)
C) CuSO₄ · 5H₂O(s)  CuSO₄(s) + 5H₂O(g)
D) 14O₂(g) + 3NH₄NO₃(s) + C₁₀H₂₂( )  3N₂(g) + 17H₂O(g) + 10CO₂(g)
E) CO₂(aq)  CO₂(g)

Question 40

Which of the following is in the correct order of standard state entropy?
(I)Diamond < graphite
(II)Liquid water < solid water
(III)NH₃ < H₂

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

Question 41

A reaction with a low enthalpy of reaction value is not spontaneous at low temperature but becomes spontaneous at high temperature. What are the signs for H° and S°, respectively?

A) +, -
B) -, -
C) -, +
D) +, +
E) Insufficient data is provided to answer this question.

Question 42

Processes are always spontaneous when __________ (H and S refer to the system).

A) "H" > 0 and "S" < 0
B)"H" < 0 and "S" < 0
C) "H" > 0 and "S" > 0
D) "H" < 0 and "S" > 0
E) None of these is true, as temperature must always be taken into account.

Question 43

At constant T and P, any reaction will be spontaneous if __________

A) 'G_sys' > 0
B) 'G_sys' < 0
C) 'S_sys" > 0
D)' S_sys" < 0
E) "H_sys' < 0

Question 44

If a reaction A  B has G > 0, then when the reaction is at equilibrium there will be __________

A) absolutely no B that is formed.
B) smaller quantities of B and larger quantities of A.
C) equal quantities of A and B.
D) large quantities of B and smaller quantities of A.
E) absolutely no A remaining.

Question 45

At what temperature does the Fe(s)  Fe(g) phase transition occur? H = 415.5 kJ/mol; S = 153.4 J/mol · K.

A) 2162°F
B) 2435°F
C) 4352°F
D) 4416°F
E) 2709°F

Question 46

Hydrochloric acid (HCl) reacts with sodium hydroxide (NaOH) to form sodium chloride (NaCl) and water. If H° = -56.13 kJ/mol and S° = 79.11 J/mol · K, what is G° for this reaction at 20°C?

A) -79.31 kJ/mol
B) -77.73 kJ/mol
C) -2.324  10⁴ kJ/mol
D) 79.31 kJ/mol
E) -1638 kJ/mol

Question 47

A reaction is at equilibrium at a given temperature and constant pressure when __________

A) "S_rxn" = 0.
B) "S " = 0.
C) "G_rxn = 0.
D)" G " = 0.
E) "H_rxn" = 0.

Question 48

The symbol G (CH₄, g) refers to which of the following reactions?

A) CH₄(l)  CH₄(g)
B) CH₄(g)  CH₄( )
C) CH₄(g)  C(g) + 4H(g)
D) C(g) + 4H(g)  CH₄(g)
E) C(s, graphite) + 2H₂(g)  CH₄(g)

Question 49

At body temperature, many proteins have a well-defined structure that is essential to their function. As the temperature is raised, however, the structure changes and the protein is no longer functional. This is referred to as protein denaturation. What can be deduced from this information about the signs of the enthalpy and entropy changes for denaturation?

A) "H" > 0 and "S" > 0
B) "H" > 0 and "S" < 0
C) "H" < 0 and "S" > 0
D) "H" < 0 and "S" < 0
E) There is insufficient information to deduce anything about the signs of H and S.

Question 50

Which of the following statements about equilibrium are true?
(I)G_sys = 0
(II)S_sys = 0
(III)S_universe = 0

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

Question 51

The equilibrium vapor pressure for benzene is 94.4 mm Hg. When liquid benzene is in equilibrium with its vapor, we must have __________

A) "G" = 0 and "G°" = 0
B) "G" = 0 and "G°" > 0
C) "G" = 0 and "G°" < 0
D) "G" > 0 and "G°" = 0
E) "G" < 0 and "G°" = 0

Question 52

The entropy of vaporization of water is 109.0 J/mol · K. What is the enthalpy of vaporization of water at its normal boiling point?

A) +10.90 kJ/mol
B) -40.66 kJ/mol
C) +3.42 kJ/mol
D) +40.66 kJ/mol
E) -10.90 kJ/mol

Question 53

Dinitrogen tetroxide (N₂O₄) decomposes to nitrogen dioxide (NO₂). If H° = 58.02 kJ/mol and S° = 176.1 J/mol · K, at what temperature are reactants and products in their standard states at equilibrium?

A) +56.5°C
B) +329.5°C
C) -272.7°C
D) +25.0°C
E) +98.3°C

Question 54

Hydrogen reacts with nitrogen to form ammonia (NH₃) according to the reaction 3H₂(g) + N₂(g)  2NH₃(g)
The value of H° is -92.38 kJ/mol, and that of S° is -198.2 J/mol · K. Determine G° at 25°C.

A) +5.897  10⁴ kJ/mol
B) +297.8 kJ/mol
C) -33.32 kJ/mol
D) -16.66 kJ/mol
E) +49.5 kJ/mol

Question 55

Which of the following are true for a reversible process at equilibrium?
(I)S_univ = 0
(II)S_sys = 0
(III)G_sys = 0

A) I only
B) II only
C) III only
D) I and III only
E) I, II, and III are all true.

Question 56

Benzene is a liquid under standard conditions. The standard free-energy change for the evaporation of liquid benzene to form benzene vapor is +5.2 kJ/mol. If liquid benzene is placed in an open container under standard conditions, __________

A) it will not evaporate.
B) it will partially evaporate with the equilibrium vapor pressure being less than 1 bar.
C) it will partially evaporate with the equilibrium vapor pressure being equal to 1 bar.
D) it will partially evaporate with the equilibrium vapor pressure being greater than 1 bar.
E) it will completely evaporate.

Question 57

The enthalpy and entropy of vaporization of ethanol are 38.6 kJ/mol and 109.8 J/mol · K, respectively. What is the boiling point of ethanol, in °C?

A) 352°C
B) 78.5°C
C) 2.84°C
D) 624°C
E) Not enough information is given to answer the question.

Question 58

The dissolution of ammonium nitrate in water is a spontaneous endothermic process. It is spontaneous because the system undergoes __________

A) a decrease in enthalpy.
B) an increase in entropy.
C) an increase in enthalpy.
D) a decrease in entropy.
E) an increase in free energy.

Question 59

Determine G_rxn for C₄H₁₀( ) + O₂(g)  4CO₂(g) + 5H₂O(g) given the following. Substance
G (J/mol · K)
C₄H₁₀( )
-15)0
CO₂(g)
-394.4
H₂O(g)
-228.57

A) -2705 kJ/mol
B) -608.0 kJ/mol
C) -1791 kJ/mol
D) -3457 kJ/mol
E) +608.0 kJ/mol

Question 60

The enthalpy of fusion for benzene is 127.40 kJ/kg, and its melting point is 5.5°C. What is the entropy change when 1 mole of benzene melts at 5.5°C?

A) 9.95 kJ/K
B) 35.7 J/K
C) 1809 J/K
D) 1.81 J/K
E) 127.40 kJ/K

Question 61

The standard entropy of diamond is 2.4 J/mol · K. Calculate the entropy per carbon atom in diamond and the number of microstates for each atom. Discuss the number of microstates in terms of the molecular motions accessible to each carbon atom.

Question 62

The standard molar enthalpy of fusion for xenon is 2.30 kJ mol^-1. Calculate the standard molar entropy for the freezing of liquid xenon given that its normal freezing point is -112°C.

Question 63

The standard entropy of N₂(g) is 191.5 J/mol · K. Calculate the entropy per nitrogen molecule and the number of microstates for each molecule. Discuss the number of microstates in terms of the molecular motions accessible to each molecule.

Question 64

The entropy of fusion for ice at 0°C and 1 atm is 22 J/mol · K. How many joules of heat are required to melt a typical ice cube at 0°C and 1 atm? Assume an ice cube is about 1 oz or 28
g.

Question 65

The heat of fusion for water is 333.6 J/g. What is the entropy change for the universe when 1.00 L of water at 0°C freezes at +5°C? Comment on the sign.

Question 66

What is a microstate and how are microstates quantitatively related to entropy?

Question 67

Determine the normal melting point of benzoic acid in degrees centigrade given the following data.
H = 18.02 kJ/mol
S = 45.56 J/mol · K

Question 68

Carbon monoxide has a very weak dipole moment. In the formation of solid carbon monoxide some molecules will be reversed in their orientation from C O - - - C O to C O - - - O C. What do you expect the absolute entropy of carbon monoxide solid to be at 0 K, and why?

Question 69

Carbon atoms can be found in a variety of elemental forms. At sufficiently high temperature, carbon is an atomic gas. At room temperature, both tetrahedral networks in diamond and trigonal planar networks in graphite can be found. Trigonal planar networks of carbon atoms are also found in Buckminsterfullerene (C₆₀). How does the standard entropy of these forms vary per mole of carbon?

Question 70

The change in standard molar entropy, S for the following reaction is 494.6 J/mol · K at 25C.
2KClO₃(s)  2KCl(s) + 3O₂(g)
What is the standard molar entropy of O₂(g) at 25C?
S°(KClO₃, s)= 143.1 J/mol · K
S°(KCl, s)= 82.6 J/mol · K

Question 71

Only one substance has a standard entropy of 0 J/K, and that is H⁺(aq). Why is this so?

Question 72

Considering the tabulated values for the thermodynamic properties of oxygen gas, why is the standard entropy nonzero but the standard enthalpy and free energy of formation are zero?

Question 73

What are the signs of H°, S°, and G° for the conversion of liquid water to ice at 10°C and 1 atm? Briefly explain each answer.

Question 74

Draw a graph of entropy versus temperature for a typical substance. Be sure to clearly label phases and phase transitions on the graph.

Question 75

Give an example of a spontaneous and a nonspontaneous chemical process and the sign of the entropy change for the universe for each.

Question 76

The heat of fusion for water is 333.6 J/g. What is the entropy change for the universe when 1.00 L of water at 0°C freezes at -5°C? Comment on the sign.

Question 77

What is the overall standard free-energy change for the following two reactions in terms of G₁ and G₂?
A + B  2C G = G₁
C + D  E G = G₂

Question 78

Hydrogen iodide can theoretically be made by the reaction of hydrogen gas and iodine by the following reaction.
H₂(g) + I₂(s)  2HI(g)
What temperature conditions are required for the formation of HI to be favored at standard pressure?
S°(H₂, g) = 130.6 J/mol · K
S°(I₂, s) = 116.1 J/mol · K
S°(HI, g) = 206.6 J/mol · K
H (HI, g) = 26.5 kJ/mol · K

Question 79

Name and state the first three laws of thermodynamics.