Deck 6: Chemical Equilibrium

Question 1

A system at a state of chemical equilibrium is

A) microscopically dynamic and macroscopically dynamic.
B) microscopically dynamic and macroscopically static.
C) microscopically static and macroscopically static.
D) microscopically static and macroscopically dynamic.
E) none of these

Answer 1

microscopically dynamic and macroscopically static.

Question 2

The value of the equilibrium constant K is dependent on:
I.The temperature of the system.
II.The nature of the reactants and products.
III.The concentration of the reactants.
IV.The concentration of the products.

A) I and II only
B) III and IV only
C) II and III only
D) three of these
E) none of these

Answer 2

I and II only

Question 3

The value of K_p for the reaction H₂(g) + O₂(g) H₂O₂(g) is 2.3 *10⁶ at 570K. Determine the value for K for this reaction at 570K.

A) 1.1 * 10¹⁰
B) 4.9 *10⁴
C) 1.1 * 10⁸
D) 2.3 * 10⁶
E) 4.3*10^-7

Answer 3

1.1 * 10⁸

Question 4

At -80°C, K for the reaction N₂O₄(g) 2NO₂(g)
Is 4.66 *10^-8. We introduce 0.034 mol of N₂O₄ into a 2.5-L vessel at -80°C and let equilibrium be established. The total pressure in the system at equilibrium will be

A) 4.66 *10^-8 atm.
B) 0.22 atm.
C) 0.09 atm.
D) 0.43 atm.
E) 0.23 atm.

Question 5

Consider the reaction CaCl₂(s) + 2H₂O(g) CaCl₂•2H₂O(s)
What is the equilibrium constant for the reaction as written?

A) K = [H₂O]²
B) K =
C) K =
D) K =
E) K =

Question 6

The equilibrium constant for A + 2B 3C is 1.0 * 10^-6. Determine the equilibrium constant for 4A + 8B 11eff479_2c3f_bf8d_9103_65e4a477b15e_TB6420_00 12C.

A) 1.0 *10^-24
B) 1.0 * 10²⁴
C) 1.0* 10^-6
D) 4 * 10^-24
E) 4 *10^-6

Question 7

Choose the mass action or equilibrium expression for the reaction 2SO₂(g) + O₂(g) 2SO₃(g)

A)
B)
C)
D)
E) none of these

Question 8

Which of the following is an example of a homogeneous equilibrium?

A) CaCl₂(s) + 2H₂O(g) CaCl₂•2H₂O(s)
B) H₂(g) + I₂(s) 2HI(g)
C) NH₄NO₃(s) N₂O(g) + 2H₂O(g)
D) 2N₂O(g) + N₂H₄(g) 3N₂(g) + 2H₂O(g)
E) none of these

Question 9

If, at a given temperature, the equilibrium constant for the reaction H₂(g) + Cl₂(g) 2HCl(g) is 4.2, then the equilibrium constant for the reaction HCl(g) (1/2)H₂(g) + (1/2)Cl₂(g) can be represented as

A) 0.057.
B)18.
C) 0.49.
D) 0.24.
E) 4.2.

Question 10

Indicate the mass action expression for the following reaction: 2X(g) + Y(g) 3W(g) + V(g)

A)

B)

C) [X]²[Y][W]³[V]

D)

Question 11

For the reaction 2NCl₃(g) N₂(g) + 3Cl₂(g), the equilibrium pressures are P(NCl₃) = 0.134 atm
P(N₂) = 2.31 atm
P(Cl₂) = 0.0510 atm
Determine K_p for this reaction.

A) 0.0171
B) 58.6
C) 9.19
D) 1.32
E) 0.879

Question 12

Consider the following equilibrium: Which of the following is the proper K_eq expression?

A)
B)
C)
D)
E)

Question 13

The reaction H₂(g) + I₂(g) 2HI(g)
Has K_p = 45.9 at 763 K. A particular equilibrium mixture at that temperature contains gaseous HI at a partial pressure of 4.30 atm and hydrogen gas at a partial pressure of 0.225 atm. What is the partial pressure of I₂?

A) 1.79 atm
B) 0.225 atm
C) 0.833 atm
D) 37.1 atm
E) 0.416 atm

Question 14

For the hypothetical reactions 1 and 2, K₁ = 10² and K₂ = 10^-4. 1. A₂(g) + B₂(g) 2AB(g)
2) 2A₂(g) + C₂(g) 2A₂C(g)
3) A₂C(g) + B₂(g) 2AB(g) + (1/2)C₂(g)
What is the value for K for reaction 3?

A) 10^-2
B) 10⁴
C) 10⁶
D) 10²
E) 10^-4

Question 15

For the reaction 2H₂(g) + O₂(g) 2H₂O(g), what is the relationship between K and K_p at temperature T?

A) K_p = K(RT)²
B) K = K_p(RT)
C) K = K_p
D) K_p = K(RT)
E) K = K_p(RT)²

Question 16

Consider the equation 2NOCl₂(g) 2NO(g) + Cl₂(g). The equilibrium constant is 0.0132 at 119°C. Calculate K_p.

A) 0.0132
B) 0.129
C) 0.425
D) 4.10* 10^-4
E) 43.0

Question 17

For the reaction below, K_p = 1.16 at 700.°C. CaCO₃(s) CaO(s) + CO₂(g)
If a 24.6-g sample of CaCO₃ is put into a 14.2-L container and heated to 700.°C, what percent of the CaCO₃ will react to reach equilibrium?

A) 20.6%
B) 36.9%
C) 83.9%
D)100.%
E) 67.0%

Question 18

Which of the following statements concerning equilibrium is not true?

A) A system that is disturbed from an equilibrium condition responds in such a way as to restore equilibrium.
B) The value of the equilibrium constant for a given reaction mixture is the same regardless of the direction from which equilibrium is attained.
C) Equilibrium in molecular systems is dynamic, with two opposing processes balancing one another.
D) The equilibrium constant is independent of temperature.
E) A system moves spontaneously toward a state of equilibrium.

Question 19

Which of the following statements is true?

A) When two opposing processes are proceeding at identical rates, the system is at equilibrium.
B) An endothermic reaction shifts toward reactants when heat is added to the reaction.
C) The concentration of the products equals that of the reactants and is constant at equilibrium.
D) Catalysts are an effective means of changing the position of an equilibrium.
E) None of the above statements is true.

Question 20

The value of the equilibrium constant K depends on:
I.The initial concentrations of the reactants.
II.The initial concentrations of the products.
III.The final concentrations of the reactants.
IV.The final concentrations of the products.

A) II and III only
B) III and IV only
C) I and II only
D) three of these
E) none of these

Question 21

Consider the equation 2A(g) 2B(g) + C(g). At a particular temperature, K = 1.6 *10⁴. If you start with 2.0 M of chemical A, calculate the equilibrium concentration of chemical C.

A) 8.3 *10^-3 M
B) 1.6 *10^-2 M
C) 6.25 *10^-5 M
D) 2.0 M
E) 0.98 M

Question 22

Nitric oxide, an important pollutant in air, is formed from the elements nitrogen and oxygen at high temperatures, such as those obtained when gasoline burns in an automobile engine. At 2000°C, K for the reaction N₂(g) + O₂(g) 2NO(g) is 0.01. Predict the direction in which the system will move to reach equilibrium at 2000°C if 0.4 mol of N₂, 0.1 mol of O₂, and 0.08 mol of NO are placed in a 1.0-L container.

A) The system remains unchanged.
B) The concentration of NO will decrease; the concentrations of N₂ and O₂ will remain unchanged.
C) The concentration of NO will decrease; the concentrations of N₂ and O₂ will increase.
D) The concentration of NO will increase; the concentrations of N₂ and O₂ will decrease.
E) More information is necessary.

Question 23

Consider the following equilibrium: N₂(g) + 3H₂(g) 2NH₃(g)
With K = 2.3 *10^-6. 1.00 mol each of all reactants and products is placed in a 1.00-L container.
Which way will the reaction initially proceed?

A) To the right.
B) We need to know the temperature.
C) The system is at equilibrium.
D) To the left.
E) none of these

Question 24

Consider the equation 2A(g) 2B(g) + C(g). At a particular temperature, K = 1.6 * 10⁴. At a higher temperature, K = 1.8 * 10^-5. If you start with 2.0 M of chemical A, calculate the equilibrium concentration of chemical C.

A) 2.6 *10^-2 M
B) 6.0 * 10^-3 M
C) 1.0 M
D) 2.1 *10^-2 M
E) none of these

Question 25

Consider the following reaction: 2NOCl(g) 2NO(g) + Cl₂(g)
Initially pure NOCl(g) is placed in a vessel at 2.97 atm. At equilibrium, 0.416% of the NOCl has decomposed. Determine the value for K_p.

A) 5.16*10^-5
B) 2.70 * 10^-8
C) 6.18 * 10^-3
D) 1.08 * 10^-7
E) 2.16 * 10^-7

Question 26

Consider the following reaction: 2HF(g) H₂(g) + F₂(g) (K = 1.00 *10^-2)
Given 1.22 mol of HF(g), 0.760 mol of H₂(g), and 1.09 mol of F₂(g) are mixed in a 4.00-L flask, determine the reaction quotient, Q, and the net direction to achieve equilibrium.

A) Q = 0.557; the equilibrium shifts to the right.
B) Q = 0.679; the equilibrium shifts to the left.
C) Q = 0.679; the equilibrium shifts to the right.
D) Q = 0.557; the equilibrium shifts to the left.
E) Q = 1.43; the system is at equilibrium.

Question 27

Consider the reaction 2SO₂(g) + O₂(g) 2SO₃(g)
At constant temperature. Initially a container is filled with pure SO₃(g) at a pressure of 2 atm, after which equilibrium is allowed to be reached. If y is the partial pressure of O₂ at equilibrium, what is the value of K_p?

A)
B)
C)
D)
E) none of these

Question 28

Consider the equation 2A(g) 2B(g) + C(g). At a particular temperature, K = 1.6 *10⁴. If you mixed 5.0 mol B, 0.10 mol C, and 0.0010 mol A in a 1-L container, in which direction would the reaction initially proceed?

A) To the right.
B) To the left.
C) The above mixture is the equilibrium mixture.
D) We cannot tell from the information given.

Question 29

What is the equilibrium expression for the following reaction? NH₄NO₃(s) N₂O(g) + 2H₂O(g)

A)
B)
C)
D) [N₂O][H₂O]²
E) none of these

Question 30

Consider the following reaction (assume an ideal gas mixture). 2NOBr(g) 2NO(g) + Br₂(g)
A 3)0-L vessel was initially filled with pure NOBr, at a pressure of 4.0 atm, at 300 K.
After equilibrium was established, the partial pressure of NOBr was 2.1 atm. What is K_p for the reaction?

A) 0.78
B) 0.26
C) 1.56
D) 1.72
E) 1.1

Question 31

Consider the following equilibrium:
N₂(g) + 3H₂(g) 2NH₃(g)
with K = 2.3 *10^-6. 1.00 mol each of all reactants and products is placed in a 1.00-L container.

-Calculate the equilibrium concentration of N₂.

A) 1.5 M
B) 2.0 M
C) 0.5 M
D) 2.5 M
E) 1.0 M

Question 32

Consider the decomposition of hydrazine as shown below. N₂H₄(g) 2H₂(g) + N₂(g)
At a certain temperature, K_p = 2.5 *10³. When pure hydrazine is placed in an otherwise empty vessel at this temperature, equilibrium is reached after 30.0% of the hydrazine has decomposed. Calculate the partial pressure of hydrogen gas at equilibrium.

A) 76 atm
B) 5776 atm
C) 54 atm
D) 127 atm
E) none of these

Question 33

Nitric oxide, an important pollutant in air, is formed from the elements nitrogen and oxygen at high temperatures, such as those obtained when gasoline burns in an automobile engine. At 2000°C, K for the reaction N₂(g) + O₂(g) 2NO(g) is 0.01. A 1-L container originally holds 0.4 mol of N₂, 0.1 mol of O₂, and 0.08 mol of NO. If the volume of the container holding the equilibrium mixture of N₂, O₂, and NO is decreased to 0.5 L without changing the quantities of the gases present, how will their concentrations change?

A) The concentrations of N₂ and O₂ will increase, and the concentration of NO will decrease.
B) The concentrations of N₂, O₂, and NO will decrease.
C) The concentrations of N₂, O₂, and NO will increase.
D) There will be no change in the concentrations of N₂, O₂, and NO.
E) The concentration of NO will increase, and the concentrations of N₂ and O₂ will decrease.

Question 34

A sample of solid NH₄NO₃ was placed in an evacuated container and then heated so that it decomposed explosively according to the following reaction: NH₄NO₃(s) N₂O(g) + 2H₂O(g)
At equilibrium, the total pressure in the container was found to be 2.25 atm at a temperature of 500°C. Calculate K_p.

A) 2.25.
B) 5.06
C) 45.6
D) 1.69
E) 2.25

Question 35

Consider the reaction 2NOBr(g) 2NO(g) + Br₂(g)
A 1)0-L vessel was initially filled with pure NOBr at a pressure of 3.8 atm and 300 K. At equilibrium, the partial pressure of NOBr was 2.0 atm. Determine the value of K_p for the reaction.

A) 1.6
B) 1.4
C) 0.81
D) 0.73
E) 0.90

Question 36

At a certain temperature, K for the reaction 2NO₂ N₂O₄
Is 7.5 L/mol. If 2.0 mol of NO₂ is placed in a 2.0-liter container and permitted to react at this temperature, calculate the concentration of N₂O₄ at equilibrium.

A) 0.39 mol/L
B) 0.82 mol/L
C) 7.5 mol/L
D) 0.65 mol/L
E) none of these

Question 37

For a particular system at a particular temperature, there are ______ equilibrium constant(s) and _______ equilibrium position(s).

A) one, one
B) one, an infinite number of
C) an infinite number of, one
D) an infinite number of, an infinite number of
E) none of these

Question 38

Consider the following equilibrium:
N₂(g) + 3H₂(g) 2NH₃(g)
with K = 2.3 *10^-6. 1.00 mol each of all reactants and products is placed in a 1.00-L container.

-Calculate the equilibrium concentration of H₂.

A) 0.5 M
B) 1.0 M
C) 2.5 M
D) 2.0 M
E) 1.5 M

Question 39

At a given temperature, the equilibrium constant K for the reaction 2SO₂(g) + O₂(g) 2SO₃(g)
Is 3.0 *10⁹. If 2.60 mol of SO₂ and 3.90 mol of O₂ are placed in a 1.78-L container and allowed to react to equilibrium at this temperature, what is the concentration of SO₃ at equilibrium?

A) 1.46 M
B) 0.730 M
C) 2.92 M
D) 3.65 M
E) 2.19 M

Question 40

The following reaction is investigated (assume an ideal gas mixture). 2N₂O(g) + N₂H₄(g) 3N₂(g) + 2H₂O(g)
Initially there are 0.08 mol of N₂O and 0.29 mol of N₂H₄, in a 20.0-L container. If there is 0.050 mol of N₂O at equilibrium, how many moles of N₂ are present at equilibrium?

A) 0.053
B) 0.045
C) 0.12
D) 0.030
E) 0.15

Question 41

Consider the following reaction (assume an ideal gas mixture). 2NOBr(g) 2NO(g) + Br₂(g)
A 3)0-L vessel was initially filled with pure NOBr, at a pressure of 3.7 atm, at 290 K.
After equilibrium was reached, the volume was increased to 2.0 L, while the temperature was kept at 300 K. This will result in

A) a decrease in K_p.
B) a shift in the equilibrium position to the right.
C) an increase in K_p.
D) a shift in the equilibrium position to the left.
E) none of these

Question 42

Consider the equation 2A(g) 2B(g) + C(g). At a particular temperature, K = 1.6 * 10⁴.

-Addition of chemical B to an equilibrium mixture of the above will

A) cause [A] to increase.
B) have no effect.
C) cause [C] to increase.
D) cannot be determined
E) none of these

Question 43

To increase the value of K for the exothermic reaction 2H₂(g) + O₂(g) H₂O(g)
We should

A) decrease the temperature.
B) decrease the total pressure.
C) increase the total pressure.
D) increase the temperature.
E) Two of these are necessary.

Question 44

Consider the following reaction:
How can the equilibrium be shifted to the right?

A) Remove Cl₂.
B) Decrease the pressure by changing the volume.
C) Remove PCl₃.
D) Add more PCl₅.
E) Any of these will shift the equilibrium to the right.

Question 45

Explain how chemical equilibrium is microscopically dynamic and macroscopically static.

Question 46

Derive the relationship between K and K_p.

Question 47

Given the reaction A(g) + B(g) C(g) + D(g). You have the gases A, B, C, and D at equilibrium. Upon adding gas A, the value of K

A) depends on whether the reaction is endothermic or exothermic.
B) does not change as long as the temperature is constant.
C) does not change because A does not figure in the ratio of product to reactant.
D) decreases because A is a reactant, so the ratio of product to reactant decreases.
E) increases because when A is added, more products are made, increasing the ratio of product to reactant.

Question 48

Nitrogen gas (N₂) reacts with hydrogen gas (H₂) to form ammonia (NH₃). At 200°C in a closed container, 1.0 atm of nitrogen gas is mixed with 2.1 atm of hydrogen gas. At equilibrium, the total pressure is 2.1 atm. Calculate the partial pressure of hydrogen gas at equilibrium.

A) 2.1 atm
B) 0.0 atm
C) 1.8 atm
D) 0.60 atm
E) 0.65 atm

Question 49

Ammonia is prepared industrially by the following reaction: N₂(g) + 3H₂(g) 2NH₃(g)
For the reaction, $\Delta$ H° = -92.2 kJ and K (at 25°C) = 4.0 *10⁸. When the temperature of the reaction is increased to 500°C, which of the following statements is true?

A) Product formation (at equilibrium) is not favored as the temperature is raised.
B) K for the reaction will be larger at 500°C than at 25°C.
C) The reaction of N₂ with H₂ to form ammonia is endothermic.
D) At equilibrium, more NH₃ is present at 500°C than at 25°C.
E) None of these is true.

Question 50

Consider the following reaction:
Which of the following statements is false?

A) Decreasing the volume of the container shifts the equilibrium to form more PCl₅.
B) Removing PCl₅ from the container shifts the equilibrium to form more PCl₃.
C) Adding PCl₃ to the container shifts the equilibrium to form more PCl₅.
D) Increasing the temperature shifts the equilibrium to form more PCl₃.

Question 51

Consider the equation A(aq) + 2B(aq) 3C(aq) + 2D(aq). 42.0 mL of 0.046 M A is mixed with 24.0 mL 0.105 M B. At equilibrium, the concentration of C is 0.0416 M. Calculate K.

A) 0.074
B) 4.8
C) 0.0029
D) 2.9 *10^-4
E) 0.033

Question 52

When the substances in the equation below are at equilibrium at pressure P and temperature T, how can the equilibrium be shifted to favor the products? CuO(s) + H₂(g) Cu(s) + H₂O(g)
Change in enthalpy = -2.0 kJ.

A) Increase the pressure by adding an inert gas such as nitrogen.
B) Allow some gas to escape at constant pressure and temperature.
C) Decrease the temperature.
D) Increase the pressure by means of a moving piston at constant temperature.
E) Add a catalyst.

Question 53

Consider the following equilibrium: Which of the following statements about the equilibrium is false?

A) Removing HI as it forms forces the equilibrium to the right.
B) Adding more H₂(g) increases the equilibrium constant.
C) This is a heterogeneous equilibrium.
D) If the pressure on the system is increased by changing the volume, the left side is favored.
E) If the system is heated, the right side is favored.

Question 54

Consider the following reaction:
Which of the following statements is true?

A) Increasing the temperature of a system at equilibrium always increases the amount of product.
B) Increasing the temperature of a system at equilibrium changes the value of the equilibrium constant.
C) Increasing the temperature of a system at equilibrium always decreases the amount of product.
D) Changing the temperature of a system at equilibrium does not affect the equilibrium position.
E) none of these

Question 55

Consider the equation 2A(g) 2B(g) + C(g). At a particular temperature, K = 1.6 * 10⁴.

-Raising the pressure by lowering the volume of the container will

A) cause [B] to increase.
B) have no effect.
C) cause [A] to increase.
D) cannot be determined
E) none of the these

Question 56

Explain how a given system at a given temperature has one equilibrium constant but an infinite number of equilibrium positions.

Question 57

Consider the following equilibrium:
N₂(g) + 3H₂(g) 2NH₃(g)
with K = 2.3 *10^-6. 1.00 mol each of all reactants and products is placed in a 1.00-L container.

-Calculate the equilibrium concentration of NH₃(g).

A) 3.7 * 10^-3 M
B) 5.4 * 10^-5 M
C) 7.3 * 10^-3 M
D) 4.3 *10^-6 M
E) none of these

Question 58

For a certain reaction at 25.0°C, the value of K is 1.2 * 10^-3. At 50.0°C the value of K is 3.4 *10^-1. This means that the reaction is

A) endothermic
B) exothermic
C) We need more information.

Question 59

Consider the equation 2A(g) 2B(g) + C(g). At a particular temperature, K = 1.6 *10⁴. Placing the equilibrium mixture in an ice bath (thus lowering the temperature) will

A) have no effect.
B) cause [A] to increase.
C) cause [B] to increase.
D) cannot be determined
E) none of these

Question 60

Write the equilibrium constant expression for the following reaction:
CaCO₃(s) CaO(s) + CO₂(g)

Question 61

At equilibrium, the partial pressure of HCl will be

A) impossible to determine with this information
B) less than 2 atm
C) zero
D) between 2 and 4 atm
E) more than 4 atm

Question 62

Once equilibrium was established, some additional chlorine gas was added to the system. This resulted in

A) no net change in the amounts of the other reaction components.
B) an increase in the amount of H₂O relative to the equilibrium mixture.
C) a decrease in the amount of H₂O relative to the equilibrium mixture.
D) a decrease in the amount of HCl relative to the equilibrium mixture.
E) both B and D

Question 63

At 25° C a sample of N₂O₄(g) is placed in an empty cylinder. After equilibrium is reached, the total pressure is 1.5 atm, and 16% (by moles) of the original N₂O₄ has dissociated to NO₂(g). If the volume of the cylinder is increased until the total pressure is 1.0 atm, what percent (by moles) of the original N₂O₄(g) has dissociated at the new equilibrium position? (Hint: First calculate K_p.)

Question 64

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) 2.3
C) 0.23
D) 0.43
E) 0.77

Question 65

State Le Châtelier's principle.

Question 66

To achieve equilibrium, the original reaction mixture will

A) produce more water and oxygen only
B) experience no change in component pressures
C) always move in a direction to lower the total pressure
D) shift toward products
E) shift toward reactants

Question 67

What is the value of Q₀, the reaction quotient, based on the conditions above?

A) 0.50
B) 0.125
C) 4.00
D) 1.00
E) None of the above

Question 68

In the reaction
P₄(g) 2P₂(g)
K_p = 0.500 atm at 1052°C. In an experiment, P₄(g) is initially placed into a container at 1052°C. The total pressure of the equilibrium mixture of P₄(g) and P₂(g) is 6.00 atm. Calculate the equilibrium pressures of P₄(g) and P₂(g). Calculate the fraction (by moles) of P₄(g) that has dissociated to reach equilibrium.

Question 69

What is the partial pressure of O₂ at equilibrium?

A) 2.18 atm
B) 0.91 atm
C) 1.64 atm
D) 1.18 atm
E) 2.27 atm
F) none of the above

Question 70

Consider the following reaction, which is involved in the catalytic destruction of ozone by chlorine atoms.
ClO(g) + O₃(g) Cl(g) + 2O₂(g)
K_p = 2.5 * 10⁶ atm at 25° C. In an experiment at 25° C, ClO(g) at 1.0 *10^-3 atm was mixed with O₃(g) at 2.0 *10^-5 atm in a rigid vessel. Calculate the equilibrium pressure of O₃(g) and O₂(g).

Question 71

A mixture of O₂(g) and O₃(g) is present at equilibrium in a rigid container at 152 torr and 125° C. The density of the gaseous mixture is 0.228 g/L. Calculate K_p at 125° C for the reaction
3O₂(g) 2O₃(g)