Deck 17: Thermodynamics: Spontaneous and Nonspontaneous Reactions and Processes

Question 1

What is the entropy change to the surroundings when 1 mol of ice melts in someone's hand if the hand temperature is 32 ^$\circ$ C? Assume a final temperature for the water of 0 ^$\circ$ 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)

Answer 1

(-19.7 J/K)

Question 2

For a chemical reaction that is not spontaneous, it is found that $\Delta$ S_sys < 0. Which of the following could not be true?

A)( $\Delta$ S_surr < 0 and its magnitude is less than $\Delta$ S_sys.)
B)( $\Delta$ S_surr > 0 and its magnitude is less than $\Delta$ S_sys.)
C)( $\Delta$ S_surr < 0 and its magnitude is greater than $\Delta$ S_sys.)
D)( $\Delta$ S_surr > 0 and its magnitude is greater than $\Delta$ S_sys.)
E)( $\Delta$ S_univ < 0)

Answer 2

( $\Delta$ S_surr > 0 and its magnitude is greater than $\Delta$ S_sys.)

Question 3

$\Delta$ S_sys can be directly related to the heat, q. Which of statements A-D is not true regarding this relationship?

A)( $\Delta$ S_sys can always be determined from the heat transferred during the actual process.)
B)For a reversible spontaneous endothermic process, both q and $\Delta$ 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 3

( $\Delta$ S_sys can always be determined from the heat transferred during the actual process.)

Question 4

Which of the following processes is/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 ^$\circ$ 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 5

The entropy change of the surroundings, $\Delta$ S_surr, is related to heat transfer, q, with respect to the system and temperature T by ________

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

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, the surroundings, and the universe

Question 7

According to the second law of thermodynamics, the change in the entropy of the universe ( $\Delta$ S_univ) during a spontaneous reaction is ________

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

Question 8

Heat transfer from the system to the surroundings has a large effect on $\Delta$ 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, because the amount of heat transferred is independent of temperature.

Question 9

The entropy change in a system ( $\Delta$ 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 10

Which of the following processes is/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.

Question 11

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 ^$\circ$ C, what is the change in the entropy of the universe? Assume a final temperature for the water of 0 ^$\circ$ 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 12

Care must be taken when dissolving solid pellets of sodium hydroxide (NaOH) in water, because 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 ( $\Delta$ S_sys) and surroundings ( $\Delta$ S_surr) from this?

A)( $\Delta$ S_sys < 0 and $\Delta$ S_surr < 0)
B)( $\Delta$ S_sys < 0 and $\Delta$ S_surr > 0)
C)( $\Delta$ S_sys > 0 and $\Delta$ S_surr < 0)
D)( $\Delta$ S_sys > 0 and $\Delta$ S_surr > 0)
E)Nothing can be deduced from this limited information.

Question 13

During a spontaneous chemical reaction, it is found that $\Delta$ S_sys < 0. This means ________

A)( $\Delta$ S_surr < 0 and its magnitude is < $\Delta$ S_sys.)
B)( $\Delta$ S_surr < 0 and its magnitude is < $\Delta$ S_sys.).
C)( $\Delta$ S_surr > 0 and its magnitude is > $\Delta$ S_sys.
D)( $\Delta$ S_surr > 0 and its magnitude is > $\Delta$ S_sys.)
E)an error has been made, because S_sys > 0 by necessity for a spontaneous process.

Question 14

During a spontaneous chemical reaction, it is found that $\Delta$ S_sys > 0. Which of the following could not be true?

A)( $\Delta$ S_surr < 0 and its magnitude is < $\Delta$ S_sys.)
B)( $\Delta$ S_surr > 0 and its magnitude is < $\Delta$ S_sys.)
C)( $\Delta$ S_surr < 0 and its magnitude is > $\Delta$ S_sys.)
D)( $\Delta$ S_surr > 0 and its magnitude is > $\Delta$ S_sys.)
E)( $\Delta$ _univ > 0)

Question 15

For a chemical reaction that is not spontaneous, it is found that $\Delta$ S_sys > 0. Which of the following could be true?

A)( $\Delta$ S_surr < 0 and its magnitude is less than $\Delta$ S_sys.)
B)( $\Delta$ S_surr > 0 and its magnitude is less than $\Delta$ S_sys.)
C)( $\Delta$ S_surr < 0 and its magnitude is greater than $\Delta$ S_sys.)
D)( $\Delta$ S_surr > 0 and its magnitude is greater than $\Delta$ S_sys.)
E)( $\Delta$ S_univ > 0)

Question 16

Which, if any, of statements A-D is not true of entropy?

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 17

In a spontaneous process, the entropy of the universe ________

A)always increases.
B)always decreases.
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.

Question 18

The entropy change in the surroundings ( $\Delta$ S_surr) 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 19

An ice cube at 0 ^$\circ$ C melts in a swimming pool at 25 ^$\circ$ C. What is the change in the entropy of the universe as a result? The ice cube was 2.00 inches on a side. Assume ice has a density of 0.917 g/cm³ and that the enthalpy of fusion of water is 6.01 kJ/mol.

A)( +3.1 J/K)
B)(-3.1 J/K)
C)0.0 J/K
D)(+12.3 J/K)
E)(-12.3 J/K)

Question 20

The enthalpy of fusion for benzene (C₆H₆) is 127.40 kJ/kg, and its melting point is 5.5 ^$\circ$ C. What is the entropy change when 1 mole of benzene melts at 5.5 ^$\circ$ C?

A)9.95 kJ/K
B)35.7 J/K
C)1,809 J/K
D)1.81 J/K
E)127.40 kJ/K

Question 21

When a molecule of ethylenediamine replaces two molecules of NH₃ in Co(NH₃) , the entropy of the system ________

A)increases.
B)decreases.
C)remains the same.
D)cannot be determined.
E)is irrelevant.

Question 22

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 is/are in its 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 states.

Question 23

Indicate which one of the following reactions most certainly results in a negative $\Delta$ S_sys.

A)
B)
C)
D)
E)

Question 24

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 such as CO OC CO instead of CO CO CO. If such disordered 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 25

Before class, students were distributed throughout a classroom. When the bell rang, all the students sat down at three tables in the center of the room. The entropy of the class ________

A)increased.
B)decreased.
C)remained the same.
D)cannot be determined.
E)is irrelevant.

Question 26

Indicate which one of the following reactions most certainly does not result in a decrease in entropy.

A)
B) )
C)
D)
E)

Question 27

Indicate which one of the following reactions results in a positive $\Delta$ S_sys.

A)
B)
C)
D)
E)

Question 28

The enthalpy of vaporization for toluene (C₇H₈) is 380.00 kJ/kg, and its boiling point is 110.6 ^$\circ$ C. What is the entropy change when 0.75 mole of toluene vaporizes at 110.6 ^$\circ$ C?

A)743 J/K
B)139 J/K
C)68.5 J/K
D)36.3 J/K
E)253 kJ/K

Question 29

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 30

Indicate which one of the following reactions results in a negative $\Delta$ S_sys.

A)
B)
C)
D)
E)

Question 31

Which of the following will have the greatest standard molar entropy (S ^$\circ$ )?

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

Question 32

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 33

Which of the processes A-D will lead to a positive change in the entropy of the system?

A)Sodium chloride crystals form as salt water 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, because they are all spontaneous.

Question 34

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 leads to a negative change in the entropy of the system, because they are all spontaneous.

Question 35

Before class, students were seated at three tables. When the school alarm went off suddenly, all the students distributed throughout the room to collect their belongings. The entropy of the class ________

A)increased.
B)decreased.
C)remained the same.
D)cannot be determined.
E)is irrelevant.

Question 36

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 37

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, $\Delta$ S_{uni v}, for the dissolution of carbon dioxide under these conditions?

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

Question 38

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 39

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

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

Question 40

Indicate which of the following has the largest standard molar entropy (S ^$\circ$ ).

A)CH₄(g)
B)CH₃CH₂OH(l )
C)CO₂(s)
D)Na(s)
E)NH₃(l )

Question 41

The standard molar entropy of magnesium fluoride (MgF₂) is 57.2 J/(mol . K). What is the entropy of 4.75 g of MgF₂?

A)(+4.36 J/K)
B)(-4.36 J/K)
C)(+272 J/K)
D)(-272 J/K)
E)0 J/K

Question 42

In an experiment, 1.00 atm of N₂(g) in a 10.0 L container at 25 ^$\circ$ C was reacted under standard state conditions with a stoichiometric quantity of H₂(g) to form ammonia: .
What is the entropy change for the reaction?

A)(-198.7 J/K)
B)(-81.5 J/K)
C)(-27.2 J/K)
D)(+81.5 J/K)
E)(+198.7 J/K)

Question 43

NO gas is converted to NO₂ gas according to the following reaction:
What is the standard entropy change when 0.5 mol of NO gas reacts with 0.5 mol of O₂ gas?

A)(-36.6 J/K)
B)(-175.7 J/K)
C)(-83.4 J/K)
D)(+83.4 J/K)
E)(+36.6 J/K)

Question 44

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 45

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 46

Indicate which of the following has the smallest standard molar entropy (S ^$\circ$ ).

A)NH₃(g)
B)H₂O(l)
C)Mg(s)
D)Hg(l )
E)Ar(g)

Question 47

The symbol $\Delta$ (CH₄, g) refers to which of the following reactions?

A)
B)
C)
D)
E)

Question 48

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

A)( $\Delta$ G_sys = +T $\Delta$ S_system)
B)( $\Delta$ G_sys = -T $\Delta$ S_system)
C)( $\Delta$ G_sys = +T $\Delta$ S_universe)
D)( $\Delta$ G_sys = -T $\Delta$ S_surroundings)
E)( $\Delta$ G_sys = -T $\Delta$ S_universe)

Question 49

The standard molar entropy of silver chloride (AgCl) is 96.2 J/(mol . K). What is the entropy of 1.78 g of AgCl?

A)(-1.19 J/K)
B)(+1.19 J/K)
C)(+96.2 J/K)
D)(-96.2 J/K)
E)0 J/K

Question 50

What is the entropy change if 4.500 g of CaCO₃(s) is placed in a container and allowed to decompose to CaO(s) and CO₂(g) according to the following reaction?

A)(+7.2 J/K)
B)(-160.5 J/K)
C)(+35.7 J/K)
D)(+160.5 J/K)
E)(+3.57 J/K)

Question 51

Determine the standard entropy of N₂(g) given the following information: $\Delta$ = -198.3 J/K

A)(-260.2 J/K)
B)(+260.2 J/K)
C)(+93.9 J/K)
D)(+191.5 J/K)
E)(-191.5 J/K)

Question 52

Determine $\Delta$ for given the following information:

A)(-41.10 J/K)
B)(-165.29 J/K)
C)(+398.75 J/K)
D)(+165.29 J/K)
E)(+41.10 J/K)

Question 53

What is the difference between $\Delta$ G and $\Delta$ G ^$\circ$ ?

A)( $\Delta$ G ^$\circ$ refers to the formation of a compound from its elements; $\Delta$ G can be defined for any reaction.)
B)( $\Delta$ G ^$\circ$ refers to the formation of a pure compound; $\Delta$ G can be defined for an impure compound.)
C)( $\Delta$ G ^$\circ$ refers to a reaction that goes to completion; $\Delta$ G is defined for a reaction that goes to any extent.)
D)( $\Delta$ G ^$\circ$ refers to the conversion of reactants in their standard state to products in their standard state; $\Delta$ G is defined for a reaction under any conditions.)
E)( $\Delta$ G ^$\circ$ refers to reactions of one mole quantities of reactants; $\Delta$ G is defined for any quantity of reactants.)

Question 54

Determine the entropy change for the reaction given the following information:

A)(-196.4 J/K)
B)(+196.4 J/K)
C)(-93.9 J/K)
D)(+93.9 J/K)
E)(+401.4 J/K)

Question 55

The symbol $\Delta$ (CH₃OH, l) refers to which of the following reactions?

A)
B)
C)
D)
E)

Question 56

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 57

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 58

What is the standard entropy change when 10.0 g of methane reacts with 10.0 g of oxygen?

A)(-121 J/K)
B)(-37.9 J/K)
C)(-242.6 J/K)
D)(-154.4 J/K)
E)(-16.8 J/K)

Question 59

Determine $\Delta$ for given the following information:

A)(-39.6 J/K)
B)0 J/K
C)(+39.6 J/K)
D)(-38.2 J/K)
E)(+38.2 J/K)

Question 60

If 3.500 g of Ni are reacted with excess oxygen to form nickel oxide (NiO) under standard state conditions, what is the entropy change for the reaction?

A)(-49.3 J/K)
B)(-24.7 J/K)
C)(-14.7 J/K)
D)(+49.3 J/K)
E)(-10.4 J/K)

Question 61

Given the following data relevant to the combustion of ethanol, determine the free energy of formation for liquid ethanol, C₂H₅OH. (C₂H₅OH, l) -930.7 kJ/mol (CO₂, g) -394.4 kJ/mol (H₂O, g) -105.6 kJ/mol

A)(-1,640.3 kJ/mol)
B)(-244.2 kJ/mol)
C)(-174.9 kJ/mol)
D)(+174.9 kJ/mol)
E)(+244.2 kJ/mol)

Question 62

Hydrogen reacts with nitrogen to form ammonia (NH₃) according to the reaction

The value of $\Delta$ H ^$\circ$ is -92.38 kJ/mol, and that of $\Delta$ S ^$\circ$ is -198.2 J/(mol . K). Determine $\Delta$ G ^$\circ$ at 25 ^$\circ$ C.

A)(-5.897 $\times$ 10⁴ kJ/mol)
B)(-297.8 kJ/mol)
C)(-33.32 kJ/mol)
D)(-16.66 kJ/mol)
E)(+49.5 kJ/mol)

Question 63

Alcohols for use as biofuels can be produced from glucose that is obtained from starch and cellulose in plants. Use the information in the table below to determine the free-energy change and whether or not this reaction is spontaneous at 78 ^$\circ$ C, which is the boiling point of an ethanol-water azeotrope.

A)(-6 kJ, spontaneous)
B)(+76 kJ, not spontaneous)
C)(-76 kJ, spontaneous)
D)(-258 kJ, not spontaneous)
E)(-258 kJ, spontaneous)

Question 64

Consider substances that exist as liquids under standard state conditions. What must be the relationship between the enthalpy and free energy of formation for the liquid and the gaseous form of such a substance? (Read < as more negative and > as less negative.)

A) (l ) < (g) and (l ) < (g)
B) (l ) < (g) and (l ) > (g)
C) (l ) > (g) and (l ) > (g)
D) (l ) > (g) and (l ) < (g)
E)No strict relationship between these values applies.

Question 65

Which of the following is/are true for a reversible process at equilibrium?
I. $\Delta$ S_univ = 0
II. $\Delta$ S_sys = 0
III. $\Delta$ 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 66

Determine given the following information:

A)(-2,705 kJ)
B)(-608.0 kJ)
C)(-1,791 kJ)
D)(-3,457 kJ)
E)(+608.0 kJ)

Question 67

The symbol $\Delta$ (MgSO₄, s) refers to which of the following reactions?

A)
B)
C)
D)
E)

Question 68

Hydrochloric acid (HCl) reacts with sodium hydroxide (NaOH) to form sodium chloride (NaCl) and water. If $\Delta$ H ^$\circ$ -56.13 kJ/mol and $\Delta$ S ^$\circ$ = 79.11 J/mol . K, what is the temperature of the reaction if $\Delta$ G ^$\circ$ = -80.89 kJ/mol?

A)154 ^$\circ$ C
B)313 ^$\circ$ C
C)0.313 ^$\circ$ C
D)40.0 ^$\circ$ C
E)75 ^$\circ$ C

Question 69

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

A)( $\Delta$ H > 0 and $\Delta$ S < 0)
B)( $\Delta$ H < 0 and $\Delta$ S < 0)
C)( $\Delta$ H > 0 and $\Delta$ S > 0)
D)( $\Delta$ H < 0 and $\Delta$ S > 0)
E)None of these is true, because temperature must always be taken into account.

Question 70

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

A)(-79.31 kJ/mol)
B)(-77.73 kJ/mol)
C)(-2.324 $\times$ 10⁴ kJ/mol)
D)79.31 kJ/mol
E)(-1,638 kJ/mol)

Question 71

Determine the value of $\Delta$ G ^$\circ$ for the reaction at 298 K.
Given

A)(-88.8 kJ)
B)(+88.8 kJ)
C)(+192 kJ)
D)(-192 kJ)
E)(-3.38 kJ)

Question 72

Determine the value of $\Delta$ G ^$\circ$ for the reaction at 298 K. Given

A)(-962 kJ)
B)(+573 kJ)
C)(-573 kJ)
D)(-817 kJ)
E)(+817 kJ)

Question 73

Determine the value of $\Delta$ G ^$\circ$ for the reaction given

A)(-4.8 kJ)
B)(+4.8 kJ)
C)(+52.3 kJ)
D)(-52.3 kJ)
E)(-43 kJ)

Question 74

What is the maximum amount of work that can be done by the reaction

A)(-50.8 kJ/mol)
B)(-751 kJ/mol)
C)(+113 kJ/mol)
D)(-115 kJ/mol)
E)(-807 kJ/mol)

Question 75

The reaction where en represents ethylenediamine, has a small value for the enthalpy change, $\Delta$ H_rxn, yet the free-energy change is large because ________

A)the reaction rate is fast.
B)the entropy change is large and positive.
C)the enthalpy change is large enough to matter.
D)the entropy change is large and negative.
E)ethylenediamine has amino groups that are stronger bases than ammonia.

Question 76

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

A)( $\Delta$ S_rxn = 0.)
B)( $\Delta$ = 0.)
C)( $\Delta$ G_rxn = 0.)
D)( = 0.)
E)( $\Delta$ H_rxn = 0.)

Question 77

The symbol $\Delta$ (NH₄NO₃, s) refers to which of the following reactions?

A)
B)
C)
D)
E)

Question 78

Given the following data, determine the molar free energy of combustion for propane gas, C₃H₈. (C₃H₈, g) -23.5 kJ/mol (CO₂, g) -394.4 kJ/mol (H₂O, g) -5.6 kJ/mol

A)(-1,629.1 kJ/mol)
B)(-1,582.1 kJ/mol)
C)(-476.5 kJ/mol)
D)(+476.5 kJ/mol)
E)(+1,582.1 kJ/mol)

Question 79

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

A)( $\Delta$ G = 0 and $\Delta$ G ^$\circ$ = 0.)
B)( $\Delta$ G = 0 and $\Delta$ G ^$\circ$ > 0.).
C)( $\Delta$ G = 0 and $\Delta$ G ^$\circ$ < 0.)
D)( $\Delta$ G = 0 and $\Delta$ G ^$\circ$ = 0.) .
E)( $\Delta$ G < 0 and $\Delta$ G ^$\circ$ = 0.)

Question 80

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

A)( $\Delta$ G_sys > 0.)
B)( $\Delta$ G_sys < 0.)
C)( $\Delta$ S_sys > 0.)
D)( $\Delta$ S_sys < 0.)
E)( $\Delta$ H_sys < 0.)