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

Question 1

A certain process has $\Delta$ S_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 is correct.

Answer 1

It is spontaneous at 25°C.

Question 2

Which relationship or statement best describes $\Delta$ S° for the following reaction?
C₂H₅OH(l)+ 3O₂(g) $\to$ 2CO₂(g)+ 3H₂O(l)

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

Answer 2

( $\Delta$ S° < 0)

Question 3

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

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

Answer 3

N₂(g),25°C $\to$ N₂(aq),25°C

Question 4

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 5

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

A)( $\Delta$ S° $\approx$ 00
B)9 $\Delta$ S° < 0)
C)( $\Delta$ S° > 0)
D)( $\Delta$ S° = $\Delta$ H°/T)
E)More information is needed to make a reasonable prediction.

Question 6

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

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

Question 7

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

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

Question 8

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

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

Question 9

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 because he had planned the jump for two weeks.
D)spontaneous.
E)in equilibrium.

Question 10

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 11

Which relationship or statement best describes $\Delta$ S° for the following reaction?
O₃(g)+ NO(g) $\to$ O₂(g)+ NO₂(g)

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

Question 12

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

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

Question 13

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

A)9 $\Delta$ S° = $\Delta$ H°)
B)( $\Delta$ S° = $\Delta$ H°/T)
C)( $\Delta$ S° $\approx$ )
D)( $\Delta$ S° < 0)
E)( $\Delta$ S° > 0)

Question 14

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 15

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

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

Question 16

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 17

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

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

Question 18

Which relationship or statement best describes $\Delta$ S° for the following reaction?
K₂SO₄(s) $\to$ 2K⁺(aq)+ SO₄^2-(aq)

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

Question 19

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

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

Question 20

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

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

Question 21

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

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

Question 22

Elemental boron can be formed by reaction of boron trichloride with hydrogen.
BCl₃(g)+ 1.5H₂(g) $\to$ B(s)+ 3HCl(g)

If $\Delta$ S° = 80.3 J/K,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 23

Calculate $\Delta$ S° for the reaction
2Cl₂(g)+ SO₂(g) $\to$ 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 24

Calculate $\Delta$ S° for the combustion of propane.
C₃H₈(g)+ 5O₂(g) $\to$ 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 25

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°C;1 mole of H₂(g)at 50°C
E)1 mole of O₃(g);1 mole of O₂(g)

Question 26

Calculate $\Delta$ S° for the reaction
SiCl₄(g)+ 2Mg(s) $\to$ 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 27

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 28

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 $\approx$ (S°_toluene) $\div$ 3
D)S°_ethane $\approx$ S°_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 29

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 30

Which relationship or statement best describes $\Delta$ S° for the following reaction?
CaO(s)+ CO₂(g) $\to$ CaCO₃(s)

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

Question 31

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 32

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 $\approx$ 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 33

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

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

Question 34

Which of the following pairs has the member with the greater molar entropy listed first? All systems are at 25°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 35

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

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

Question 36

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

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

Question 37

Which relationship or statement best describes $\Delta$ S° for the following reaction?
BaCl₂(aq)+ Na₂SO₄(aq) $\to$ BaSO₄(s)+ 2NaCl(aq)

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

Question 38

Calculate $\Delta$ S° for the reaction
4Cr(s)+ 3O₂(g) $\to$ 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 39

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

A)S°(pentane)> S°(1,3-pentadiene)
B)S°(pentane)< S°(1,3-pentadiene)
C)S°(pentane) $\approx$ S°(1,3-pentadiene)
D)S°(pentane)= S°(1,3-pentadiene)+ 2 $\times$ S°(H₂)
E)More information is needed to make reasonable predictions.

Question 40

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 41

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

A)( $\Delta$ H° > 0, $\Delta$ S° > 0)
B)( $\Delta$ H° > 0, $\Delta$ S° < 0)
C)9 $\Delta$ H° < 0, $\Delta$ S° > 0)
D)( $\Delta$ H° < 0, $\Delta$ S° < 0)
E)None of these choices is correct.

Question 42

Sulfuryl dichloride is formed when sulfur dioxide reacts with chlorine.The data refer to 298 K.
SO₂(g)+ Cl₂(g) $\to$ SO₂Cl₂(g)

What is the value of $\Delta$ G° 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 43

Consider the figure below which shows $\Delta$ G° 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)( $\Delta$ H° > 0)
B)( $\Delta$ S° > 0)
C)The reaction is spontaneous at high temperatures.
D)( $\Delta$ S° increases with temperature while $\Delta$ H° remains constant.)
E)(There exists a certain temperature at which $\Delta$ H° = T $\Delta$ S°.)

Question 44

Nitric oxide reacts with chlorine to form NOCl.The data refer to 298 K.
2NO(g)+ Cl₂(g) $\to$ 2NOCl(g)

What is the value of $\Delta$ G° for this reaction at 550 K?

A)-143.76 kJ
B)-78.78 kJ
C)-22.24 kJ
D)-10.56 kJ
E)66,600 kJ

Question 45

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 $\times$ 10¹⁹
B)0.96
C)0.58
D)1.2 $\times$ 10^-20
E)1.4 $\times$ 10^-46

Question 46

What is the free energy change, ^$\circ$ G°,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 47

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.
CH₄(g)+ 2H₂O(g)
CO₂(g)+ 4H₂(g)

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

Question 48

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 $\times$ 10^-6
B)1.3 $\times$ 10^-3
C)2.2 $\times$ 10⁴
D)1.4 $\times$ 10⁵
E) > 2.0 $\times$ 10⁵

Question 49

a.Explain what is meant by a spontaneous process.
b.Is a spontaneous process necessarily a rapid one? Explain,and provide a real reaction as an example to illustrate your answer.

Question 50

Use the given data at 298 K to calculate $\Delta$ G° for the reaction
2Cl₂(g)+ SO₂(g) $\to$ 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 51

Calculate $\Delta$ G° for the reaction of ammonia with fluorine.
2NH₃(g)+ 5F₂(g) $\to$ 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 is correct.

Question 52

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 $\times$ 10⁸
C)1.59 $\times$ 10^-9
D)5.47 $\times$ 10^-21
E)2.18 $\times$ 10^-27

Question 53

Calculate $\Delta$ G° for the reaction
SiCl₄(g)+ 2Mg(s) $\to$ 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 54

Hydrogen sulfide decomposes according to the following reaction
2H₂S(g) $\to$ 2H₂(g)+ S₂(g)
For this reaction at 298K $\Delta$ S° = 78.1 J/K, $\Delta$ H° = 169.4 kJ,and $\Delta$ G° = 146.1 kJ.What is the value of $\Delta$ G° at 900 K?

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

Question 55

Calculate $\Delta$ G° for the combustion of propane.
C₃H₈(g)+ 5O₂(g) $\to$ 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 56

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 data at 298 K to determine this temperature.

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

Question 57

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 58

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

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

Question 59

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

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

Question 60

Elemental boron can be formed by reaction of boron trichloride with hydrogen.
BCl₃(g)+ 1.5H₂(g) $\to$ B(s)+ 3HCl(g)
Calculate $\Delta$ G° 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 61

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

Question 62

Given: C₂H₂(g) $\to$ 2C(graphite)+ H₂(g) $\Delta$ G° = -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° and the apparent stability of the sample.

Question 63

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

Question 64

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

Question 65

The water-gas shift reaction plays an important role in the production of clean fuel from coal.
CO(g)+ H₂O(g)
CO₂(g)+ H₂(g)
Use the following thermodynamic data to determine the equilibrium constant K_p at 700.K.

Question 66

For the reaction of xenon and fluorine gases to form solid XeF₄, $\Delta$ H° = -251 kJ and $\Delta$ G° = -121 kJ at 25°C.Calculate $\Delta$ S° for the reaction.

Question 67

Compare one mole of ice with one mole of liquid water,both at 1.0 atm and 0°C.The melting point of ice at 1.0 atm is 0°C.For the process
H₂O(s) $\to$ H₂O(l)
under these conditions predict whether each of the following quantities will be greater than,less than,or equal to,zero .Explain each prediction in one sentence.
a. $\Delta$ H°
b. $\Delta$ S°
c. $\Delta$ G°

Question 68

For what signs of $\Delta$ H and $\Delta$ S will a process
a.be spontaneous at high temperatures but not at low temperatures?
b.not be spontaneous at any temperatures?

Question 69

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

Question 70

For each of the following pairs,predict which (A or B)will have the greater entropy,and in one sentence indicate your reasoning.

Question 71

State the second and third laws of thermodynamics.

Question 72

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

Question 73

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 74

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

Question 75

A chemical reaction has $\Delta$ G° = 10.0 kJ and $\Delta$ S° = 50.0 J/K
a.Calculate $\Delta$ H° for this reaction at 25°C.
b.Could this reaction ever be spontaneous? Explain your answer.

Question 76

For a reaction at equilibrium, $\Delta$ S_univ = 0.

Question 77

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

Question 78

The complete combustion of liquid benzene is represented by the equation:
C₆H₆(l)+ 7
O₂(g) $\to$ 6CO₂(g)+ 3H₂O(l)
Using the data below,calculate,for this reaction
a. $\Delta$ H°
b. $\Delta$ S°
c. $\Delta$ G° at 25°C.

Question 79

Photosynthesis can be represented by the equation
6CO₂(g)+ 6H₂O(l) $\to$ C₆H₁₂O₆(s)+ 6O₂(g)
a.Calculate $\Delta$ S° for this process,given the following data:

b.Given that $\Delta$ H° for the reaction is 2802 kJ,calculate $\Delta$ G° at 25°C.

Question 80

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