Deck 19: Principles of Chemical Reactivity: Entropy and Free Energy

Question 1

The standard entropy for the formation of sulfur hexafluoride from the sulfur and fluorine is -348.7 J/K ⋅mol-rxn at 298.15 K.What is the standard molar entropy of sulfur hexafluoride for the reaction below? (Given: S°[S(s)] = 32.1 J/K ⋅mol and S°[F2(g)] = 202.8 J/K ⋅mol)

A) -988.6 J/K⋅mol
B) +291.8 J/K⋅mol
C) -291.8 J/K⋅mol
D) -113.2 J/K⋅mol
E) +113.8 J/K⋅mol

Answer 1

+291.8 J/K⋅mol

Question 2

In which of the following reactions is Δ_rS° expected to be positive?

A) 2C₂H₆(g)+ 7O₂(g)→ 4CO₂(g)+ 6H₂O(l)
B) Ga(l)→ Ga(s)
C) H₂O(l)+ 2SO₂(g)→ H₂SO₄(l)
D) CO₂(g)→ CO₂(s)
E) None of these

Answer 2

None of these

Question 3

What is the standard entropy change for the following reaction? 4 N₂(g)
+ 12 H₂(g)
→
8 NH₃(g) (J/mol⋅K)
191)5
130)6
192)3

A) -794.8 J/K⋅mol-rxn
B) 794.8 J/K⋅mol-rxn
C) 2948.8 J/K⋅mol-rxn
D) -2948.8 J/K⋅mol-rxn
E) -129.8 J/K⋅mol-rxn

Answer 3

-794.8 J/K⋅mol-rxn

Question 4

Which of the following is the third law of thermodynamics as defined by Ludwig Boltzmann?

A) A perfect crystal at 0 K has zero entropy.
B) In a spontaneous process,the entropy of the universe increases.
C) The total entropy of the universe is always increasing.
D) The total mass of the universe is constant.
E) Mass and energy are conserved in all chemical reactions.

Question 5

For a certain reversible process,q = 88.06 kJ at 29.4°C.Which of the following is the ΔS for the process?

A) 0.291 J/K
B) 291 J/K
C) 3.00 J/K
D) -0.291 J/K
E) 2590 J/K

Question 6

Which of the following is the second law of thermodynamics?

A) In a spontaneous process,the entropy of the universe increases.
B) There is no disorder in a perfect crystal at 0 K.
C) The total energy of the universe is always increasing.
D) The total energy of the universe is constant.
E) Mass and energy are conserved in all chemical reactions.

Question 7

Calculate the standard entropy change for the following reaction: 2 SO₂(g)+ O₂(g)→ 2 SO₃(g)
Given: S°[SO₂(g)] = 248.2 J/K⋅mol,S°[O₂(g)] = 205.1 J/K⋅mol,and S°[SO₃(g)] = 256.8 J/K⋅mol.

A) -196.5 J/K·mol-rxn
B) -94.0 J/K·mol-rxn
C) -187.9 J/K·mol-rxn
D) +187.9 J/K·mol-rxn
E) +196.5 J/K·mol-rxn

Question 8

Which of the following represents the change in entropy for a system going from 142 possible microstates to 830 possible microstates? (k = 1.381 × 10^-23 J/K)

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

Question 9

Which of the following compounds has the highest standard entropy per mole at 298 K?

A) H₂O(l)
B) CaCO₃(s)
C) CO(g)
D) SiO₂(s)
E) CH₃OH(l)

Question 10

If a chemical reaction occurs in a direction that has a positive change in entropy,then _____.

A) the change in enthalpy must be negative.
B) the reaction must be spontaneous.
C) the heat goes from the system into the surroundings.
D) the reaction must be exothermic.
E) the disorder of the system increases.

Question 11

Which of the following linear chain alcohols is likely to have the highest standard entropy in the liquid state?

A) CH₃OH
B) CH₃CH₂OH
C) CH₃CH₂CH₂OH
D) CH₃CH₂CH₂CH₂OH
E) CH₃CH₂CH₂CH₂CH₂OH

Question 12

Which of the following changes lead to a decrease in entropy?

A) Sugar dissolving in coffee
B) Diffusion of perfume throughout a room
C) Evaporation of gasoline
D) The sublimation (vaporization)of dry ice (solid carbon dioxide)
E) Condensation of steam on glass

Question 13

Which of the following is true of the deposition of a gaseous substance?

A) ΔS° = 0 and ΔH° = 0.
B) ΔS° > 0 and ΔH° > 0.
C) ΔS° < 0 and ΔH° > 0.
D) ΔS° < 0 and ΔH° < 0.
E) ΔS° > 0 and ΔH° < 0.

Question 14

For which of the following reactions will the entropy of a system decrease?

A) 2 NH₃(g)→ N₂(g)+ 3 H₂(g)
B) 2 C(s)+ O₂(g)→ 2 CO(g)
C) CaCO₃(s)→ CaO(s)+ CO₂(g)
D) 2 NO₂(g)→ N₂O₄(g)
E) NaOH(s)→ Na⁺(aq)+ OH^-(aq)

Question 15

What is the S0 for ozone if the standard entropy change for the reaction below is 411 J/K⋅mol-rxn and S⁰[O₂(g)] = 205 J/K⋅mol. 6 O₃(g)→ 9 O₂(g)

A) 364 J/K⋅mol-rxn
B) 478 J/K⋅mol-rxn
C) 239 J/K⋅mol-rxn
D) −117 J/K⋅mol-rxn
E) −59 J/K⋅mol-rxn

Question 16

For the reaction Br₂(l)→ 2Br(g),_____.

A) ΔH is + and ΔS is +
B) ΔH is + and ΔS = 0
C) ΔH is - and ΔS is -
D) ΔH is - and ΔS is +
E) ΔH is + and ΔS is -

Question 17

Which of the following statements concerning entropy is not correct?

A) The entropy of a system increases as the number of available microstates increases.
B) The entropy of a system is proportional to the natural log of the number of microstates.
C) In a spontaneous process,ΔS(universe)indicates the extent to which energy is dispersed.
D) The dispersal of matter,such as the spontaneous expansion of a gas,cannot be explained by an increase in entropy.
E) Entropy is a measure of the extent of energy dispersal.

Question 18

Which of the following is the first law of thermodynamics?

A) In a spontaneous process,the entropy of the universe increases.
B) There is no disorder in a perfect crystal at 0 K.
C) The total energy of the universe is always decreasing.
D) Energy cannot be created or destroyed.
E) mass and energy are conserved in all chemical reactions.

Question 19

What is the sign of ΔH (system)and ΔS (system)if a chemical reaction is spontaneous only at lower temperatures under standard conditions?

A) ΔH (system)is negative,and ΔS (system)is negative.
B) ΔH (system)is positive,and ΔS (system)is positive.
C) ΔH (system)is positive,and ΔS (system)is negative.
D) ΔH (system)is negative,and ΔS (system)is positive.
E) None of these

Question 20

Calculate ΔS°(universe)for the combustion of acetylene at 298.15 K using the reaction below.(Given: ΔS°(system)= -194.6 J/K and ΔH°(system)= -2511.2 kJ) 2 C₂H₂(g)+ 5 O₂(g)→ 4 CO₂(g)+ 2 H₂O(g)

A) -2453.2 J/K
B) -186.2 J/K
C) +186.2 J/K
D) +1290.4 J/K
E) +8228.0 J/K

Question 21

A 100 mL sample of water is placed in a coffee cup calorimeter.When 1.0 g of an ionic solid is added,the temperature decreases from 21.5 °C to 20.8 °C as the solid dissolves.For the dissolving of the solid,_____.

A) ΔH < 0
B) ΔS(universe)> 0
C) ΔS(system)< 0
D) ΔS(surroundings)> 0
E) None of these

Question 22

While diluting concentrated sulfuric acid with water,the temperature of the solution increases rapidly.What are the signs of ΔrH,ΔrS,and ΔrG for the process?

A) Δ_rH < 0,Δ_rS > 0,and Δ_rG < 0
B) Δ_rH < 0,Δ_rS < 0,and Δ_rG < 0
C) Δ_rH < 0,Δ_rS > 0,and Δ_rG > 0
D) Δ_rH > 0,Δ_rS > 0,and Δ_rG < 0
E) Δ_rH > 0,Δ_rS < 0,and Δ_rG > 0

Question 23

For the reaction given below,ΔH⁰ = −1516 kJ at 25°C and ΔS⁰ = −432.8 J/K at 25°C.This reaction is spontaneous _____. SiH₄(g)+ 2 O₂(g)→ SiO₂(s)+ 2 H₂O

A) only below a certain temperature
B) only above a certain temperature
C) at all temperatures
D) only when entropy is zero
E) None of these

Question 24

At what temperatures will a reaction be spontaneous if Δ_rH° = +117 kJ and Δ_rS° = -35 J/K?

A) All temperatures below 94.1 K
B) Temperatures between 12.7 K and 135 K
C) All temperatures above 94.1 K
D) The reaction will be spontaneous at any temperature.
E) The reaction will never be spontaneous.

Question 25

If Δ_rG° > 0 for a reaction at all temperatures,then Δ_rH° is _____ and Δ_rS° is _____.

A) Negative; positive
B) Positive; negative
C) Negative; negative
D) Positive; positive
E) Positive; either positive or negative

Question 26

Calculate ΔG° at 298 K for the reaction below. I₂(g)+ Br₂(g)→ 2IBr(g)
Given: Δ_rH° = -11.6 kJ/mol-rxn; Δ_rS° = 12 J/K⋅mol-rxn at 298 K.

A) -8.02 kJ/mol-rxn
B) 15.2 kJ/mol-rxn
C) -15.2 kJ/mol-rxn
D) 3.59 × 10³ kJ/mol-rxn
E) -3.59 × 10³ kJ/mol-rxn

Question 27

A change of state occurring in a system is accompanied by 60.7 kJ of heat that is transferred to the surroundings at a constant pressure and at a constant temperature of 300 K.Calculate the ΔS(surroundings)for the process.

A) -202 J/K
B) -60.7 kJ/K
C) 202 J/K
D) 60.7 kJ/K
E) 239 kJ/K

Question 28

If a chemical reaction is exothermic but not spontaneous,which of the following must be true?

A) Δ_rG > 0,Δ_rS > 0,and Δ_rH > 0
B) Δ_rG < 0,Δ_rS > 0,and Δ_rH > 0
C) Δ_rG > 0,Δ_rS < 0,and Δ_rH > 0
D) Δ_rG < 0,Δ_rS < 0,and Δ_rH < 0
E) Δ_rG > 0,Δ_rS < 0,and Δ_rH < 0

Question 29

At what temperatures will a reaction be spontaneous if Δ_rH° = +62.4 kJ and Δ_rS° = +301 J/K?

A) All temperatures below 207 K
B) All temperatures above 207 K
C) Temperatures between 179 K and 235 K
D) The reaction will be spontaneous at any temperature
E) The reaction will never be spontaneous

Question 30

Calculate Δ_rG° at 25.0 °C for the reaction below. 2 Na(s)+ 2 H₂O( )→ 2 NaOH(aq)+ H₂(g)
Given: Δ_rH° = −366.6 kJ/mol-rxn and Δ_rS° = −154.2 J/K⋅mol-rxn.

A) -371.2 kJ/mol-rxn
B) -320.6 kJ/mol-rxn
C) -215.4 kJ/mol-rxn
D) +371.2 kJ/mol-rxn
E) +4634.9 kJ/mol-rxn

Question 31

ΔG° = 0 for a reaction indicates that _____.

A) the reaction favors formation of products
B) the reaction is at equilibrium
C) the reaction is nonspontaneous
D) the reaction is spontaneous
E) the reaction cannot reach equilibrium

Question 32

A flask containing helium gas is released into a closed room.Which of the following ideas concerning entropy is/are true?

A) ΔS(system)> 0
B) Matter is dispersed.
C) ΔS(universe)> 0
D) This process is spontaneous.
E) All of these statements are true.

Question 33

If a cube of ice at 0 °C is placed outside on a warm summer day,the ice will melt spontaneously.What are the signs of Δ_rH,Δ_rS,and Δ_rG for the process?

A) Δ_rH < 0,Δ_rS > 0,and Δ_rG < 0
B) Δ_rH < 0,Δ_rS < 0,and Δ_rG < 0
C) Δ_rH < 0,Δ_rS > 0,and Δ_rG > 0
D) Δ_rH > 0,Δ_rS > 0,and Δ_rG < 0
E) Δ_rH > 0,Δ_rS < 0,and Δ_rG > 0

Question 34

For a reaction,Δ_rH° = -208.8 kJ and Δ_rS° = -308.2 J/K.At what temperature will Δ_rG° = 0.00 kJ?

A) 0.68 K
B) 677.5 K
C) 1476 K
D) 6435 K
E) 0.85 K

Question 35

Hydrogen gas is prepared by electrolysis of water according to the reaction below. 2 H₂O( )→ 2 H₂(g)+ O₂(g)
Predict the signs of Δ_rH and Δ_rS.

A) Δ_rH > 0 and Δ_rS > 0
B) Δ_rH < 0 and Δ_rS > 0
C) Δ_rH > 0 and Δ_rS < 0
D) Δ_rH < 0 and Δ_rS < 0
E) Δ_rH = 0 and Δ_rS < 0

Question 36

For a chemical reaction,if Δ_rG° = 0,then _____.

A) K > 0
B) K = 0
C) K < 0
D) K > 1
E) K = 1

Question 37

Which of the following is correct for the condensation of gaseous oxygen at -188 °C? (The normal boiling point of oxygen is -183 °C.)

A) ΔH < 0,ΔS > 0,and ΔG > 0.
B) ΔH < 0,ΔS < 0,and ΔG >0.
C) ΔH > 0,ΔS < 0,and ΔG < 0.
D) ΔH = 0,ΔS = 0,and ΔG < 0.
E) ΔH > 0,ΔS > 0,and ΔG > 0.

Question 38

Which of the following is true of a reaction that is product-favored?

A) Q < K and _rG < 0
B) Q < K and _rG > 0
C) Q = K and _rG = 0
D) Q > K and _rG < 0
E) Q > K and _rG > 0

Question 39

When a real gas is compressed from low pressure to high pressure,its temperature increases.Which of the following is true for ΔH and ΔS?

A) ΔH < 0 and ΔS < 0
B) ΔH < 0 and ΔS > 0
C) ΔH > 0 and ΔS < 0
D) ΔH > 0 and ΔS > 0
E) ΔH < 0 and ΔS = 0

Question 40

The dissolution of ammonium nitrate occurs spontaneously in water at 25 °C.As ammonium nitrate dissolves,the temperature of the water decreases.What are the signs of Δ_rH,Δ_rS,and Δ_rG for this process?

A) Δ_rH > 0,Δ_rS < 0,and Δ_rG > 0
B) Δ_rH > 0,Δ_rS > 0,and Δ_rG > 0
C) Δ_rH > 0,Δ_rS > 0,and Δ_rG < 0
D) Δ_rH < 0,Δ_rS < 0,and Δ_rG < 0
E) Δ_rH < 0,Δ_rS > 0,and Δ_rG > 0

Question 41

_____ changes only occur in the direction that leads toward chemical equilibrium.

Question 42

Using the given data,determine ΔrG° at 500.0 K for the reaction below. Ba(s)+ H₂O(g)→ BaO(s)+ H₂(g)
Substance
Δ_fH°(kJ/mol-rxn)at 298 K
S° (J/K·mol-rxn)at 298 K
Ba(s)
0
62)8
H₂O(g)
-241.8
188)7
BaO(s)
-592
70)4
H₂(g)
0
130)6

A) 325.0 kJ/mol-rxn
B) -325.0 kJ/mol-rxn
C) 335.2 kJ/mol-rxn
D) -335.2 kJ/mol-rxn
E) -375.5 kJ/mol-rxn

Question 43

The standard free energy change for a chemical reaction is +13.3 kJ/mol.Which of the following is the equilibrium constant for the reaction at 125 °C? (R = 8.314 J/K⋅mol)

A) 2.8 × 10^-6
B) 2.0 × 10^-5
C) 4.7 × 10^-3
D) 1.8 × 10^-2
E) 2.1 × 10²

Question 44

Given the following data: S(g)+ O₂(g)→ SO₂(g)
Δ_rG° = -300.1 kJ/mol-rxn
2 S(g)+ 3 O₂(g)→ 2 SO₃(g)
Δ_rG° = -742.1 kJ/mol-rxn
Calculate Δ_fG° for the reaction below.
SO₂(g)+ 1/2 O₂(g)→ SO₃(g)

A) -1042.2 kJ/mol-rxn
B) -71.0 kJ/mol-rxn
C) +2.47 kJ/mol-rxn
D) +71.0 kJ/mol-rxn
E) +1042.2 kJ/mol-rxn

Question 45

For a chemical system,Δ_rG° and Δ_rG are equal when:

A) the system is in equilibrium.
B) the reactants and products are in standard state conditions.
C) the equilibrium constant,K,equals 0.
D) the reaction quotient,Q,is less than 1.
E) the reactants and products are in the gas phase.

Question 46

The standard free energy of formation of AgI(s)is -66.2 kJ/mol.Δ_rG° for the reaction 2AgI(s)→ 2Ag(s)+ I₂(s)is:

A) 132.4 kJ
B) 66.2 kJ
C) -132.4 kJ
D) -66.2 kJ
E) 800 KJ

Question 47

In any chemical process,energy must be conserved.This is the _____ law of thermodynamics.

Question 48

For which of the following substances is the standard free energy of formation not equal to zero at 298 K?

A) Xe(g)
B) Sn(s)
C) N₂(g)
D) Mg(g)
E) Mn(s)

Question 49

What is the equilibrium constant for the reaction below at 298 K? 2C(s)+ 3H₂(g)→ C₂H₆(g)
Given: Δ_rH° = -84.68 kJ; Δ_rS° = -173.8 J/K at 298 K.(R = 8.314 J/K⋅mol)

A) 5.8 × 10⁵
B) 1.0 × 10−5
C) 8.6 × 10^-10
D) 1.7 × 10^-6
E) 7.0 × 10¹⁴

Question 50

The standard free energy change associated with the dissolution of ammonium nitrate in water is -6.73 kJ/mol at 298.15 K. NH₄NO₃(s) NH₄NO₃(aq)
Which of the following is the equilibrium constant for the reaction? (R = 8.314 J/K⋅mol)

A) 1.9 × 10^-3
B) 6.6 × 10^-2
C) 1.0
D) 15
E) 5.2 × 10²

Question 51

What is the equilibrium constant for reaction below at 25 °C? (R = 8.314 J/K⋅mol) 2 NO(g)+ O₂(g) 2 NO₂(g); Δ_fG° [NO(g)] = +86.6 kJ/mol and Δ_fG° [NO₂(g)] = +51.2 kJ/mol.

A) 3.9 × 10^-13
B) 1.0 × 10-¹¹
C) 2.6 × 10¹²
D) 1.6 × 10⁶
E) 3.8 × 10²⁸

Question 52

The K_sp of silver bromide is 5.4 × 10−¹³ at 298 K. AgBr(s) Ag⁺(aq)+ Br−(aq)
What is Δ_rG°? (R = 8.314 J/K⋅mol)

A) −3.0 × 10¹ kJ/mol
B) −5.87 kJ/mol
C) 5.87 kJ/mol
D) 3.0 × 10¹ kJ/mol
E) 7.0 × 10¹ kJ/mol

Question 53

Thermodynamics can be used to determine all of the following except _____.

A) the temperature at which a reaction is spontaneous
B) the extent to which a reaction occurs
C) the direction in which a reaction is spontaneous
D) the rate of reaction
E) the entropy change of a reaction

Question 54

Using the given data,determine ΔrG° at 298 K for the precipitation reaction below. Ag⁺(aq)+Br−(aq)→ AgBr(s)
Substance
ΔfG°(kJ/mol)at 298 K
Br−(aq)
-104.0
Ag⁺(aq)
77)12
AgBr(s)
-96)9

A) -70.0 kJ/mol-rxn
B) -123.8 kJ/mol-rxn
C) 70.0 kJ/mol-rxn
D) 123.8 kJ/mol-rxn
E) 84.2 kJ/mol-rxn

Question 55

Calculate Δ_rG° for the reaction below at 25.0 °C. CH₄(g)+ H₂O(g)→ 3 H₂(g)+ CO(g)
Given: Δ_fG° [CH₄(g)] = -50.8 kJ/mol,Δ_fG° [H₂O(g)] = -228.6 kJ/mol,Δ_fG° [H₂(g)] = 0.0 kJ/mol,and Δ_fG° [CO(g)] = -137.2 kJ/mol.

A) -416.3 kJ/mol-rxn
B) -142.2 kJ/mol-rxn
C) +142.2 kJ/mol-rxn
D) +315.0 kJ/mol-rxn
E) +416.3 kJ/mol-rxn

Question 56

The change in entropy for any process is not dependent upon the pathway by which the process occurs.In other words,the change in entropy for any process is a(n)_____ function.

Question 57

The total entropy of the universe is always increasing.This is a statement of the _____ law of thermodynamics.

Question 58

Calculate Δ_rG° for the reaction below at 425 °C, 2 HI(g) H₂(g)+ I₂(g); K = 0.018.(R = 8.314 J/K⋅mol)

A) 6.12 × 10³ kJ/mol-rxn
B) 1.05 × 10⁴ kJ/mol-rxn
C) 1.42 × 10⁴ kJ/mol-rxn
D) 2.33 × 10⁴ kJ/mol-rxn
E) 3.34 × 10⁵ kJ/mol-rxn

Question 59

Determine Δ_fG° at 298 K for SnO using the data below. Sn(s)+ SnO₂(s)→ 2SnO(s)
Given: Δ_rG° = 12.0 kJ/mol-rxn at 298K.
Substance
Δ_fG°(kJ/mol)at 298 K
SnO(s)
?
SnO₂(s)
-515.8

A) -251.9 kJ/mol
B) -503.8 kJ/mol
C) 527.8 kJ/mol
D) 263.9 kJ/mol
E) 1055.6 kJ/mol

Question 60

Which of the following relationships is not true?

A)
B)
C)
D)
E)

Question 61

Does the formation of complex molecules such as proteins and nucleic acids from more simple molecules contradict the second law of thermodynamics?

Question 62

Which of the following statements about entropy is true?

A) The entropy of a substance will increase on going from a solid to a liquid to a gas.
B) The entropy of any substance increases as the temperature is lowered.
C) The entropy of a gas is independent of the volume of the gas.
D) The entropy of a gas decreases with an increase in volume.
E) The entropy of a substance increases with a decrease in the number of moles.

Question 63

At a temperature (in kelvin units)of _____,the entropy of a pure crystal is 0.0 J/K.

Question 64

A reaction is said to be under thermodynamic control when _____.

A) thermodynamics is controlling the ratio of products
B) the ratio of products is the same at all temperatures
C) thermodynamics is controlling the speed of the reaction
D) the ratio of reactants is equal to the ratio of products
E) there are both acidic and basic reactants in a reaction

Question 65

For any process,the change in entropy of the universe equals the sum of the entropy changes for the system and for the ________.

Question 66

Calculate the enthalpy of vaporization of water at its normal boiling point.ΔS° [H₂O( )] = 69.9 J/K⋅mol and ΔS° [H₂O(g)] = 188.8 J/K⋅mol.