Question 1

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 2

What is the relationship between ΔG,Qp,and Kp for a reaction involving gases?

Accepted Answer

A) ΔG = Qp/Kp 
B) ΔG = Kp/Qp 
C) ΔG = RTln(Qp/Kp) 
D) ΔG = RTln(Kp/Qp) 
A) ΔG = Qp/Kp 
B) ΔG = Kp/Qp 
C) ΔG = RTln(Qp/Kp) 
D) ΔG = RTln(Kp/Qp)

Question 3

Which of the following processes is non-spontaneous at standard temperature and pressure?

Accepted Answer

A) Iron metal,oxygen,and water form rust (Fe2O3). 
B) Melting of solid ice to ice water. 
C) Diffusion of perfume molecules across a room. 
D) A reaction at equilibrium moves to non-equilibrium. 
A) Iron metal,oxygen,and water form rust (Fe2O3). 
B) Melting of solid ice to ice water. 
C) Diffusion of perfume molecules across a room. 
D) A reaction at equilibrium moves to non-equilibrium.

Question 4

The figure represents the spontaneous evaporation of nitrogen in which liquid nitrogen,N2(l),becomes gaseous nitrogen,N2(g): N2(l)→ N2(g).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 5

If the entropy of a collection of molecules in 5000 boxes is 1.76 × 10-20 J/K,how many molecules are there?

Accepted Answer

Question 6

The reaction A(g)→ B(g)is spontaneous under standard conditions.Which of the following statements must be true? I.The reaction B(g)→ A(g)is nonspontaneous under standard conditions.
II.A(g)will be completely converted to B(g)if sufficient time is allowed.
III.A(g)will be completely converted to B(g)rapidly.

Accepted Answer

A) none of these 
B) I 
C) I and II 
D) I,II,and III 
A) none of these 
B) I 
C) I and II 
D) I,II,and III

Question 7

At 25°C,ΔG°f is -620 kJ/mol for SiCl4(g)and -592 kJ/mol for MgCl2(s).Calculate ΔG° for the reaction,SiCl4(g)+ 2 Mg(s)→ 2 MgCl2(s)+ Si(s)and determine if the reaction is spontaneous at 25°C if the pressure of SiCl4(g)is 1 atm.

Accepted Answer

A) ΔG° = 28 kJ;the process is spontaneous. 
B) ΔG° = 28 kJ;the process is nonspontaneous. 
C) ΔG° = -564 kJ;the process is spontaneous. 
D) ΔG° = -564 kJ;the process is nonspontaneous. 
A) ΔG° = 28 kJ;the process is spontaneous. 
B) ΔG° = 28 kJ;the process is nonspontaneous. 
C) ΔG° = -564 kJ;the process is spontaneous. 
D) ΔG° = -564 kJ;the process is nonspontaneous.

Question 8

Consider the reaction 2A(g)⇌ AS1U1B12S1U1B0(g).The following pictures represent two possible initial states and the equilibrium state of the system.  
-What are the signs (+ or -)of ΔH,ΔS,and ΔG when the system spontaneously goes from initial state 1 to the equilibrium state?

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 9

According to the third law of thermodynamics,

Accepted Answer

A) energy is conserved in any transformation of matter. 
B) the entropy increases for any spontaneous process. 
C) the entropy of a perfectly ordered,crystalline substance is zero at 0 Kelvin. 
D) the entropy of the universe increases for any spontaneous process. 
A) energy is conserved in any transformation of matter. 
B) the entropy increases for any spontaneous process. 
C) the entropy of a perfectly ordered,crystalline substance is zero at 0 Kelvin. 
D) the entropy of the universe increases for any spontaneous process.

Question 10

Standard molar entropies,S°,in J/K∙mol,are given below each reactant and product in the reaction shown below.The standard entropy of reaction,ΔS°,for this reaction is ________ J/K.
CH4(g)+ 2 O2(g)→ CO2(g)+ 2 H2O(l)
186.2 205.0 213.6 69.9

Accepted Answer

Question 11

ΔG = ΔG° for a reaction

Accepted Answer

A) if Q = K. 
B) if Q = 1. 
C) at STP. 
D) at the start of the reaction. 
A) if Q = K. 
B) if Q = 1. 
C) at STP. 
D) at the start of the reaction.

Question 12

What is the entropy change associated with the expansion of one mole of an ideal gas from an initial volume of V to a final volume of 2.50V at constant temperature?

Accepted Answer

A) ΔS = 2.50 R ln (Vf/Vi) 
B) ΔS = -2.50 R ln (Vf/Vi) 
C) ΔS = R ln 2.50 
D) ΔS = -R ln 2.50 
A) ΔS = 2.50 R ln (Vf/Vi) 
B) ΔS = -2.50 R ln (Vf/Vi) 
C) ΔS = R ln 2.50 
D) ΔS = -R ln 2.50

Question 13

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 14

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 15

What is K if ΔG° = -19.0 kJ for a reaction at 25°?

Accepted Answer

A) 2.10 × 103 
B) 2.80 × 102 
C) 1.80 × 10-3 
D) 5.30 × 10-4 
A) 2.10 × 103 
B) 2.80 × 102 
C) 1.80 × 10-3 
D) 5.30 × 10-4

Question 16

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 17

The reaction 2 H2O(g)+ CO2(g)→ CH4(g)+ 2 CO2(g)is nonspontaneous 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 18

Calculate ΔS° for the formation of three moles of solid sodium bromide from the elements at 25°C.

Accepted Answer

A) -350.1 J/K 
B) -243.6 J/K 
C) -121.5 J/K 
D) 260.4 J/K 
A) -350.1 J/K 
B) -243.6 J/K 
C) -121.5 J/K 
D) 260.4 J/K

Question 19

Which of the following is zero at 25°C?

Accepted Answer

A) ΔG°f for O2(g) 
B) ΔG°f for H2Se (l) 
C) S° for O2 (g) 
D) S° for H2S (l) 
A) ΔG°f for O2(g) 
B) ΔG°f for H2Se (l) 
C) S° for O2 (g) 
D) S° for H2S (l)

Question 20

Consider the following gas-phase reaction of AS1U1B12S1U1B0 (shaded spheres)and BS1U1B12S1U1B0 (unshaded spheres):
AS1U1B12S1U1B0(g)+ BS1U1B12S1U1B0(g)⇌ 2 AB(g)ΔG ° = +25 kJ  
-Which of the above reaction mixtures has the least spontaneous forward reaction?

Accepted Answer

A) (1) 
B) (2) 
C) (3) 
D) (4) 
A) (1) 
B) (2) 
C) (3) 
D) (4)

Exam 17: Thermodynamics: Entropy, free Energy, and Equilibrium

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

What is the relationship between ΔG,Qp,and Kp for a reaction involving gases?

Which of the following processes is non-spontaneous at standard temperature and pressure?

The figure represents the spontaneous evaporation of nitrogen in which liquid nitrogen,N2(l),becomes gaseous nitrogen,N2(g): N2(l)→ N2(g).What are the signs (+ or -)of ΔH,ΔS,and ΔG for this process?

If the entropy of a collection of molecules in 5000 boxes is 1.76 × 10-20 J/K,how many molecules are there?

At 25°C,ΔG°f is -620 kJ/mol for SiCl4(g)and -592 kJ/mol for MgCl2(s).Calculate ΔG° for the reaction,SiCl4(g)+ 2 Mg(s)→ 2 MgCl2(s)+ Si(s)and determine if the reaction is spontaneous at 25°C if the pressure of SiCl4(g)is 1 atm.

Consider the reaction 2A(g)⇌ A2(g).The following pictures represent two possible initial states and the equilibrium state of the system. -What are the signs (+ or -)of ΔH,ΔS,and ΔG when the system spontaneously goes from initial state 1 to the equilibrium state?

According to the third law of thermodynamics,

Standard molar entropies,S°,in J/K∙mol,are given below each reactant and product in the reaction shown below.The standard entropy of reaction,ΔS°,for this reaction is ________ J/K. CH4(g)+ 2 O2(g)→ CO2(g)+ 2 H2O(l) 186.2 205.0 213.6 69.9

ΔG = ΔG° for a reaction

What is the entropy change associated with the expansion of one mole of an ideal gas from an initial volume of V to a final volume of 2.50V at constant temperature?

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.

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).

What is K if ΔG° = -19.0 kJ for a reaction at 25°?

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

The reaction 2 H2O(g)+ CO2(g)→ CH4(g)+ 2 CO2(g)is nonspontaneous 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.

Calculate ΔS° for the formation of three moles of solid sodium bromide from the elements at 25°C.

Which of the following is zero at 25°C?

Consider the following gas-phase reaction of A2 (shaded spheres)and B2 (unshaded spheres): A2(g)+ B2(g)⇌ 2 AB(g)ΔG ° = +25 kJ -Which of the above reaction mixtures has the least spontaneous forward reaction?

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

What is the relationship between ΔG,Q_p,and K_p for a reaction involving gases?

The figure represents the spontaneous evaporation of nitrogen in which liquid nitrogen,N₂(l),becomes gaseous nitrogen,N₂(g): N₂(l)→ N₂(g).What are the signs (+ or -)of ΔH,ΔS,and ΔG for this process?

If the entropy of a collection of molecules in 5000 boxes is 1.76 × 10^-20 J/K,how many molecules are there?

At 25°C,ΔG°_fis -620 kJ/mol for SiCl₄(g)and -592 kJ/mol for MgCl₂(s).Calculate ΔG° for the reaction,SiCl₄(g)+ 2 Mg(s)→ 2 MgCl₂(s)+ Si(s)and determine if the reaction is spontaneous at 25°C if the pressure of SiCl₄(g)is 1 atm.

Consider the reaction 2A(g)⇌ A₂(g).The following pictures represent two possible initial states and the equilibrium state of the system. -What are the signs (+ or -)of ΔH,ΔS,and ΔG when the system spontaneously goes from initial state 1 to the equilibrium state?

Standard molar entropies,S°,in J/K∙mol,are given below each reactant and product in the reaction shown below.The standard entropy of reaction,ΔS°,for this reaction is ________ J/K. CH₄(g)+ 2 O₂(g)→ CO₂(g)+ 2 H₂O(l) 186.2 205.0 213.6 69.9

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.

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?

The reaction 2 H₂O(g)+ CO₂(g)→ CH₄(g)+ 2 CO₂(g)is nonspontaneous 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.

Consider the following gas-phase reaction of A₂ (shaded spheres)and B₂ (unshaded spheres): A₂(g)+ B₂(g)⇌ 2 AB(g)ΔG ° = +25 kJ -Which of the above reaction mixtures has the least spontaneous forward reaction?