Question 1

Which one of the following has the lowest standard molar entropy,S°,at 25°C?

Accepted Answer

A) C8H18(s) 
B) C8H18(l) 
C) C12H26(s) 
D) C12H26(l) 
A) C8H18(s) 
B) C8H18(l) 
C) C12H26(s) 
D) C12H26(l) A

Question 2

The most common white pigment until the 1880s was lead white,sometimes called basic lead carbonate: (PbCO3)2Pb(OH)2.Paintings containing lead white turned black in the presence of moist H2S from natural sources and polluted air due to the formation of PbS.The PbCO3 portion of this reaction is shown below.
PbCO3(s)+ H2S(aq)→ PbS(s)+ H2CO3(aq)
If ΔH° = -60.9 kJ/mol and ΔS° = 26.6 J/K,what are ΔSsurr and ΔStotal for this reaction at 25°C??

Accepted Answer

204 J/K,230 J/K

Question 3

Predict the sign of ΔS for each of the following systems,which occur at constant temperature
I.The volume of 2.0 moles of O2(g)increases from 44 L to 52 L.
II.The pressure of 2.0 moles of O2(g)increases from 1.0 atm to 1.2 atm.

Accepted Answer

A) I: ΔS = negative;II: ΔS = negative 
B) I: ΔS = negative;II: ΔS = positive 
C) I: ΔS = positive;II: ΔS = negative 
D) I: ΔS = positive;II: ΔS = positive 
A) I: ΔS = negative;II: ΔS = negative 
B) I: ΔS = negative;II: ΔS = positive 
C) I: ΔS = positive;II: ΔS = negative 
D) I: ΔS = positive;II: ΔS = positive C

Question 4

Which of the following is true?

Accepted Answer

A) As a reaction at constant temperature and pressure goes to equilibrium,|ΔG| decreases. 
B) The larger ΔG°,the faster the reaction. 
C) The standard state for solutes is the pure solute at 1 atm. 
D) When a reaction reaches equilibrium,ΔG° = 0. 
A) As a reaction at constant temperature and pressure goes to equilibrium,|ΔG| decreases. 
B) The larger ΔG°,the faster the reaction. 
C) The standard state for solutes is the pure solute at 1 atm. 
D) When a reaction reaches equilibrium,ΔG° = 0.

Question 5

The reaction 2 H2(g)+ O2(g)→ 2 H2O(g)is spontaneous at 25°C.The addition of a catalyst will ________ (decrease,increase,not change)the rate of reaction and ________ (decrease,increase,not change)the spontaneity of the reaction.

Accepted Answer

Question 6

For the reaction N2(g)+ 2 O2(g)→ 2 NO2(g),ΔG° = 102.6 kJ.At 25°C the equilibrium constant Kp = ________.

Accepted Answer

Question 7

Which has the lowest entropy?

Accepted Answer

A) CH3OH(s,-25°
C)  
B) CH3OH(s,-15°
C)  
C) CH3OH(l,15°
C)  
D) CH3OH(l,25°
C)  
A) CH3OH(s,-25°
C)  
B) CH3OH(s,-15°
C)  
C) CH3OH(l,15°
C)  
D) CH3OH(l,25°
C)

Question 8

For bromine,ΔH°vap = 30.91 kJ/mol and ΔS°vap = 93.23 JK-1mol-1 at 25°C.What is the normal boiling point for bromine?

Accepted Answer

A) 25°C 
B) 58°C 
C) 124°C 
D) 332°C 
A) 25°C 
B) 58°C 
C) 124°C 
D) 332°C

Question 9

If ΔG° is positive for a reaction,

Accepted Answer

A) K  1. 
A) K  1.

Question 10

Solid NaHCO3 is heated to 90°C.At equilibrium the total pressure of the gases produced is 0.545 atm.Calculate ΔG° at 90°C for the reaction
2 NaHCO3(s)⇌ Na2CO3(s)+ H2O(g)+ CO2(g).

Accepted Answer

A) -7.85 kJ 
B) -3.67 kJ 
C) +3.67 kJ 
D) +7.85 kJ 
A) -7.85 kJ 
B) -3.67 kJ 
C) +3.67 kJ 
D) +7.85 kJ

Question 11

During perspiration,

Accepted Answer

A) the entropy of the water evaporated decreases and the entropy of the body decreases. 
B) the entropy of the water evaporated decreases and the entropy of the body increases. 
C) the entropy of the water evaporated increases and the entropy of the body decreases. 
D) the entropy of the water evaporated increases and the entropy of the body increases. 
A) the entropy of the water evaporated decreases and the entropy of the body decreases. 
B) the entropy of the water evaporated decreases and the entropy of the body increases. 
C) the entropy of the water evaporated increases and the entropy of the body decreases. 
D) the entropy of the water evaporated increases and the entropy of the body increases.

Question 12

By what factor does the entropy increase for a collection of 100 molecules from a system of 1 × 105 boxes to 1 × 106 boxes?

Accepted Answer

Question 13

At high temperatures,boron carbide vaporizes according to
B4C(s)⇌ 4 B(g)+ C(s)
At 2500 K,the equilibrium pressure of B(g)is 0.0342 mm Hg over a mixture of 0.300 mol B4C(s)and 0.500 mol C(s).Calculate ΔG° for this process.

Accepted Answer

A) 832 kJ 
B) 799 kJ 
C) 281 kJ 
D) 247 kJ 
A) 832 kJ 
B) 799 kJ 
C) 281 kJ 
D) 247 kJ

Question 14

The figure below represents the spontaneous reaction of HS1U1B12S1U1B0 (shaded spheres)with OS1U1B12S1U1B0 (unshaded spheres)to produce gaseous HS1U1B12S1U1B0O.  
-What are the signs (+,or -)of ΔH,ΔS,and ΔG for this process?

Accepted Answer

A) ΔH = +,ΔS = +,ΔG = + 
B) ΔH = +,ΔS = +,ΔG = - 
C) ΔH = -,ΔS = -,ΔG = + 
D) ΔH = -,ΔS = -,ΔG = - 
A) ΔH = +,ΔS = +,ΔG = + 
B) ΔH = +,ΔS = +,ΔG = - 
C) ΔH = -,ΔS = -,ΔG = + 
D) ΔH = -,ΔS = -,ΔG = -

Question 15

For the reaction 3 C2H2(g)→ C6H6(l)at 25°C,the standard enthalpy change is -631 kJ and the standard entropy change is -430 J/K.Calculate the standard free energy change at 25°C.

Accepted Answer

A) 948 kJ 
B) -503 kJ 
C) -618 kJ 
D) -1061 kJ 
A) 948 kJ 
B) -503 kJ 
C) -618 kJ 
D) -1061 kJ

Question 16

For a particular process ΔG is less than ΔH.Therefore

Accepted Answer

A) ΔS is positive. 
B) ΔS is negative. 
C) ΔS is zero. 
D) ΔS is negative if ΔH is positive and ΔS is positive if ΔH is negative. 
A) ΔS is positive. 
B) ΔS is negative. 
C) ΔS is zero. 
D) ΔS is negative if ΔH is positive and ΔS is positive if ΔH is negative.

Question 17

An ideal gas is expanded at constant temperature.What are the signs (+,-,or 0)of ΔH,ΔS,and ΔG for this system?

Accepted Answer

A) ΔH = +,ΔS = -,ΔG = + 
B) ΔH = 0,ΔS = +,ΔG = - 
C) ΔH = 0,ΔS = -,ΔG = + 
D) ΔH = -,ΔS = +,ΔG = - 
A) ΔH = +,ΔS = -,ΔG = + 
B) ΔH = 0,ΔS = +,ΔG = - 
C) ΔH = 0,ΔS = -,ΔG = + 
D) ΔH = -,ΔS = +,ΔG = -

Question 18

Which substance has the highest standard molar entropy at 25°C?

Accepted Answer

A) C(graphite) 
B) C2H4(g) 
C) CH3OH(l) 
D) MgCO3(s) 
A) C(graphite) 
B) C2H4(g) 
C) CH3OH(l) 
D) MgCO3(s)

Question 19

In general,as a reaction goes to equilibrium

Accepted Answer

A) ΔG decreases. 
B) ΔG°f decreases. 
C) ΔG goes to zero. 
D) ΔG° decreases. 
A) ΔG decreases. 
B) ΔG°f decreases. 
C) ΔG goes to zero. 
D) ΔG° decreases.

Question 20

The standard free energy for a reaction is ΔG° = -33.0 kJ.At 25°C the equilibrium constant for this reaction,Kp = ________.

Accepted Answer

Exam 16: Thermodynamics: Entropy, free Energy, and Equilibrium

Which one of the following has the lowest standard molar entropy,S°,at 25°C?

Predict the sign of ΔS for each of the following systems,which occur at constant temperature I.The volume of 2.0 moles of O2(g)increases from 44 L to 52 L. II.The pressure of 2.0 moles of O2(g)increases from 1.0 atm to 1.2 atm.

Which of the following is true?

The reaction 2 H2(g)+ O2(g)→ 2 H2O(g)is spontaneous at 25°C.The addition of a catalyst will ________ (decrease,increase,not change)the rate of reaction and ________ (decrease,increase,not change)the spontaneity of the reaction.

For the reaction N2(g)+ 2 O2(g)→ 2 NO2(g),ΔG° = 102.6 kJ.At 25°C the equilibrium constant Kp = ________.

Which has the lowest entropy?

For bromine,ΔH°vap = 30.91 kJ/mol and ΔS°vap = 93.23 JK-1mol-1 at 25°C.What is the normal boiling point for bromine?

If ΔG° is positive for a reaction,

Solid NaHCO3 is heated to 90°C.At equilibrium the total pressure of the gases produced is 0.545 atm.Calculate ΔG° at 90°C for the reaction 2 NaHCO3(s)⇌ Na2CO3(s)+ H2O(g)+ CO2(g).

During perspiration,

By what factor does the entropy increase for a collection of 100 molecules from a system of 1 × 105 boxes to 1 × 106 boxes?

At high temperatures,boron carbide vaporizes according to B4C(s)⇌ 4 B(g)+ C(s) At 2500 K,the equilibrium pressure of B(g)is 0.0342 mm Hg over a mixture of 0.300 mol B4C(s)and 0.500 mol C(s).Calculate ΔG° for this process.

The figure below represents the spontaneous reaction of H2 (shaded spheres)with O2 (unshaded spheres)to produce gaseous H2O. -What are the signs (+,or -)of ΔH,ΔS,and ΔG for this process?

For the reaction 3 C2H2(g)→ C6H6(l)at 25°C,the standard enthalpy change is -631 kJ and the standard entropy change is -430 J/K.Calculate the standard free energy change at 25°C.

For a particular process ΔG is less than ΔH.Therefore

An ideal gas is expanded at constant temperature.What are the signs (+,-,or 0)of ΔH,ΔS,and ΔG for this system?

Which substance has the highest standard molar entropy at 25°C?

In general,as a reaction goes to equilibrium

The standard free energy for a reaction is ΔG° = -33.0 kJ.At 25°C the equilibrium constant for this reaction,Kp = ________.

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Predict the sign of ΔS for each of the following systems,which occur at constant temperature I.The volume of 2.0 moles of O₂(g)increases from 44 L to 52 L. II.The pressure of 2.0 moles of O₂(g)increases from 1.0 atm to 1.2 atm.

The reaction 2 H₂(g)+ O₂(g)→ 2 H₂O(g)is spontaneous at 25°C.The addition of a catalyst will (decrease,increase,not change)the rate of reaction and (decrease,increase,not change)the spontaneity of the reaction.

For the reaction N₂(g)+ 2 O₂(g)→ 2 NO₂(g),ΔG° = 102.6 kJ.At 25°C the equilibrium constant K_p = ________.

For bromine,ΔH°vap = 30.91 kJ/mol and ΔS°vap = 93.23 JK^-1mol^-1 at 25°C.What is the normal boiling point for bromine?

Solid NaHCO₃ is heated to 90°C.At equilibrium the total pressure of the gases produced is 0.545 atm.Calculate ΔG° at 90°C for the reaction 2 NaHCO₃(s)⇌ Na₂CO₃(s)+ H₂O(g)+ CO₂(g).

By what factor does the entropy increase for a collection of 100 molecules from a system of 1 × 10⁵ boxes to 1 × 10⁶ boxes?

At high temperatures,boron carbide vaporizes according to B₄C(s)⇌ 4 B(g)+ C(s) At 2500 K,the equilibrium pressure of B(g)is 0.0342 mm Hg over a mixture of 0.300 mol B₄C(s)and 0.500 mol C(s).Calculate ΔG° for this process.

The figure below represents the spontaneous reaction of H₂ (shaded spheres)with O₂ (unshaded spheres)to produce gaseous H₂O. -What are the signs (+,or -)of ΔH,ΔS,and ΔG for this process?

For the reaction 3 C₂H₂(g)→ C₆H₆(l)at 25°C,the standard enthalpy change is -631 kJ and the standard entropy change is -430 J/K.Calculate the standard free energy change at 25°C.

The standard free energy for a reaction is ΔG° = -33.0 kJ.At 25°C the equilibrium constant for this reaction,K_p = ________.