Question 1

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.

Accepted Answer

a. Partially. It is right that the system will be apparently unchanging to a casual inspection once equilibrium is attained. However, macroscopic observation cannot determine if reaction has proceeded "as far as it will go"-which implies that it has stopped. Infact, it has not.

b. No. The reaction (in both directions) wil be observed to continue. However the rates in the two directions are equal, which explains the macroscopic observation of Part a.

Question 2

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, Kc.

Accepted Answer

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

Question 3

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 ____.

Accepted Answer

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 C

Question 4

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

Accepted Answer

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 5

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

Accepted Answer

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

Question 6

If the value of Kc 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 ____.

Accepted Answer

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

Question 7

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

Accepted Answer

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 8

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

Accepted Answer

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

Question 9

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 Kc?

Accepted Answer

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

Question 10

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

Accepted Answer

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

Question 11

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

Accepted Answer

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 12

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

Accepted Answer

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 13

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

Accepted Answer

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 14

The concentration equilibrium constant, Kc, and the pressure equilibrium constant, Kp, are related by the expression

Accepted Answer

A)   Kc = Kp(RT) Dn
B)   Kc = Kp(Dn) RT
C)   Kp = Kc(RT) Dn
D)   Kp = Kc(R) TDn
E)   Kp = Kc(Dn) RT

Question 15

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

Accepted Answer

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

Question 16

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 Kp for this reaction at this temperature is

Accepted Answer

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

Question 17

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

Accepted Answer

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 18

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

Accepted Answer

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 19

The equilibrium constant expression for the reaction shown below is

Accepted Answer

A)   
B)   
C)   
D)   
E)

Question 20

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

Accepted Answer

A)   K = kreverse / kforward
B)   K = kforward / kreverse
C)   K = kforward × kreverse
D)   K = kforward
E)   K = kreverse

Exam 13: Chemical Equilibrium

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.

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.

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 .

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

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

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 .

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

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

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?

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:

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

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

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

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

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

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

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

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

The equilibrium constant expression for the reaction shown below is

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