Deck 14: Chemical Equilibrium

Question 1

Which of the following is true about a system that has reached chemical equilibrium:

A) the net concentrations of products and reactants are not changing
B) there is a dynamic balance between forward and reverse processes
C) the concentration of the products equals that of the reactants
D) a and b
E) a and c

Answer 1

D

Question 2

Which of the following is a true statement:

A) K, K_p, and K_c can all be dimensionless quantities
B) K will always have the same dimension as K_p
C) K_P can never equal K_c
D) It is not possible to calculate K with only thermodynamic tables

Answer 2

A

Question 3

Under what circumstances will K_p = K

A) K_p can never numerically equal K
B) K_p is always numerically equal to K
C) K_p will equal K when pressures are recorded in Torr and P_ref = 760
D) K_p will equal K when pressures are recorded in the Pascals (SI Units)

Answer 3

C

Question 4

Under what circumstances will K_c = K

A) K_c equals K when molar concentration units are used and C_ref = 1M
B) K_c equals K when molal concentrations are used and C_ref = 1m
C) K_c will equal K only in very dilute solution
D) a and c

Question 5

Which of the following is a true statement

A) Q_c can approach K_C, but never equal K_c
B) If Q_c > K_c, reactants will be favored
C) if Q_c < K_c, reactants will be favored
D) a and b
E) a and c

Question 6

It is determined that a certain reaction between two aqueous species is exothermic and produces at least one product that is a gas. Which set of reaction conditions would most decrease the yield of product?

A) High temperature, low pressure
B) Low temperature, high pressure
C) High temperature, high pressure
D) Low temperature, low pressure

Question 7

Which of the following is temperature dependant

A) K_P
B) K_C
C) partition coefficients
D) activity coefficients
E) all of the above

Question 8

Consider the following reaction in aqueous solution:
2A + 3B + C D + E
Which of the following is the correct law of mass action for this reaction?

A) K_c=[2A][3B][C][D]^-1[E]^-1
B) K_c=[A]²[B]³[C] \ [D][E]
C) K_c=[A]^-2[B]^-3[C]^-1[D][E]
D) K_c=[D][E] / [A]^-2[B]^-3[C]

Question 9

Equal volumes of two immiscible liquids, A and B, are placed in a separatory funnel. A small amount of solute (S) is dissolved in the liquids and is partitioned between the A and B layers with a partition coefficient of [S]_A / [S]_B=0.6. If liquid B is removed from the flask, will the concentration of S remaining in the flask be

A) greater than the initial concentration
B) less than the initial concentration
C) equal to the initial concentration
D) impossible to determine

Question 10

The greater the value of the partition ratio K of the solute between the stationary phase and the mobile phase of a chromatographic column:

A) The slower the solute travels through the stationary phase of the column
B) The faster the solute travels through the stationary phase of the column
C) There is no difference in the rate or travel of the solute, the rate of travel is based solely on the mobile phase
D) a and c
E) b and c

Question 11

A certain chemical reaction sets up an equilibrium as follows:
A₂(g) + 3B₂(g) 2AB₃(g)
At a certain temperature equilibrium is established with equilibrium partial pressures for A₂, B₂, and AB₃ of 0.11, 0.34, and 1.33 atm respectively. What is the value of the equilibrium constant at this temperature?

A) 410
B) 355
C) 0.0281
D) There is not enough information to answer the question
E) None of the above

Question 12

At 25°C, Kp=2.86×10²⁴ for the reaction:
2SO₂(g) + O₂(g) 2SO₃(g)
At this temperature, what is the value of Kp for the reaction
SO₃(g) SO₂(g) + O₂(g)

A) 1.69×10¹²
B) 5.91×10^-13
C) 2.86×10²⁴
D) 3.50×10^-25
E) There is not enough information to answer the question

Question 13

Exhibit 14-1
The following question(s) pertain to the equilibrium 2NO(g) + 2H₂(g) → N₂(g) + 2H₂O(g) with initial partial pressures of P_NO=0.3 atm, =0.4 atm, =0.4 atm.
Refer to Exhibit 14-1. At a certain temperature equilibrium is established and it is determined that the partial pressure of water is 0.228 atm. What are the equilibrium partial pressures of NO, H2, and N2 respectively?

A) 0.172 atm, 0.172 atm, 0.472 atm
B) 0.192 atm, 0.192 atm, 0.466 atm,
C) 0.578 atm, 0.172 atm, 0.578 atm
D) 0.114 atm, 0.114 atm, 0.472 atm

Question 14

Exhibit 14-1
The following question(s) pertain to the equilibrium 2NO(g) + 2H₂(g) → N₂(g) + 2H₂O(g) with initial partial pressures of P_NO=0.3 atm, =0.4 atm, =0.4 atm.
Refer to Exhibit 14-1. What is the numerical value of the equilibrium constant Kp at this temperature

A) 3.63
B) .275
C) 28.0
D) .483
E) None of the above

Question 15

Exhibit 14-1
The following question(s) pertain to the equilibrium 2NO(g) + 2H₂(g) → N₂(g) + 2H₂O(g) with initial partial pressures of P_NO=0.3 atm, =0.4 atm, =0.4 atm.
Refer to Exhibit 14-1. What is the numerical value of the thermodynamic equilibrium constant K at this temperature

A) 28.0
B) 3.63
C) 1.13
D) .483
E) Not enough information is given to answer the question

Question 16

At 100 C, the following two reactions have the denoted equilibrium constants.
2NO(g) + Br ₂(g) 2NOBr(g) K=2.4
Br²(g) + Cl2(g) 2BrCl(g) K=7.5
What is the value of the equilibrium constant for the reaction?
2NOBr(g) + C_l2(g) 2NO(g) + 2BrCl(g)

A) 180
B) 0.055
C) 3.125
D) .320
E) None of the above

Question 17

At 600 K, the enthalpy of a certain reaction is -22 kJ with an equilibrium constant of 4500. What will be the value of the equilibrium constant at 300 K?

A) 0.0121
B) 54.7
C) .3203.7×10⁵
D) Not enough information is given to answer the question
E) None of the above

Question 18

A certain endothermic reaction is known to have an equilibrium constant of 50 at 100 K. What can you say about the value of the equilibrium constant at 298 K?

A) It will be less that 50
B) It will be greater than 50
C) It will equal 50
D) Not enough information is given to answer the question
E) None of the above

Question 19

A researcher constructed a reaction vessel and connected it to a spectrophotometer so that the concentrations of all species in the vessel could be measured simultaneously. At 25°C all of the concentrations were measured and the equilibrium constant (K_c) was calculated to be 3445. The temperature was increased to 75°C, the concentrations measured, and the equilibrium constant calculated to be 9015. What is the DH_rxn?

A) -45.1 kJ
B) 45.1 kJ
C) -16.6 kJ
D) -7.2 kJ
E) None of the above

Question 20

At 50°C the thermodynamic equilibrium constant for the reaction
2NO₂(g) N₂O₄(g)
Is 1.18. If a reaction vessel is initially charged with 0.5 atm of NO₂ at this temperature. What will be the partial pressure of N₂O₄ be when the reaction reaches equilibrium?

A) 0.102 atm
B) 0.147 atm
C) 0.175 atm
D) 0.270 atm
E) None of the above

Question 21

Fifty grams of solid I₂ is placed in a 1 liter evacuated cell and allowed to come to equilibrium with its vapor at 120°C. What is the partial pressure of I₂ vapor in the cell when it reaches equilibrium?

A) 18 Torr
B) 134 Torr
C) 299 Torr
D) 790 Torr
E) None of the above

Question 22

Exhibit 14-2
The following question(s) pertain to the reaction H₂(g) + I₂(g) 2HI(g) at 150°C with the reaction vessel being charged in such a way that the initial partial pressure of all the species in the reaction (both reactants and products) is 0.200 atm.
Refer to Exhibit 14-2. What is the value of the equilibrium constant at this temperature?

A) 8.65×10^-15
B) 204
C) 10.2
D) 1.00
E) None of the above

Question 23

Exhibit 14-2
The following question(s) pertain to the reaction H₂(g) + I₂(g) 2HI(g) at 150°C with the reaction vessel being charged in such a way that the initial partial pressure of all the species in the reaction (both reactants and products) is 0.200 atm.
Refer to Exhibit 14-2. What is the value of Q?

A) 1.00
B) 5.00
C) 0.200
D) 0.100
E) None of the above

Question 24

Exhibit 14-2
The following question(s) pertain to the reaction H₂(g) + I₂(g) 2HI(g) at 150°C with the reaction vessel being charged in such a way that the initial partial pressure of all the species in the reaction (both reactants and products) is 0.200 atm.
Refer to Exhibit 14-2. Based on the equilibrium constant and the value of Q, will more reactants or products be formed as the system approaches equilibrium at this temperature?

A) More products will be formed
B) More reactants will be formed
C) Not enough data to answer the question
D) None of the above

Question 25

Exhibit 14-2
The following question(s) pertain to the reaction H₂(g) + I₂(g) 2HI(g) at 150°C with the reaction vessel being charged in such a way that the initial partial pressure of all the species in the reaction (both reactants and products) is 0.200 atm.
Refer to Exhibit 14-2. What will be the partial pressure of HI when the system reaches equilibrium?

A) 0.200 atm
B) 0.037 atm
C) 0.526 atm
D) 0.373 atm
E) Not enough data to answer the question

Question 26

Exhibit 14-2
The following question(s) pertain to the reaction H₂(g) + I₂(g) 2HI(g) at 150°C with the reaction vessel being charged in such a way that the initial partial pressure of all the species in the reaction (both reactants and products) is 0.200 atm.
Refer to Exhibit 14-2. What will be the total pressure in the reaction cell when the system reaches equilibrium?

A) 0.200 atm
B) 0.374 atm
C) 0.427 atm
D) 0.600 atm
E) Not enough data to answer the question

Question 27

Exhibit 14-3
The following question(s) pertain to the reaction N₂(g) + 3H₂(g) 2NH₃(g) at 200°C with the reaction vessel being charged in such a way that the initial partial pressures of N₂, H₂, and NH₃ are 0.200, 0.300, and 0.600 atm respectively.
Refer to Exhibit 14-3. What is the value of the equilibrium constant K_p at this temperature?

A) 0.652
B) 2.78×10^-21
C) 3.59×10²⁰
D) 1.92×10^-14
E) None of the above

Question 28

Exhibit 14-3
The following question(s) pertain to the reaction N₂(g) + 3H₂(g) 2NH₃(g) at 200°C with the reaction vessel being charged in such a way that the initial partial pressures of N₂, H₂, and NH₃ are 0.200, 0.300, and 0.600 atm respectively.
Refer to Exhibit 14-3. What is the value of Q?

A) 10
B) 1
C) 1670
D) 67
E) None of the above

Question 29

Exhibit 14-3
The following question(s) pertain to the reaction N₂(g) + 3H₂(g) 2NH₃(g) at 200°C with the reaction vessel being charged in such a way that the initial partial pressures of N₂, H₂, and NH₃ are 0.200, 0.300, and 0.600 atm respectively.
Refer to Exhibit 14-3. Based on the equilibrium constant and the value of Q, will more reactants or products be formed as the system approaches equilibrium at this temperature?

A) More products will be formed
B) More reactants will be formed
C) Not enough data to answer the question

Question 30

Exhibit 14-3
The following question(s) pertain to the reaction N₂(g) + 3H₂(g) 2NH₃(g) at 200°C with the reaction vessel being charged in such a way that the initial partial pressures of N₂, H₂, and NH₃ are 0.200, 0.300, and 0.600 atm respectively.
Refer to Exhibit 14-3. What will be the partial pressure of NH₃ when the system reaches equilibrium at this temperature?

A) 0.896 atm
B) 0.305 atm
C) 0.037 atm
D) 0.600 atm
E) None of the above

Question 31

Exhibit 14-3
The following question(s) pertain to the reaction N₂(g) + 3H₂(g) 2NH₃(g) at 200°C with the reaction vessel being charged in such a way that the initial partial pressures of N₂, H₂, and NH₃ are 0.200, 0.300, and 0.600 atm respectively.
Refer to Exhibit 14-3. What will be the total pressure in the reaction vessel when the system reaches equilibrium at this temperature?

A) 1.24 atm
B) 0.900 atm
C) 0.744 atm
D) 0.305 atm
E) None of the above

Question 32

A certain chemical reaction sets up an equilibrium as follows
3A₂(aq) + 2B₃(aq) 6AB(aq)
After being started with unknown amounts of A₂ and B₃. Once the system reaches equilibrium the concentrations of A₂, B₃, and AB are precisely determined. What other quantities can be determined?

A) Q, K_c, K, DG°
B) Q, K_c, DG, DG°
C) Q, K, DG, DG°
D) K, K_c, DG, DG°
E) Q, K_c, K, DG

Question 33

At room temperature cyclohexane exists almost exclusively in the chair conformation (99.99%). But at 800°C, 30% of the cyclohexane molecules exist in the twist-boat conformation.
What is the value of the equilibrium constant for the following reaction at 800°C?
C₆H₁₂(chair) C₆H₁₂(twist-boat)

A) 0.30
B) 0.23
C) 2.3
D) 0.43
E) 0.77

Question 34

At room temperature cyclohexane exists almost exclusively in the chair conformation (99.99%). But at 800°C, 30% of the cyclohexane molecules exist in the twist-boat conformation.
Compared to its value at 25°C, the value of DG° at 800°C for the reaction
C₆H₁₂(chair) C₆H₁₂(twist-boat)
Should

A) be larger in magnitude and have the same sign
B) be larger in magnitude and have the opposite sign
C) be smaller in magnitude and have the same sign
D) be smaller in magnitude and have the opposite sign
E) not enough information to answer the question