Deck 20: Thermodynamics: Entropy, Free Energy, and the Direction of Chemical Reactions

Question 1

Which relationship or statement best describes $\Delta$ S $\degree$ for the following reaction?
Pb(s) + Cl₂(g) $\rightarrow$ PbCl₂(s)

A) ( $\Delta$ S $\degree$ $\approx$ 0)
B)( $\Delta$ S $\degree$ < 0)
C) ( $\Delta$ S $\degree$ > 0)
D)( $\Delta$ S $\degree$ = $\Delta$ H $\degree$ /T)
E) More information is needed to make a reasonable prediction.

Answer 1

( $\Delta$ S $\degree$ < 0)

Question 2

Which relationship or statement best describes $\Delta$ S $\degree$ for the following reaction?

A) ( $\Delta$ S $\degree$$\approx$ 0
B) ( $\Delta$ S $\degree$ < 0)
C)( $\Delta$ S $\degree$ > 0)
D)( $\Delta$ S $\degree$ = $\Delta$ H $\degree$ /T)
E) More information is needed to make a reasonable prediction.

Answer 2

( $\Delta$ S $\degree$ < 0)

Question 3

Which relationship or statement best describes $\Delta$ S $\degree$ for the following reaction?

A) ( $\Delta$ S $\degree$ $\approx$ 0)
B) ( $\Delta$ S $\degree$ < 0)
C) ( $\Delta$ S $\degree$ > 0)
D) ( $\Delta$ S $\degree$ = $\Delta$ H $\degree$ /T)
E) More information is needed to make a reasonable prediction.

Answer 3

( $\Delta$ S $\degree$ > 0)

Question 4

Which relationship or statement best describes $\Delta$ S $\degree$ for the following reaction? 2NH₃(g) + 2ClF₃(g) $\rightarrow$ 6HF(g) + N₂(g) + Cl₂(g)

A) ( $\Delta$ SF $\degree$$\approx$ 0)
B) ( $\Delta$ S $\degree$ < 0)
C) ( $\Delta$ S $\degree$ > 0)
D) ( $\Delta$ S $\degree$ = $\Delta$ H $\degree$ /T)
E) More information is needed to make a reasonable prediction.

Question 5

Which relationship best describes $\Delta$ S $\degree$ for the following reaction?
CO(g) + H₂O(g) $\rightarrow$ CO₂(g) + H₂(g)

A) ( $\Delta$ S $\degree$ = $\Delta$ H $\degree$ )
B) ( $\Delta$ S $\degree$ = $\Delta$ H $\degree$ T)
C) ( $\Delta$ S $\degree$ > 0)
D) ( $\Delta$ S $\degree$ < 0)
E) ( $\Delta$ S $\degree$$\approx$ 0)

Question 6

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 7

Which relationship best describes $\Delta$ S $\degree$ for the following reaction?
8H₂(g) + S₈(s) $\rightarrow$ 8H₂S(g)

A) ( $\Delta$ S $\degree$ = $\Delta$ H $\degree$ )
B) ( $\Delta$ S $\degree$ = $\Delta$ H $\degree$ /T)
C) ( $\Delta$ S $\degree$ $\approx$ 0)
D) ( $\Delta$ S $\degree$ < 0)
E) ( $\Delta$ S $\degree$ > 0)

Question 8

A certain process has $\Delta$ S_univ > 0 at 25 $\degree$ C. What does one know about the process?

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

Question 9

Which relationship or statement best describes $\Delta$ S $\degree$ for the following reaction?

A) ( $\Delta$ S $\degree$$\approx$ 0)
B)( $\Delta$ S $\degree$ < 0)
C) ( $\Delta$ S $\degree$ > 0)
D)( $\Delta$ S $\degree$ = $\Delta$ H $\degree$ /T)
E) More information is needed to make a reasonable prediction.

Question 10

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

A) O₂(g), 300 K $\rightarrow$ O₂(g), 400 K
B) H₂O(s), 0 $\degree$ C $\rightarrow$ H₂O(l), 0 $\degree$ C
C) N₂(g), 25 $\degree$ C $\rightarrow$ N₂(aq), 25 $\degree$ C
D) NH₃(l), -34.5 $\degree$ C $\rightarrow$ NH₃(g), -34.5 $\degree$ C
E) 2H₂O₂(g) $\rightarrow$ 2H₂O(g) + O₂(g)

Question 11

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

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

Question 12

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

A) CH₄(g)
B) H₂O(l)
C) NaCl(s)
D) N₂O₄(g)
E) H₂(g)

Question 13

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

A) q_sys > 0, $\Delta$ S_surr < 0
B) q_sys < 0, $\Delta$ S_surr > 0
C) q_sys < 0, $\Delta$ S_surr < 0
D) q_sys > 0, $\Delta$ S_surr > 0
E) w < 0

Question 14

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

A) ( $\Delta$ S $\degree$ _sys = $\Delta$ S $\degree$ _surr)
B) ( $\Delta$ S $\degree$ _sys = - $\Delta$ S $\degree$ _surr)
C) ( $\Delta$ S $\degree$ _sys = $\Delta$ S $\degree$ _surr = 0
D) ( $\Delta$ S $\degree$ _univ > 0)
E) None of these choices is a sufficient condition.

Question 15

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

A) q_sys > 0, $\Delta$ S_surr < 0
B) q_sys < 0, $\Delta$ S_surr > 0
C) q_sys < 0, $\Delta$ S_surr < 0
D) q_sys > 0, $\Delta$ S_surr > 0
E) w < 0

Question 16

Which relationship or statement best describes $\Delta$ S $\degree$ for the following reaction? HgS(s) + O₂(g) $\rightarrow$ Hg(l) + SO₂(g)

A)( $\Delta$ S $\degree$$\approx$ 0)
B) ( $\Delta$ S $\degree$ < 0)
C) ( $\Delta$ S $\degree$ > 0)
D) ( $\Delta$ S $\degree$ = $\Delta$ H $\degree$ /T)
E) More information is needed to make a reasonable prediction.

Question 17

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

A) H₂O(l) $\rightarrow$ H₂O(s) at 25 $\degree$ C
B) CO₂(s) $\rightarrow$ CO₂(g) at 0 $\degree$ C
C) 2H₂O(g) $\rightarrow$ H₂(g) + O₂(g)
D) C(graphite) $\rightarrow$ C(diamond) at 25 $\degree$ C and 1 atm pressure
E) None of these choices is spontaneous.

Question 18

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

A) ( $\Delta$ H $\degree$ _f > 0)
B) ( $\Delta$ H $\degree$ _f < 0)
C) ( $\Delta$ G $\degree$ _f > 0)
D) ( $\Delta$ G $\degree$ _f < 0)
E) (S $\degree$ > 0)

Question 19

Which relationship or statement best describes $\Delta$ S $\degree$ for the following reaction? 2H₂S(g) + 3O₂(g) $\rightarrow$ 2H₂O(g) + 2SO₂(g)

A) ( $\Delta$ S $\degree$$\approx$ 0)
B) ( $\Delta$ S $\degree$ < 0)
C) ( $\Delta$ S $\degree$ > 0)
D) ( $\Delta$ S $\degree$ = $\Delta$ H $\degree$ /T)
E) More information is needed to make a reasonable prediction.

Question 20

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

A) ( $\Delta$ H $\degree$ _f = 0 for Al(s) at 298 K)
B)( $\Delta$ G $\degree$ _f = 0 for H₂(g) at 298 K)
C) (S $\degree$ = 51.446 J/(mol·K) for Na(s) at 298 K)
D) (q _sys < 0 for H₂O(l) $\rightarrow$ H₂O(s) at 0 $\degree$ C)
E) None of these choices is correct.

Question 21

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

A) ( $\Delta$ S $\degree$ > 0, $\Delta$ H $\degree$ > 0)
B) ( $\Delta$ S $\degree$ > 0, $\Delta$ H $\degree$ < 0)
C) ( $\Delta$ S $\degree$ < 0, $\Delta$ H $\degree$ < 0)
D) ( $\Delta$ S $\degree$ < 0, $\Delta$ H $\degree$ > 0)
E) It is not possible for a reaction to be spontaneous at all temperatures.

Question 22

You are given pure samples of pentane, $\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{CH}_{2} \mathrm{CH}_{2} \mathrm{CH}_{3}(l)$ , and 1,3-pentadiene, $\mathrm{CH}_{2}=\mathrm{CHCH}=\mathrm{CHCH}_{3}(l)$ What prediction would you make concerning their standard molar entropies at 298 K?

A) S $\degree$ _pentane > S $\degree$ _{1,3-pentadiene}
B) S $\degree$ _pentane < S $\degree$ _{1,3-pentadiene}
C) S $\degree$ _pentane $\approx$ S $\degree$ _{1,3-pentadiene}
D) S $\degree$ _pentane  S $\degree$ _{1,3-pentadiene} + 2*
E) More information is needed to make reasonable predictions.

Question 23

Calculate $\Delta$ S $\degree$ for the reaction

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 24

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 O₂(g); 2 mole O(g)
C) 1 mole CH₄(g); 1 mole C₂H₆(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 25

Which relationship or statement best describes $\Delta$ S $\degree$ for the following reaction?

A) ( $\Delta$ S $\degree$ F $\approx$ 0)
B) ( $\Delta$ S $\degree$ < 0)
C)( $\Delta$ S $\degree$ > 0)
D)( $\Delta$ S $\degree$ = $\Delta$ H $\degree$ /T)
E) More information is needed to make a reasonable prediction.

Question 26

Calculate $\Delta$ S $\degree$ for the reaction

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 27

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 28

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 5 K 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 29

Elemental boron can be formed by reaction of boron trichloride with hydrogen. If $\Delta$ S $\degree$ = 80.3 J/K for the reaction above, what is S $\degree$ 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 30

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

A) ( $\Delta$ S $\degree$ > 0, $\Delta$ H $\degree$ > 0)
B) ( $\Delta$ S $\degree$ > 0, $\Delta$ H $\degree$ < 0)
C) ( $\Delta$ S $\degree$ < 0, $\Delta$ H $\degree$ < 0)
D) ( $\Delta$ S $\degree$ < 0, $\Delta$ H $\degree$ > 0)
E) ( $\Delta$ G $\degree$ > 0)

Question 31

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 $\degree$ _ammonia > S $\degree$ _{nitrogen trifluoride}
B) S $\degree$ _ammonia < S $\degree$ _{nitrogen trifluoride}
C) S $\degree$ _ammonia $\approx$ S $\degree$ _{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 32

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

A) ( $\Delta$ S $\degree$ > 0, $\Delta$ H $\degree$ > 0)
B) ( $\Delta$ S $\degree$ > 0, $\Delta$ H $\degree$ < 0)
C) ( $\Delta$ S $\degree$ < 0, $\Delta$ H $\degree$ < 0)
D) ( $\Delta$ S $\degree$ < 0, $\Delta$ H $\degree$ > 0)
E) All reactions are spontaneous at some temperature.

Question 33

Which relationship or statement best describes $\Delta$ S $\degree$ for the following reaction?

A) ( $\Delta$ S $\degree$$\approx$ 0)
B) ( $\Delta$ S $\degree$ < 0)
C)( $\Delta$ S $\degree$ > 0)
D) ( $\Delta$ S $\degree$ = $\Delta$ H $\degree$ /T)
E) More information is needed to make a reasonable prediction.

Question 34

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

A)( $\Delta$ S $\degree$ > 0, $\Delta$ H $\degree$ > 0)
B) ( $\Delta$ S $\degree$ > 0, $\Delta$ H $\degree$ < 0)
C) ( $\Delta$ S $\degree$ < 0, $\Delta$ H $\degree$ < 0)
D) ( $\Delta$ S $\degree$ < 0, $\Delta$ H $\degree$ > 0)
E) ( $\Delta$ G $\degree$ > 0)

Question 35

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 F₂(g); 1 mole of Cl₂(g)
B) 1 mole of I₂(s); 1 mole of I₂(g)
C) 1 mole of CaCO₃(s); 1 mole of CaO(s) plus 1 mole of CO₂(g)
D) 1 mole of H₂(g) at 25 $\degree$ C; 1 mole of H₂(g) at 50 $\degree$ C
E) 1 mole of O₃(g); 1 mole of O₂(g)

Question 36

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 37

Calculate $\Delta$ S $\degree$ for the reaction

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 38

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 $\degree$ _ethane > S $\degree$ _toluene
B) S $\degree$ _ethane < S $\degree$ _toluene
C) S $\degree$ _ethane $\approx$ (S $\degree$ _toluene) / 3
D) S $\degree$ _ethane $\approx$ S $\degree$ _toluene
E) Since toluene is much more complex than ethane, but ethane is in the gas phase while toluene is a liquid, none of these predictions can be confidently made without further information or calculations.

Question 39

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

A) CO(g), CO₂(g)
B) NaCl(s), NaCl(aq)
C) H₂S(g), H₂S(aq)
D) Li(s), Pb(s)
E) H₂(g), H₂O(g)

Question 40

Calculate $\Delta$ S $\degree$ for the combustion of propane.

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 41

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

A) ( $\Delta$ H > 0)
B) ( $\Delta$ H < 0)
C) ( $\Delta$ S_sys > 0)
D) ( $\Delta$ S_surr > $\Delta$ S_sys)
E) ( $\Delta$ S > $\Delta$ H/T)

Question 42

Calculate $\Delta$ G $\degree$ for the combustion of propane.

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

Question 43

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 towards a state of lower entropy.
D) the universe proceeds towards a state of higher entropy.
E) the universe cannot create entropy.

Question 44

Consider the figure below which shows $\Delta$ G $\degree$ for a chemical process plotted against absolute temperature. From this plot, it is reasonable to conclude that:

A) ( $\Delta$ H $\degree$ > 0, $\Delta$ S $\degree$ > 0)
B)( $\Delta$ H $\degree$ > 0, $\Delta$ S $\degree$ < 0)
C)( $\Delta$ H $\degree$ < 0, $\Delta$ S $\degree$ > 0)
D)( $\Delta$ H $\degree$ < 0, $\Delta$ S $\degree$ < 0)
E) None of these choices is correct.

Question 45

Consider the figure below which shows $\Delta$ G $\degree$ for a chemical process plotted against absolute temperature. From this plot, it is reasonable to conclude that:

A)( $\Delta$ H $\degree$ > 0, $\Delta$ S $\degree$ > 0)
B) ( $\Delta$ H $\degree$ > 0, $\Delta$ S $\degree$ < 0)
C) ( $\Delta$ H $\degree$ < 0, $\Delta$ S $\degree$ > 0)
D) ( $\Delta$ H $\degree$ < 0, $\Delta$ S $\degree$ < 0)
E) None of these choices is correct.

Question 46

"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 298 K and determine whether or not a diamond is "forever." C(diamond) $\degree$ C(graphite)
Data: $\Delta$ H_f $\degree$ (diamond) = 1.895 kJ/mol; S $\degree$ (diamond) = 2.337 J mol¯¹ K¯¹; S $\degree$ (graphite) = 5.740 J mol¯¹K¯¹.

A) ( $\Delta$ G $\degree$ = 2.19 kJ; forever
B) ( $\Delta$ G $\degree$ = -1.90 kJ; not forever)
C) ( $\Delta$ G $\degree$ = -2.90 kJ; not forever)
D)( $\Delta$ G $\degree$ = 1.90 kJ; forever)
E) ( $\Delta$ G $\degree$ = < -1000 kJ; not forever)

Question 47

Sulfuryl dichloride is formed when sulfur dioxide reacts with chlorine. The data refer to 298 K. What is the value of $\Delta$ G $\degree$ 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 48

Use the given data at 298 K to calculate $\Delta$ G $\degree$ for the reaction

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

Question 49

Given: H₂O(l) $\rightarrow$ H₂O(s), $\Delta$ H $\degree$ = -6.02 kJ at 273K, calculate the entropy change of the surroundings ( $\Delta$ S_surr) when one mole of water freezes at 0 $\degree$ 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 50

The temperature at which the following process reaches equilibrium at 1.0 atm is the normal boiling point of hydrogen peroxide.

Question 51

Calculate $\Delta$ G $\degree$ for the reaction

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

Question 52

Hydrogen sulfide decomposes according to the following reaction: For this reaction at 298 K, $\Delta$ S $\degree$ = 78.1 J/K, $\Delta$ H $\degree$ = 169.4 kJ, and $\Delta$ G $\degree$ = 146.1 kJ. What is the value of $\Delta$ G $\degree$ at 900 K?

A) -69,881 kJ
B) 48.4 kJ
C) 99.1 kJ
D) 240 kJ
E) 441 kJ

Question 53

For a process with $\Delta$ S < 0, which one of the following statements is correct?

A) The process will definitely be spontaneous if $\Delta$ H < 0.
B) The process will be definitely be spontaneous if $\Delta$ H < T $\Delta$ S.
C) The process can never be spontaneous.
D) The process will definitely be spontaneous, regardless of $\Delta$ H.
E) The process will definitely be spontaneous if $\Delta$ S_surr > 0.

Question 54

Given: H₂O(l) $\rightarrow$ H₂O(g), $\Delta$ H $\degree$ = 40.7 kJ at 373K, what is the entropy change in the system ( $\Delta$ S) when one mole of water vaporizes at 100 $\degree$ 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 55

Elemental boron can be formed by reaction of boron trichloride with hydrogen. Calculate $\Delta$ G $\degree$ for the reaction.

A) -293.4 kJ
B) 293.4 kJ
C) -102.8 kJ
D) 102.8 kJ
E) None of these choices is correct.

Question 56

A certain process has $\Delta$ 0H $\degree$ > 0, $\Delta$ S $\degree$ < 0, and $\Delta$ G $\degree$ > 0. The values of $\Delta$ H $\degree$ and $\Delta$ S $\degree$ 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 conclusions is correct.

Question 57

In order for a process to be spontaneous,

A) ( $\Delta$ H must be less than zero.)
B) ( $\Delta$ S must be greater than zero.)
C) ( $\Delta$ G must be greater than zero.)
D) it should be rapid.
E) ( $\Delta$ S_sys + $\Delta$ S_surr must be greater than zero.)

Question 58

Calculate $\Delta$ G $\degree$ for the reaction of ammonia with fluorine.

A) 179.1 kJ
B) -179.1 kJ
C) 1539.7 kJ
D) -1539.7 kJ
E) None of these choices is correct.

Question 59

Nitric oxide reacts with chlorine to form NOCl. The data refer to 298 K. What is the value of $\Delta$ G $\degree$ 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 60

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 61

The formation constant for the reaction Ag⁺(aq) + 2NH₃(aq) Ag(NH₃)₂⁺(aq) is K_f = 1.7 *10⁷ at 25 $\degree$ C. What is $\Delta$ G $\degree$ at this temperature?

A) -1.5 kJ
B) -3.5 kJ
C) -18 kJ
D) -23 kJ
E) -41 kJ

Question 62

In tables of thermodynamic data provided in chemistry books, one finds $\Delta$ H $\degree$ _f, $\Delta$ G $\degree$ _f and S $\degree$ listed. Briefly, explain why the entropy data are supplied as S $\degree$ , while the enthalpy and free energy data are in the form of $\Delta$ H $\degree$ _f and $\Delta$ G $\degree$ 1U1B1f, respectively.

Question 63

Given: C₂H₂(g) $\rightarrow$ 2C(graphite) + H₂(g), $\Delta$ G $\degree$ = -209 kJ
A sample of gaseous C₂H₂ (acetylene, or ethyne) was stored for one year, yet at the end of this period, the sample remained unchanged and no graphite or hydrogen gas had been formed. Briefly explain why there is no inconsistency between the sign of $\Delta$ G $\degree$ and the apparent stability of the sample.

Question 64

The water-gas shift reaction plays an important role in the production of clean fuel from coal.

Question 65

A reaction has a positive value of $\Delta$ H $\degree$ and a positive value of $\Delta$ S $\degree$ . Draw a neat, labeled schematic plot to show how $\Delta$ G $\degree$ (y-axis) will depend on absolute temperature (x-axis).

Question 66

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

Question 67

A reaction has $\Delta$ G= 10.0 kJ and $\Delta$ G $\degree$ = 15.0 kJ at a temperature of 50 $\degree$ C. Calculate the value of the reaction quotient Q under these conditions.

A) 0.16
B) 9.1 * 10¯⁵
C) 1.1 *10⁴
D) 6.4
E) 6.0 * 10¯⁶

Question 68

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 * 10⁸
C) 1.59 * 10¯⁹
D) 5.47 * 10¯²¹
E) 2.18 * 10¯²⁷

Question 69

Iron(III) oxide can be reduced by carbon monoxide.

Question 70

The reaction of methane with water to form carbon dioxide and hydrogen is non-spontaneous at 298 K. At what temperature will this system make the transition from non-spontaneous to spontaneous? The data refer to 298 K.

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

Question 71

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 72

In the expression, S = k ln W, W is called the number of microstates. Explain clearly the meaning of the word "microstate," and why a system under a given set of conditions normally has many microstates.

Question 73

State the second and third laws of thermodynamics.

Question 74

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

Question 75

A chemical reaction has $\Delta$ H $\degree$ = 42.8 kJ and $\Delta$ S $\degree$ = 92.5 J/K, at 25 $\degree$ C. Calculate the temperature at which $\Delta$ G $\degree$ = 0. State any approximation involved in your calculation.

Question 76

Consider the reaction If the concentrations of the Cu⁺ and I¯ ions in equilibrium at 298 K are both equal to 1.03 *10¯⁶ M, what is the value of $\Delta$ G $\degree$ for the reaction?

A) -68 kJ
B) 68 kJ
C) -30. kJ
D) 30 kJ
E) 34 kJ

Question 77

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

Question 78

What is the free energy change, $\Delta$ G $\degree$ , for the equilibrium between hydrogen iodide, hydrogen, and iodine at 453 $\degree$ C?
K_c = 0.020

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

Question 79

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

Question 80

A reaction is proceeding towards equilibrium. At a certain stage, the concentrations of reactants and products are such that $\Delta$ G = $\Delta$ G $\degree$ . 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