Deck 13: Chemical Equilibrium

Question 1

The equilibrium constant expression for the reaction shown below is

A)
B)
C)
D)
E)

Answer 1

Question 2

Consider the equilibrium reaction In a particular experiment, the equilibrium concentration of N₂ is 0.048 M, of O₂, 0.093 M, and of N₂O, 6.55 × 10^-21 M. What is the value of the equilibrium constant K_c?

A) 1.5 × 10^-18
B) 2.0 × 10^-37
C) 2.2 × 10^-36
D) 3.1 × 10^-17
E) 5.0 × 10³⁶

Answer 2

2.0 × 10^-37

Question 3

Terms relating to certain types of substances are conventionally omitted from equilibrium constant expressions. These substances are

A) pure liquids and gases.
B) pure solids and liquids.
C) pure solids only.
D) pure liquids only.
E) pure solids, liquids and gases.

Answer 3

pure solids and liquids.

Question 4

Consider the gas-phase equilibrium A B. In a series of experiments, different initial amounts of A and B are mixed together, and the mixture in each case allowed to come to equilibrium. Which one of these experiments would yield values for the amounts of A and B present at equilibrium different from all the other experiments?

A) 3.0 moles A, 4.5 moles B
B) 4.5 moles A, 3.0 moles B
C) 1.5 moles A, 4.5 moles B
D) 7.5 moles A, no B
E) 0.5 moles A, 7.0 moles B

Question 5

The equilibrium constant expression for the reverse of the reaction given below is

A)
B)
C)
D)
E)

Question 6

A particular chemical reaction is

A) reactant-favored if the equilibrium constant is very large
B) product-favored if the equilibrium constant is very small
C) either product-favored or reactant-favored depending on the temperature of the reaction
D) either product-favored or reactant-favored depending on the pressure of the reaction
E) all of these

Question 7

The equilibrium constant for a reaction is related to the rate constants for the reaction as follows:

A) K = k_reverse / k_forward
B) K = k_forward / k_reverse
C) K = k_forward × k_reverse
D) K = k_forward
E) K = k_reverse

Question 8

Consider the gas-phase equilibrium A B. Certain amounts of A and B are mixed in a vessel. As they come to equilibrium

A) the forward reaction rate declines and the reverse reaction rate rises.
B) the reverse reaction rate declines and the forward reaction rate rises.
C) both forward and reverse reaction rates decline.
D) both forward and reverse reaction rates rise.
E) either a or b, but we cannot say which without more information.

Question 9

The equilibrium for a particular chemical reaction is dependent on the

A) homogeneous catalyst concentration, if catalyst is present
B) direction of approach
C) temperature of the reaction
D) atmospheric pressure
E) initial concentrations of the reactants

Question 10

The equilibrium constant for the reaction has a value of K_c = 1.23 at a certain temperature. What is the value of K_c for the reaction:

A) 2.46
B) 1.51
C) 0.66
D) 0.41
E) -1.51

Question 11

In a balanced chemical equation, if there is no net change in the total number of moles of gas from the reactant side to the product side, then

A) K_p = 1.00
B) K_p = K_c
C) K_c = 1.00
D) at equilibrium, the reaction has gone to 50% completion
E) all of these

Question 12

The concentration equilibrium constant, K_c, and the pressure equilibrium constant, K_p, are related by the expression

A) K_c = K_p(RT)^Dn
B) K_c = K_p(Dn)^RT
C) K_p = K_c(RT)^Dn
D) K_p = K_c(R)^TDn
E) K_p = K_c(Dn)^RT

Question 13

A weak acid is 5% ionized at equilibrium. Therefore we can say that the ionization reaction is ____-favored, because ____.

A) product; the amount of products << the amount of reactants
B) reactant; the amount of products << the amount of reactants
C) reactant; the amount of products >> the amount of reactants
D) product; the amount of products >> the amount of reactants
E) neither; not enough information is available to reach a conclusion

Question 14

Consider the equilibrium reaction A sample of pure NO₂(g) of concentration 0.140 M is allowed to come to equilibrium. It is then found that 57.0 % of the NO₂(g) has reacted to form N₂O₄(g). What is the value of K_c?

A) 0.211
B) 0.377
C) 0.754
D) 4.73
E) 11.0

Question 15

If the equilibrium constants for the two reactions and

are denoted K₁ and K₂ respectively, then the equilibrium constant for the reaction
equals

A) (K₁/K₂)².
B) (K₁K₂)².
C) K₁K₂.
D) K₁ + K₂.
E) K₁K₂/2.

Question 16

A chemical equilibrium may involve

A) reactants and products exhibiting different states of matter
B) molecular rearrangements
C) a chemical change of one compound into another
D) reaction of elements to produce one or more compounds
E) any of these

Question 17

The equilibrium constant for a particular chemical reaction is

A) dependent on the total pressure of the reaction
B) dependent on the temperature of the reaction
C) a numerical value between -¥ and +¥
D) unreliably determined if variable amounts of either solid or liquid reactants or products are present
E) both b and c

Question 18

If a catalyst is added to a chemical reaction, the equilibrium yield of a product will be ____, and the time taken to come to equilibrium will be ____ than before.

A) higher; less
B) lower; the same
C) higher; the same
D) the same; less
E) lower; less

Question 19

Which of the following is not true for equilibrium constants?

A) when related reactions are added together, their equilibrium constants are added together
B) the equilibrium constants of the forward and reverse reactions are negative reciprocals of one another
C) when the coefficients in a balanced chemical reaction are multiplied by a factor, the equilibrium constant is multiplied by the same factor
D) the equilibrium constants of the forward and reverse reactions are equal to the respective rate constants of these reactions
E) all of these

Question 20

A chemical reaction reaches equilibrium when

A) both the forward and reverse reactions stop
B) the forward and reverse reactions both occur at the same rate
C) all of the limiting reactant has been used up
D) all of the limiting reactant has been used up and all of the limiting product has been created
E) the actual yield of the reaction equals the theoretical yield

Question 21

Consider the equilibrium system If C is removed, the equilibrium will ____, and if CO is added, the equilibrium will ____.

A) shift to the left; shift to the left
B) shift to the right; shift to the right
C) shift to the right; shift to the left
D) be unchanged; shift to the left
E) be unchanged; shift to the right

Question 22

To decide whether a reaction mixture is at equilibrium, a student determines the value of Q, the reaction quotient, and finds that it is less than K. Therefore, the mixture is

A) at equilibrium, since there is as much reaction as required.
B) not at equilibrium, and will react to the right, to increase the amounts of products.
C) not at equilibrium, and will react to the left, to increase the amounts of reactants.
D) not at equilibrium, and will react to the right, to increase the amounts of reactants.
E) not at equilibrium, and will react to the left, to increase the amounts of products.

Question 23

An endothermic reaction which results in an increase in moles of gas will be most product-favored under conditions of ____ pressure and ____ temperature.

A) high; high
B) high; moderate
C) high; low
D) low; high
E) low; low

Question 24

Consider the reaction If the partial pressures in an equilibrium mixture of Br₂, Cl₂, and BrCl are 1.12 atm, 1.26 atm, and 3.14 atm, respectively, the value of K_p for this reaction at this temperature is

A) 6.99
B) 4.70
C) 1.91
D) 0.532
E) 0.142

Question 25

Consider the endothermic reaction If such a system at equilibrium is heated, equilibrium will ____, because ____.

A) be unchanged; temperature has no effect on equilibrium
B) shift to the left; increased temperature favors an exothermic reaction
C) shift to the right; increased temperature favors an exothermic reaction
D) shift to the right; increased temperature favors an endothermic reaction
E) shift to the left; increased temperature favors an endothermic reaction

Question 26

Which of the following is false?

A) a large equilibrium constant is indicative of a reactant-favored reaction
B) an equilibrium constant close to 1.00 always indicates a highly product-favored reaction
C) if K_p = K_c the reaction has gone to 100% completion at equilibrium
D) if K_p = K_c = 0.50, the reaction has gone to 50% completion at equilibrium
E) all of these

Question 27

For the reaction K_c = 1.4 × 10¹⁵. In an equilibrium mixture, [A] = 0.45 M. What is the concentration of B?

A) 2.8 × 10¹⁴
B) 0.90
C) 1.1 × 10¹⁵
D) 6.3 × 10¹⁴
E) 2.5 × 10⁷

Question 28

Consider the reaction If the partial pressures in an equilibrium mixture of H₂, Br₂, and HBr are 0.024 atm, 0.031 atm, and 5.07 atm, respectively, the value of K_p for this reaction at this temperature is

A) 3.5 × 10⁴
B) 1.4 × 10⁴
C) 6.8 × 10³
D) 3.7 × 10²
E) 1.9 × 10²

Question 29

For the reaction K_c = 0.95. A mixture of the three substances contains 0.45 M ethanol, 0.45 M acetic acid and 1.1 M ethyl acetate. Which statement is true?

A) Q < K, so the system will react left to right.
B) Q < K, so the system will react right to left.
C) The mixture is at equilibrium.
D) Q > K, so the system will react left to right.
E) Q > K, so the system will react right to left.

Question 30

If the reaction quotient, Q, is greater than the equilibrium constant, K, then

A) the forward reaction must be favored
B) the reaction will proceed in the forward direction
C) the reaction has gone to 100% completion and is at equilibrium
D) the reaction has not yet started in the forward direction
E) the reaction will proceed in the reverse direction

Question 31

For the reaction K_c = 1.37. If the concentrations of A and B are equal, what is the value of that concentration?

A) 0.685 M
B) 0.822 M
C) 1.17 M
D) 1.37 M
E) 1.88 M

Question 32

Once the reaction quotient, Q, has been determined for a reaction mixture, comparison with the value of the equilibrium constant, K, will determine

A) if the mixture is at equilibrium or not.
B) if the mixture has an excess of either products or reactants compared to equilibrium.
C) if the mixture will react to the left, to the right, or not at all.
D) Both a and b.
E) All of a, b, and c.

Question 33

For the reaction K_c = 168. A mixture contains some C(s), [CO] = 0.50 M and [CO₂] = 0.75 M. Therefore the system ____ at equilibrium, because ____.

A) is not; the value of Q is 0.67
B) is not; the value of Q is 1.5
C) is; the value of Q is 0.67
D) is not; the value of Q is 0.33
E) is; the value of Q is 0.33

Question 34

Consider the reaction If an equilibrium mixture of these three substances is compressed, equilibrium will ____, because ____.

A) shift to the right; higher pressure favors fewer moles of gas
B) shift top the right; higher pressure favors more moles of gas
C) shift to the left; higher pressure favors fewer moles of gas
D) shift to the left; higher pressure favors more moles of gas
E) be unchanged; solid NH₄Cl does not appear in the equilibrium constant expression.

Question 35

For the reaction K_c = 0.0600 at a certain temperature. In an equilibrium mixture of the three gases, [NH₃] = 0.242 M and [H₂] = 1.03 M. What is the concentration of N₂ in this system?

A) 3.9 M
B) 3.2 × 10^-3 M
C) 0.89 M
D) 1.4 × 10^-2 M
E) 3.7 M

Question 36

Consider the equilibrium system If more C(s) is added, the equilibrium will ____; if CO is removed the equilibrium will ____.

A) shift to the left; shift to the left
B) shift to the right; shift to the right
C) shift to the right; shift to the left
D) be unchanged; shift to the left
E) be unchanged; shift to the right

Question 37

A particular reaction mixture (K_p = 10) consisting of both gaseous reactants and products is analyzed and is determined to have a value of Q = 15. The pressure of the reaction mixture is then doubled by the addition of argon gas and the reaction is allowed to proceed to equilibrium. At equilibrium

A) K_p > 10
B) Q = 15
C) Q = 10
D) K_p < 10
E) Q = 30

Question 38

Consider the reaction At equilibrium, [CO] = 4.14 × 10^-6 M; [Cl₂] = 4.14 × 10^-6 M; and [COCl₂] = 0.0627 M. Calculate the value of the equilibrium constant, K_c.

A) 2.73 × 10^-10
B) 6.60 × 10^-5
C) 1.32 × 10^-4
D) 1.51 × 10⁴
E) 3.66 × 10⁹

Question 39

Consider the reaction If the pressure is decreased on an equilibrium mixture of these three substances, equilibrium will ____, because ____.

A) shift to the right; lower pressure favors fewer moles of gas
B) shift to the right; lower pressure favors more moles of gas
C) shift to the left; lower pressure favors fewer moles of gas
D) shift to the left; lower pressure favors more moles of gas
E) be unchanged; solid NH₄Cl does not appear in the equilibrium constant expression.

Question 40

Consider the exothermic reaction at equilibrium: If the system is cooled, the equilibrium will ____, because ____.

A) be unchanged; temperature has no effect on equilibrium
B) shift to the left; decreased temperature favors an exothermic reaction
C) shift to the right; decreased temperature favors an exothermic reaction
D) shift to the right; decreased temperature favors an endothermic reaction
E) shift to the left; decreased temperature favors an endothermic reaction

Question 41

If the value of K_c for a given reaction at a given temperature is a large number, the energy of the products is likely to be ____ the energy of the reactants because ____.

A) greater than; the value of K_c favors the reactants
B) less than; the value of K_c favors the reactants
C) the same as; the value of K_c favors neither the products nor the reactants
D) greater than; the value of K_c favors the products
E) less than; the value of K_c favors the products

Question 42

This reaction is the basis for the Haber-Bosch process for the manufacture of ammonia: To maximize the yield of ammonia, the pressure ____ and the temperature____.

A) should be kept high by compressing the mixture; should be kept low
B) should be kept high by compressing the mixture; should be kept high
C) should be kept high by adding an inert gas; should be kept low
D) should be kept high by adding an inert gas; should be kept high
E) should be kept low; should be kept low

Question 43

The reaction
is the basis of a very ancient chemical industry. Seashells or chalk (limestone) are roasted in kilns to produce CaO (quicklime). When moistened and used in a mortar, this forms Ca(OH)₂ (slaked lime). Atmospheric CO₂ slowly converts this back to CaCO₃. A strong bond thus results between the stones used in the wall.
a. Is the above reaction exothermic or endothermic? Explain.
b. Lime kilns, since ancient times, have been designed with efficient chimneys to draw exhaust gases away. In terms of Le Chatelier's Principle, give two reasons why this enhances the conversion of limestone to quicklime.
c. When a sample of CaCO₃(s) is placed in a sealed, evacuated container, the equilibrium CO₂ pressure at a given temperature is always the same, and is not influenced by the amount of CaCO₃, provided that there is still some present at equilibrium. Explain why.
d. How would the result in Part c be affected by adding an equal number of moles of CaO to the flask? Explain.

Question 44

For an exothermic reaction, an increase in temperature

A) always means an increase in K_c
B) always means a decrease in K_c
C) the reaction will become more product-favored at higher temperatures
D) the reaction will become more reactant-favored at higher temperatures
E) both b and d

Question 45

If a reaction is product-favored on the basis of enthalpy and reactant-favored on the basis of entropy, then it most likely is ____ and ____ net moles of gas.

A) exothermic; produces
B) exothermic; consumes
C) exothermic; neither produces nor consumes
D) endothermic; produces
E) endothermic; consumes

Question 46

Consider the reaction
for which K_p = 2.00 at 20 ^$\circ$ C. A mixture of NO(g) at a partial pressure of 1.50 atm and NO₂(g) at a partial pressure of 0.50 atm is allowed to come to equilibrium in a sealed container maintained at 20 ^$\circ$ C. What is the total pressure now?
The expression for
.

Question 47

Which statement concerning product-favored reactions is not correct?

A) If a reaction is product-favored at high temperature, the entropy of the products is probably greater than the entropy of the reactants.
B) If a reaction is product-favored at low temperature, the enthalpy of the products is probably less than the enthalpy of the reactants.
C) If the entropy of the products is greater than the entropy of the reactants, the reaction is product-favored.
D) An endothermic reaction is product-favored.
E) The value of the equilibrium constant is greater than 1.

Question 48

Which of the following is true for an equilibrium system?

A) in an equilibrium system, molecules that are higher in energy occur less often
B) if there are more product molecules than reactant molecules, entropy favors the products in an equilibrium system
C) the higher the temperature is, the less important the energy effect (DH) becomes
D) the higher the temperature is, the more the entropy effect (dispersal of energy) determines the position of equilibrium
E) all of these

Question 49

Consider the statement, "At equilibrium, a reaction has proceeded as far as it will go, and no further reaction will be observed."
a. From a macroscopic viewpoint, is this statement correct ? Explain your answer.
b. From a nanoscale viewpoint, is this statement correct? Explain your answer.

Question 50

In predicting which side of an equilibrium is more favored, the factor concerned with probability is called

A) enthalpy.
B) endoscopy.
C) endothermic.
D) entropy.
E) exothermic.

Question 51

Consider the reaction
for which
.
A sample of pure NOBr is isolated at low temperature. It is placed in a flask at a concentration of 0.200 M and warmed up to 50 ^$\circ$ C. When the reaction has come to equilibrium, the concentration of NOBr is 0.176 M. What is the value of K_c at 50 ^$\circ$ C for this reaction?

Question 52

For a particular chemical reaction, which of the following will result in a change of the equilibrium constant?

A) a change in pressure
B) a change in the temperature
C) adding additional reactant
D) removing product
E) the equilibrium constant never changes

Question 53

Considering only the probability factor in the gas-phase reaction C 2 A + B, ____ side is favored because ____.

A) the product; there are more possible arrangements of molecules on the reactant side
B) the product; there are more possible arrangements of molecules on the product side
C) the reactant; there are more possible arrangements of molecules on the reactant side
D) the reactant; there are more possible arrangements of molecules on the product side
E) one cannot say which; more information is needed.

Question 54

Consider the reaction Consider an equilibrium mixture of these substances. If the pressure is increased by compressing the mixture, equilibrium will ____; if pressure is increased by adding an inert gas to the mixture, equilibrium will ____.

A) shift to the left; shift to the left
B) shift to the right; shift to the left
C) shift to the left; remain unchanged
D) shift to the right; remain unchanged
E) shift to the right; shift to the right

Question 55

As the temperature is increased, which kinds of reactions become more product-favored?

A) Only those that are endothermic and result in an increase in entropy.
B) Only those that are exothermic and result in an increase in entropy.
C) All reactions that result in an increase in entropy.
D) All reactions that result in an decrease in entropy.
E) Only those that are exothermic and result in an decrease in entropy.

Question 56

If the value of K_c for a given reaction at a given temperature is a small number, the energy of the products is likely to be ____ the energy of the reactants because ____.

A) greater than; the value of K_c favors the reactants
B) less than; the value of K_c favors the reactants
C) the same as; the value of K_c favors neither the products nor the reactants
D) greater than; the value of K_c favors the products
E) less than; the value of K_c favors the products

Question 57

Concerning the Haber-Bosch for the synthesis of ammonia, which of the following is true?

A) the reaction is strongly exothermic
B) the reaction is carried out at high pressure
C) ammonia is continually liquefied and removed from the process
D) the temperature is raised because the reaction is too slow at room temperature
E) all of these