Deck 15: Chemical Equilibrium

Question 1

Nitrosyl bromide decomposes according to the following equation.
A sample of NOBr (0.64 mol) was placed in a 1.00- L flask containing no NO or Br₂. At equilibrium the flask contained 0.46 mol of NOBr. How many moles of NO and Br₂, respectively, are in the flask at equilibrium?

A) 0.46, 0.23
B) 0.46, 0.46
C) 0.18, 0.360
D) 0.18, 0.18
E) 0.18, 0.090

Answer 1

0.18, 0.090

Question 2

How is the reaction quotient used to determine whether a system is at equilibrium?

A)The reaction is at equilibrium when Q > K_eq.
B)The reaction is at equilibrium when Q = K_eq.
C)The reaction quotient must be satisfied for equilibrium to be achieved.
D)The reaction is at equilibrium when Q < K_eq.
E)At equilibrium, the reaction quotient is undefined.

Answer 2

The reaction is at equilibrium when Q = K_eq.

Question 3

What role did Karl Bosch play in development of the Haber- Bosch process?

A)He originally isolated ammonia from camel dung and found a method for purifying it.
B)He was the German industrialist who financed the research done by Haber.
C)He discovered the reaction conditions necessary for formation of ammonia.
D)He developed the equipment necessary for industrial production of ammonia.
E)Haber was working in his lab with his instructor at the time he worked out the process.

Answer 3

He developed the equipment necessary for industrial production of ammonia.

Question 4

The equilibrium- constant expression depends on the of the reaction.

A)the quantities of reactants and products initially present
B)stoichiometry and mechanism
C)stoichiometry
D)mechanism
E)temperature

Question 5

The equilibrium- constant expression for the reaction

is given by

A)
B)
C)
D)
E)

Question 6

At 900 K, the equilibrium constant (K_p) for the following reaction is 0.345. 2SO₂ + O₂ (g) -2SO₃ (g)
At equilibrium, the partial pressure of SO₂ is 35.0 atm and that of O₂ is 15.9 atm. The partial pressure of SO₃ is _ atm.

A) 6.20 × 10^{- 4}
B) 192
C) 40.2
D) 82.0
E) 4.21 × 10^{- 3}

Question 7

The K_eq for the equilibrium below is 7.52 × 10^{- 2} at 480 °C.

A) 5.66 × 10^{- 3}

B) 0.150
C) 0.0752
D) - 0.0752
E) 13.3

Question 8

The equilibrium constant for reaction 1 is K. The equilibrium constant for reaction 2 is . (1) SO₂ (g) + (1/2) O₂ (g) SO₃ (g)
(2) 2SO₃ (g) 2SO₂ (g) + O₂ (g)

A) 1/K²
B) K²
C) 2K
D) - K²
E) 1/2K

Question 9

The K_eq for the equilibrium below is 7.52 × 10^{- 2} at 480 °C.
2Cl₂ (g) + 2H2O (g) 4HCl (g) + O₂ (g)
What is the value of K_eq at this temperature for the following reaction?
Cl₂ (g) + H₂O (g) 2HCl (g) + ¹ O₂ (g)

A) 0.274
B) 5.66 × 10^{- 3}
C) 0.150
D) 0.0752
E) 0.0376

Question 10

The equilibrium constant (K_p) for the reaction below is 7.00 × 10^{- 2} at 22 °C: A sample of NH₄HS is placed in an evacuated container and allowed to come to equilibrium. The partial pressure of NH₃ is then increased by the addition of 0.590 atm of NH₃. The partial pressure of H₂S at equilibrium is now atm.

A) 0.691
B) 0.855
C) 0.119
D) 0.265
E) 0.101

Question 11

The equilibrium constant for the gas phase reaction
Is K_eq = 230 at 300 °C. At equilibrium, _ _.

A)products predominate
B)only reactants are present
C)reactants predominate
D)only products are present
E)roughly equal amounts of products and reactants are present

Question 12

The relationship between the rate constants for the forward and reverse reactions and the equilibrium constant for the process is K_eq= .

A)k_f + k_r
B) k_fk_r
C) k_f/k_r
D) k_r/k_f
E) k_f - k_r

Question 13

The K_eq for the equilibrium below is 0.112 at 700 °C. SO₂ (g) + ¹ O₂

A) 79.7
B) 8.93
C) 17.86
D) 4.46
E) 2.99

Question 14

In what year was Fritz Haber awarded the Nobel Prize in chemistry for his development of a process for synthesizing ammonia directly from nitrogen and hydrogen?

A) 1912
B) 1918
C) 1900
D) 1954
E) 1933

Question 15

Consider the following reaction at equilibrium:

Le Cha^{^}telier's principle predicts that adding O₂ (g) to the reaction container will _ .

A)increase the partial pressure of CO (g) at equilibrium
B)increase the partial pressure of CO₂ (g) at equilibrium
C)decrease the partial pressure of CO₂ (g) at equilibrium
D)decrease the value of the equilibrium constant
E)increase the value of the equilibrium constant

Question 16

Consider the following equilibrium.

The equilibrium cannot be established when _ _ is/are placed in a 1.0- L container.

A)0.50 mol O₂ (g) and 0.50 mol SO₃ (g)
B)0.75 mol SO₂ (g)
C)0.25 mol of SO₂ (g) and 0.25 mol of SO₃ (g)
D)1.0 mol SO₃ (g)
E)0.25 mol SO₂ (g) and 0.25 mol O₂ (g)

Question 17

The value of K_eq for the following reaction is 0.25:

A) 0.12
B) 0.062
C) 16
D) 0.25
E) 0.50

Question 18

The K_eq for the equilibrium below is 7.52 × 10^{- 2} at 480 °C.

A) 0.274
B) 3.65
C) - 0.0376
D) 13.3
E) 5.66 × 10^{- 3}

Question 19

Phosphorous trichloride and phosphorous pentachloride equilibrate in the presence of molecular chlorine according to the reaction:
PCl₃ (g) + Cl₂ (g) -PCl₅ (g)
An equilibrium mixture at 450 K contains P_PCl3 = 0.202 atm,
P_Cl2 = 0.256 atm, and
P_PCl5 = 3.45 atm. What is the value of K_p at this temperature?

A) 1.50 × 10^{- 2}
B) 66.8
C) 2.99
D) 7.54
E) 1.78 × 10^{- 1}

Question 20

How does the reaction quotient of a reaction (Q) differ from the equilibrium constant (K_eq) of the same reaction?

A)K does not depend on the concentrations or partial pressures of reaction components.
B)Q does not change with temperature.
C)Q is the same as K_eq when a reaction is at equilibrium.
D)K_eq does not change with temperature, whereas Q is temperature dependent.
E)Q does not depend on the concentrations or partial pressures of reaction components.

Question 21

For the endothermic reaction
CaCO₃ (s) CaO (s) + CO₂ (g)
Le Cha^{^}telier's principle predicts that _ will result in an increase in the number of moles of CO₂.

A)increasing the pressure
B)decreasing the temperature
C)increasing the temperature
D)removing some of the CaCO₃ (s)
E)adding more CaCO₃ (s)

Question 22

The effect of a catalyst on an equilibrium is to .

A)slow the reverse reaction only
B)shift the equilibrium to the right
C)increase the rate of the forward reaction only
D)increase the rate at which equilibrium is achieved without changing the composition of the equilibrium mixture
E)increase the equilibrium constant so that products are favored

Question 23

At 400 K, the equilibrium constant for the reaction Br₂ (g) + Cl₂ (g) 2BrCl (g)
Is K_p = 7.0. A closed vessel at 400 K is charged with 1.00 atm of Br₂ (g), 1.00 atm of Cl₂ (g), and 2.00
Atm of BrCl (g). Use Q to determine which of the statements below is true.

A)At equilibrium, the total pressure in the vessel will be less than the initial total pressure.
B)The equilibrium partial pressures of Br₂, Cl₂, and BrCl will be the same as the initial values.
C)The equilibrium partial pressure of BrCl (g) will be greater than 2.00 atm.
D)The reaction will go to completion since there are equal amounts of Br₂ and Cl₂.
E)The equilibrium partial pressure of Br₂ will be greater than 1.00 atm.

Question 24

The K_p for the reaction below is 1.49 × 10⁸ at 100 °C: CO (g) + Cl₂ (g) -COCl₂ (g)
In an equilibrium mixture of the three gases, P_CO = P_Cl2 = 8.60 × 10^{- 4} atm. The partial pressure of the product, phosgene (COCl₂), is atm.

A) 1.28 × 10⁵
B) 1.72 × 10¹¹
C) 1.10 × 10²
D) 4.96 × 10^{- 15}
E) 2.01 × 10¹⁴

Question 25

The number obtained by substituting starting reactant and product concentrations into an equilibrium- constant expression is known as the .

Question 26

Pure and pure are excluded from equilibrium- constant expressions.

Question 27

Dinitrogentetraoxide partially decomposes according to the following equilibrium:
N₂O₄ (g) -2NO₂ (g)
A 1)000- L flask is charged with 3.00 × 10^{- 2} mol of N₂O₄. At equilibrium, 2.36 × 10^{- 2} mol of N₂O₄ remains. K_eq for this reaction is .

A) 0.391
B) 0.723
C) 6.93 × 10^{- 3}
D) 1.92 × 10^{- 4}
E) 0.212

Question 28

In which of the following reactions would increasing pressure at constant temperature not change the concentrations of reactants and products, based on Le Cha^{^}telier's principle?

A)
B)
C)
D)
E)

Question 29

At equilibrium, .

A)all chemical reactions have ceased
B)the rate constants of the forward and reverse reactions are equal
C)the rates of the forward and reverse reactions are equal
D)the value of the equilibrium constant is 1
E)the limiting reagent has been consumed

Question 30

Which one of the following is true concerning the Haber process?

A)It is a process used for the synthesis of ammonia.
B)It is an industrial synthesis of sodium chloride that was discovered by Karl Haber.
C)It is a process used for shifting equilibrium positions to the right for more economical chemical synthesis of a variety of substances.
D)It is another way of stating LeChatelier's principle.
E)It is a process for the synthesis of elemental chlorine.

Question 31

The equilibrium constant for the gas phase reaction N₂ (g) + 3H₂ (g) 2NH₃ (g)
Is K_eq = 4.34 × 10^{- 3} at 300 °C. At equilibrium, _ _.

A)roughly equal amounts of products and reactants are present
B)reactants predominate
C)only reactants are present
D)products predominate
E)only products are present

Question 32

Consider the following reaction at equilibrium:
2NH₃ (g) N₂ (g) + 3H₂ (g) OH° = +92.4 kJ
Le Cha^{^}telier's principle predicts that adding N₂ (g) to the system at equilibrium will result in

A)a decrease in the concentration of NH₃ (g)
B)removal of all of the H₂ (g)
C)a lower partial pressure of N₂
D)an increase in the value of the equilibrium constant
E)a decrease in the concentration of H₂ (g)

Question 33

Which one of the following will change the value of an equilibrium constant?

A)adding other substances that do not react with any of the species involved in the equilibrium
B)varying the initial concentrations of products
C)changing temperature
D)varying the initial concentrations of reactants
E)changing the volume of the reaction vessel

Question 34

Consider the following reaction at equilibrium:
2CO₂ (g) 2CO (g) + O₂ (g) OH° = - 514 kJ
Le Cha^{^}telier's principle predicts that an increase in temperature will .

A)increase the value of the equilibrium constant
B)decrease the partial pressure of CO₂ (g)
C)decrease the value of the equilibrium constant
D)increase the partial pressure of O₂ (g)
E)increase the partial pressure of CO

Question 35

If the value for the equilibrium constant is much greater than 1, then the equilibrium mixture contains mostly .

Question 36

The reaction below is exothermiC: 2SO₂ (g) + O₂ (g) 2SO₃ (g)
Le Cha^{^}telier's Principle predicts that will result in an increase in the number of moles of
SO₃ (g) in the reaction container.

A)removing some oxygen
B)increasing the volume of the container
C)decreasing the pressure
D)increasing the pressure
E)increasing the temperature

Question 37

Consider the following reaction at equilibrium.
2CO₂ (g) 2CO (g) + O₂ (g) OH° = - 514 kJ
Le Cha^{^}telier's principle predicts that the equilibrium partial pressure of CO (g) can be maximized by carrying out the reaction .

A)at high temperature and high pressure
B)at high temperature and low pressure
C)at low temperature and low pressure
D)at low temperature and high pressure
E)in the presence of solid carbon

Question 38

Consider the following reaction at equilibrium:
2SO₂ (g) + O₂ (g) 2SO₃ (g) OH° = - 99 kJ
Le Cha^{^}telier's principle predicts that an increase in temperature will result in .

A)the partial pressure of O₂ will decrease
B)a decrease in the partial pressure of SO₃
C)a decrease in the partial pressure of SO₂
D)an increase in K_eq
E)no changes in equilibrium partial pressures

Question 39

Exactly 3.5 moles if N₂O₄ is placed in an empty 2.0- L container and allowed to reach equilibrium described by the equation
N₂O₄ (g) "2NO₂ (g)
If at equilibrium the N₂O₄ is 25% dissociated, what is the value of the equilibrium constant for the reaction?

Question 40

The equilibrium- constant expression for a reaction written in one direction is the
of the one for the reaction written for the reverse direction.

Question 41

Dinitrogentetraoxide partially decomposes according to the following equilibrium:
N₂O₄ (g) 2NO₂ (g)
A 1)00- L flask is charged with 0.400 mol of N₂O₄. At equilibrium at 373 K, 0.0055 mol of N₂O₄ remains. K_eq for this reaction is .

A) 2.2 × 10^{- 4}
B) 0.22
C) 0.87
D) 13
E) 0.022

Question 42

The effect of a catalyst on a chemical reaction is to react with product, effectively removing it and shifting the equilibrium to the right.

Question 43

The relationship between the concentrations of reactants and products of a system at equilibrium is given by the law of mass action.

Question 44

At elevated temperatures, molecular hydrogen and molecular bromine react to partially form hydrogen bromide:
H₂ (g) + Br₂ (g) 2HBr (g)
A mixture of 0.682 mol of H₂ and 0.440 mol of Br₂ is combined in a reaction vessel with a volume of 2.00 L. At equilibrium at 700 K, there are 0.566 mol of H₂ present. At equilibrium, there are
Mol of Br₂ present in the reaction vessel.

A) 0.440
B) 0.324
C) 0.000
D) 0.566
E) 0.232

Question 45

Consider the following chemical reaction:
H₂ (g) + I₂ (g) 2HI (g)
At equilibrium in a particular experiment, the concentrations of H₂, I₂, and HI were 0.15 M,
0)033 M, and 0.55 M, respectively. The value of K_eq for this reaction is .

A) 9.0 × 10^{- 3}
B) 61
C) 23
D) 111
E) 6.1

Question 46

At 22 °C, K_p = 0.070 for the equilibrium:
NH₄HS (s) NH₃ (g) + H₂S (g)
A sample of solid NH₄HS is placed in a closed vessel and allowed to equilibrate. Calculate the equilibrium partial pressure (atm) of ammonia, assuming that some solid NH₄HS remains.

A) 0.070
B) 0.26
C) 3.8
D) 0.52
E) 4.9 × 10^{- 3}

Question 47

In an exothermic equilibrium reaction, increasing the reaction temperature favors the formation of reactants.

Question 48

A sealed 1.0 L flask is charged with 0.500 mol of I₂ and 0.500 mol of Br₂. An equilibrium reaction ensues:
I₂ (g) + Br₂ (g) 2IBr (g)
When the container contents achieve equilibrium, the flask contains 0.84 mol of IBr. The value of K_eq is _ .

A) 4.0
B) 2.8
C) 11
D) 6.1
E) 110

Question 49

Acetic acid is a weak acid that dissociates into the acetate ion and a proton in aqueous solution:
HC₂H₃O₂ (aq) C₂H₃O₂^- (aq) + H⁺ (aq)
At equilibrium at 25 °C a 0.100 M solution of acetic acid has the following concentrations:
[HC₂H₃O₂] = 0.0990 M, [C₂H₃O₂^- ] = 1.33 × 10^{- 3} M, and [H⁺] = 1.33 × 10^{- 3} M. The equilibrium
Constant, K_eq, for the ionization of acetic acid at 25 °C is _ .

A) 5.71 × 10⁶
B) 1.75 × 10^{- 7}
C) 1.79 × 10^{- 5}
D) 5.71 × 10⁴
E) 0.100

Question 50

The value of K_eq for the equilibrium
H₂ (g) + I₂ (g) 2 HI (g)
Is 794 at 25 °C. At this temperature, what is the value of K_eq for the equilibrium below?
HI (g) 1/2 H₂ (g) + 1/2 I₂ (g)

A) 0.035
B) 0.0013
C) 1588
D) 397
E) 28

Question 51

The equilibrium constant (K_p) for the interconversion of PCl₅ and PCl₃ is 0.0121:
PCl₅ (g) PCl₃ (g) + Cl₂ (g)
A vessel is charged with PCl₅, giving an initial pressure of 0.123 atm. At equilibrium, the partial Pressure of PCl₃ is _ atm.

A) 0.123
B) 0.078
C) 0.033
D) 0.045
E) 0.090

Question 52

The value of K_eq for the equilibrium
H₂ (g) + I₂ (g) 2 HI (g)
Is 794 at 25 °C. What is the value of K_eq for the equilibrium below?
1/2 H₂ (g) + 1/2 I₂ (g) HI (g)

A) 397
B) 0.035
C) 1588
D) 28
E) 0.0013

Question 53

Le Chatelier's principle states that if a system at equilibrium is disturbed, the equilibrium will shift to minimize the disturbance.

Question 54

At 200 °C, the equilibrium constant (K_p) for the reaction below is 2.40 × 10³.
2NO (g) N₂ (g) + O₂ (g)
A closed vessel is charged with 36.1 atm of NO. At equilibrium, the partial pressure of O₂ is
Atm)

A) 294
B) 6.00
C) 18.1
D) 35.7
E) 1.50 × 10^{- 2}

Question 55

A reaction vessel is charged with hydrogen iodide, which partially decomposes to molecular hydrogen and iodine:
2HI (g) H₂(g) + I₂(g)
^{When the system comes to equilibrium at 425 °C, P}_HI ^{= 0.708 atm, and P}H₂ ^{= P}I₂
= 0)0960 atm. The value of K_p at this temperature is .

A) 1.30 × 10^{- 2}
B) 6.80 × 10^{- 2}
C) K_p cannot be calculated for this gas reaction when the volume of the reaction vessel is not given.
D) 54.3
E) 1.84 × 10^{- 2}

Question 56

In the coal- gasification process, carbon monoxide is converted to carbon dioxide via the following reaction:
CO (g) + H₂O (g) CO₂ (g) + H₂ (g)
In an experiment, 0.35 mol of CO and 0.40 mol of H₂O were placed in a 1.00- L reaction vessel. At equilibrium, there were 0.19 mol of CO remaining. K_eq at the temperature of the experiment is
)

A) 0.56
B) 0.75
C) 1.78
D) 5.47
E) 1.0

Question 57

K_p = 0.0198 at 721 K for the reaction
2HI (g) H₂ (g) + I₂ (g)
In a particular experiment, the partial pressures of H₂ and I₂ at equilibrium are 0.710 and 0.888 atm, respectively. The partial pressure of HI is atm.

A) 7.87
B) 1.98
C) 0.125
D) 0.389
E) 5.64

Question 58

At constant temperature, reducing the volume of a gaseous equilibrium mixture causes the reaction to shift in the direction that increases the number of moles of gas in the system.