Deck 16: Reaction Rates and Chemical Equilibrium

Question 1

Most reactions are carried out in liquid solution or in the gaseous phase because in such situations ________.

A) activation energies are higher
B) reactant activation energies are lower
C) kinetic energies of reactants are lower
D) reactant collisions occur more frequently

Answer 1

reactant collisions occur more frequently

Question 2

For a collision between molecules to result in reaction, the molecules must possess a favorable orientation relative to each other ________.

A) and exchange electrons
B) and "stick together" for at least 10 seconds
C) and a certain minimum energy
D) and be in the gaseous state

Answer 2

and a certain minimum energy

Question 3

Whether a reaction is exothermic or endothermic is determined by ________.

A) the activation energy
B) the physical state of the reaction system
C) energy balance between bond breaking and bond forming resulting in a net loss or gain of energy
D) whether a catalyst is present

Answer 3

energy balance between bond breaking and bond forming resulting in a net loss or gain of energy

Question 4

Which reaction below is endothermic?

A) NH₃ + HBr $\rightarrow$ NH₄Br + heat
B) CH₄ + N₂ + heat $\rightarrow$ HCN + NH₃
C) 2NO₂ $\rightarrow$ N₂ + 2O₂ + heat
D) PCl₃ + Cl₂ $\rightarrow$ PCl₅ + heat

Question 5

A catalyst works by:

A) increasing the rate of a reaction by decreasing the heat of reaction
B) increasing the rate of a reaction by lowering the activation energy of the forward reaction only
C) increasing the rate of a reaction by increasing the activation energy of the reverse reaction only
D) increasing the rate of a reaction by providing an alternative pathway with a lower activation energy

Question 6

Which of the following changes would most likely decrease the rate of a reaction?

A) increasing the activation energy for the reaction
B) decreasing the activation energy for the reaction
C) increasing the reaction temperature
D) increasing the concentration of a reactant

Question 7

Catalysts are correctly characterized by each of the following statements except one. The exception is ________.

A) catalysts can be either solids, liquids or gases
B) catalysts lower the activation energy for a reaction
C) catalysts do not "actively" participate in a reaction
D) catalysts are not "consumed" in a reaction

Question 8

Reaction A releases 24 kJ/mole and has an activation energy of 98 kJ/mole. Which statement is correct concerning Reaction A?

A) The overall reaction is endothermic with a high activation energy.
B) The overall reaction is endothermic with a low activation energy.
C) The overall reaction is exothermic with a high activation energy.
D) The overall reaction is exothermic with a low activation energy.

Question 9

Reaction conditions for a hypothetical reaction, X + Y $\rightarrow$ W + Z, are given below. Predict which reaction should occur at a faster rate. (M = molarity)Activation

A) 1
B) 2
C) 3
D) 4

Question 10

Which response includes all the factors that would increase the rate of a chemical reaction, and no others?
I. Lowering the temperature of the chemical reaction.
II. Significantly increasing the concentration of one of the reactants.
III. Adding a catalyst to an uncatalyzed reaction.
IV. Decrease the reaction surface area.
V. Increasing the pressure on a gaseous reaction system.

A) I and IV
B) II, III and V
C) I, IV and V
D) III only

Question 11

Increasing the temperature of a chemical reaction increases the rate of reaction because ________.

A) the activation energy decreases
B) the activation energy increases
C) the collision frequency of reactant molecules increases
D) both the collision frequency and collision energies of reactant molecules increases

Question 12

At equilibrium, the equilibrium constant for the following hypothetical reaction is two (K_eq = 2), [A] = 4, [B] = 8, and [AB] = 16 at 25 °C. AB + Heat $\rightarrow$ A (g) + B (g)
After a stress has been absorbed by the reaction, the new equilibrium concentrations are: [A] = 2, [B] = 1, and [AB] = 64. The stress absorbed by the equilibrium system ________.

A) was a change in the reaction temperature evident by the change in the value of the K_eq
B) was a decrease in the concentration of [A]
C) was a decrease in the concentration of [B]
D) was an increase in the concentration of [AB]

Question 13

Reaction conditions for a hypothetical reaction, A + B $\rightarrow$ C, are given below.

Predict which reaction should occur at the slowest rate. (M = molarity)

A) 1
B) 2
C) 3
D) 4

Question 14

Chemical equilibrium is reached in a system when ________.

A) product and reactant concentrations remain constant
B) reactant concentrations steadily decrease
C) product molecules begin reacting with each other
D) complete conversion of reactants to products has occurred

Question 15

A mixture of 1.40 moles of A and 2.30 moles of B was allowed to reach equilibrium. At equilibrium, it is found that 0.90 mole of A is present. How many moles of C are present at equilibrium?
3 A (g) + 2 B (g) $\rightarrow$ 4 C (g)

A) 1.60 moles
B) 0.667 mole
C) 1.10 moles
D) 1.30 moles

Question 16

A chemical equilbrium expression depends on the ________ of a reaction.

A) rate
B) stoichiometry
C) stoichiometry and mechanism
D) mechanism

Question 17

Given the following reaction, the equilibrium expression will be:
4 CuO (s) + CH₄ (g) $\rightarrow$ CO₂ (g) + 4 Cu (s) + 2 H₂O (g)

A) [CuO]/[Cu]
B) [CuO]⁴/[Cu]⁴
C) [Cu]⁴/[CuO]⁴
D) [CO₂][H₂O]²/[CH₄]

Question 18

Which of the following is the correct equilibrium expression for the reaction
CS₂ (g) + 4 H₂ (g) $\rightarrow$ CH₄ (g) + 2 H₂S (g)

A)
B)
C)
D)

Question 19

Which of the following is the correct equilibrium expression for the reaction
2 Ag (s) + Cl₂ (g) $\rightarrow$ 2 AgCl (s)

A)
B)
C)
D)

Question 20

Identify the reaction that is described by the following equilibrium expression:
K = [H₂]² [O₂] / [H₂O]²

A) 2 H₂ (g) + O₂ (g) $\rightarrow$ 2H₂O (g)
B) H₂O (g) $\rightarrow$ H₂ (g) + O₂ (g)
C) H₂O (g) $\rightarrow$ 2H (g) + O (g)
D) 2H₂O (g) $\rightarrow$ 2 H₂(g) + O₂ (g)

Question 21

If, at equilibrium most of the reactants remain unreacted, the equilibrium constant would be expected to have ________.

A) a very large numerical value
B) a very small numerical value
C) a numerical value slightly greater than 1.0
D) a numerical value slightly less than 1.0

Question 22

When the position of an equilibrium is described as being "far to the left" it means that ________.

A) very few reactant molecules are present in the equilibrium mixture
B) very few product molecules are present in the equilibrium mixture
C) significant amounts of both products and reactants are present in the equilibrium mixture
D) the rate of the reverse reaction is greater than that of the forward reaction

Question 23

The grams of products present after a chemical reaction reaches equilibrium ________.

A) will always be greater than the grams of reactants present
B) will always be less than the grams of reactants present
C) must equal the grams of reactants present
D) may be less than, equal to, or greater than the grams of reactants present, depending upon the chemical reaction under study

Question 24

Which statement is false? An equilibrium constant for a particular reaction ________.

A) changes when the temperature increases
B) changes when a catalyst is added
C) does not change when an additional quantity of a reactant is added
D) does not change when a product is removed

Question 25

What is the equilibrium constant value if at equilibrium the concentrations are NH₃ = 0.40 M, H₂ = 0.12 M and N₂ = 0.040 M at a certain temperature?
2 NH₃ (g) $\rightarrow$ N₂ (g) + 3 H₂ (g)

A) 4.8 x 10^-2
B) 4.3 x 10^-4
C) 6.8 x 10^-9
D) 7.2 x 10¹⁵

Question 26

Calculate the equilibrium constant for the reaction below if a 3.25 L tank was found to contain 0.343 mol O₂, 0.0212 mol SO₃ and 0.00419 mol SO₂ at equilibrium.
2 SO₃ (g) $\rightarrow$ 2 SO₂ (g) + O₂ (g)

A) 6.78 x 10^-2
B) 1.34 x 10^-2
C) 4.12 x 10^-3
D) 4.35 x 10^-2

Question 27

Given the following decomposition reaction: PCl₅ (g) $\rightarrow$ PCl₃ (g) + Cl₂ (g), when 0.84 moles of PCl₅ is placed in a 1.0 it was found that when the reaction reaches equilibrium, 0.72 moles of PCl₅ still remains. What is the value of the equilibrium constant for this reaction?

A) 0.62
B) 0.72
C) 0.020
D) 0.12

Question 28

For a reaction which has an equilibrium constant of 3.8 x 10^-16 at 25 °C, the position of equilibrium is best described as ________.

A) mostly products
B) mostly reactants
C) same amount of products and reactants
D) significant amounts of both products and reactants

Question 29

All of the following factors may shift the position of an equilibrium except one. The exception is ________.

A) reduction of reaction volume
B) increase reaction temperature
C) double the pressure (assume moles of reactants > products)
D) addition of a catalyst

Question 30

What effect does a catalyst have on an equilibrium?

A) It increases the rate at which an equilibrium is reached without changing the composition of the reaction.
B) It slows the reverse reaction.
C) It increases the rate of the forward reaction.
D) It shifts the reaction to the right.

Question 31

If at equilibrium, reactant concentrations are slightly smaller than product concentrations, the equilibrium constant would be ________.

A) a number >> 1
B) a number << 1
C) a number slightly lower than one
D) a number slightly higher than one

Question 32

The form of the expression for the equilibrium constant, K_eq, for the reaction below is:
4 NH₃ (g) + 5 O₂ (g) $\rightarrow$ 4 NO (g) + 6 H₂O (g)

A)
B)
C)
D)

Question 33

The form of the expression for the equilibrium constant, K_eq, for the reaction below is:
2 NaIO₃ (s) $\rightarrow$ 2 NaI (s) + 3 O₂ (g)

A)
B)
C)
D) K_eq = [O₂]³

Question 34

At a given temperature, K = 46.0 for the reaction:
4 HCl (g) + O₂ (g) $\rightarrow$ 2 H₂O (g) + 2 Cl₂ (g)
At equilibrium, [HCl] = 0.150, [O₂] = 0.395, and [H₂O] = 0.625. What is the concentration of [Cl₂] at equilibrium?

A) 1.26 M
B) 0.00653 M
C) 0.153 M
D) 0.438 M

Question 35

Sulfur combines with hydrogen to form hydrogen sulfide, a toxic gas that is a product of decay of organic material.
S₂ (g) + 2 H₂ (g) $\rightarrow$ 2 H₂S (g) K = 2.8 x 10^-21
Which of the following statements is true concerning the equilibrium system?

A) Increasing the volume of the sealed reaction container would shift the equilibrium to the right.
B) Decreasing the concentration of H₂ would shift the equilibrium to the right.
C) Decreasing the concentration of H₂S would shift the equilibrium to the left.
D) Very little hydrogen sulfide gas is present in the equilibrium.

Question 36

Hydrogen gas reacts with iron(III) oxide and produces iron metal which can be used to produce steel according to the reaction below. Choose the response that is incorrect concerning the equilibrium system.
Fe₂O₃ (s) + H₂ (g) + heat $\rightarrow$ 2 Fe (s) + 3 H₂O (g)

A) Lowering the reaction temperature will increase the concentration of hydrogen gas.
B) Increasing the pressure on the reaction chamber favors the formation of products.
C) Continually removing water from the reaction chamber increases the yield of iron.
D) Decreasing the volume of hydrogen gas will reduce the yield of iron.

Question 37

CO₂ and H₂ are allowed to react until an equilibrium is established as follows:
CO₂ (g) + H₂ (g) $\rightarrow$ H₂O (g) + CO (g)
What will be the effect on the equilibrium by adding H₂O to the equilibrium mixture?

A) The equilibrium will shift to the left.
B) H₂ concentration will decrease and CO₂ concentration will increase.
C) CO and CO₂ concentrations will increase.
D) H₂ concentration will decrease and H₂O concentration will increase.

Question 38

According to Le Chatelier's principle, which of the following changes will shift to the left the position of the equilibrium of the reaction
N₂ (g) + 3 H₂ (g) $\rightarrow$ 2 NH₃ (g) + Heat

A) Increase the concentration of N₂.
B) Decrease the pressure on the system.
C) Decrease the temperature.
D) Increase the concentration of H₂.

Question 39

In which of the following equilibrium systems will the equilibrium shift to the left when the pressure of the system is increased?

A) N₂ (g) + 3 H₂ (g) $\rightarrow$ 2 NH₃ (g) + Heat
B) 4 NH₃ (g) + 5 O₂ (g) $\rightarrow$ 4 NO (g) + 6 H₂O (l)
C) 2 SO₂ (g) + O₂ (g) $\rightarrow$ 2 SO₃ (g)
D) H₂ (g) + Cl₂ (g) $\rightarrow$ 2 HCl (g)

Question 40

In which of the following equilibrium reactions will a shift to the left occur from a decrease in pressure?

A) 2 HCl (g) $\rightarrow$ H₂ (g) + Cl₂ (g)
B) 2 SO₃ (g) $\rightarrow$ 2 SO₂ (g) + O₂ (g)
C) N₂ (g) + 3 H₂ (g) $\rightarrow$ 2 NH₃ (g)
D) N₂O₄ (g) $\rightarrow$ 2 NO₂ (g)

Question 41

For a chemical reaction at equilibrium, which of the following would always decrease the concentrations of the products?

A) Increase the temperature.
B) Decrease the temperature.
C) Decrease the pressure.
D) Decrease the concentration of a reactant.

Question 42

The following reaction is endothermic: CaCO₃ (s) $\rightarrow$ CaO (s) + CO₂ (g). Which of the following will cause the reaction to shift towards making more carbon dioxide gas?

A) increasing the temperature of the reaction
B) decreasing the temperature of the reaction
C) increasing the pressure of the system
D) increasing both the pressure and temperature of the system

Question 43

Consider the following chemical system at equilibrium.
Heat + 6 H₂O (g) + 2 N₂ (g) $\rightarrow$ 4 NH₃ (g) + 3O₂ (g)
Which of the following stresses would shift the equilibrium to the left?

A) increasing the concentration of O₂
B) increasing the reaction temperature
C) increasing the concentration of H₂O
D) decreasing the concentration of NH₃

Question 44

Consider the following system at equilibrium: N₂ (g) + 3 H₂ (g) $\rightarrow$ 2 NH₃ (g) + 92. 94 kJ
Which of the following changes will shift the equilibrium to the right?
1) Increasing the temperature     2. Decreasing the temperature
3) Increasing the volume     4. Decreasing the volume
5) Removing some NH₃     6. Adding some NH₃
7) Removing some N₂     8. Adding some N₂

A) 1, 4, 6, 7
B) 2, 3, 5, 8
C) 1, 6, 8
D) 2, 4, 5, 8

Question 45

Coal burning plants release sulfur dioxide, a toxic gas, into the atmosphere. Nitrogen monoxide is released into the atmosphere via industrial processes and the combustion engine. Sulfur dioxide can also be produced in the atmosphere by the reaction of sulfur trioxide and nitrogen monoxide according to the following equilibrium.
SO₃ (g) + NO (g) + heat $\rightarrow$ SO₂ (g) + NO₂ (g)
Which of the following stresses will not shift the equilibrium to the right?

A) decrease the reaction chamber volume (pressure increase)
B) temperature increase
C) [NO₂] decrease
D) [NO] increase

Question 46

Which of the following conditions would force to completion the reaction?
2 N₂ (g) + 6 H₂O (g) + heat $\rightarrow$ 4 NH₃ (g) + 3 O₂ (g)

A) continual removal of N₂ gas
B) decrease the pressure on the reaction vessel
C) continual addition of NH₃ gas to the reaction mixture
D) increase reaction temperature

Question 47

a) Draw an energy diagram for the following reaction, whose activation energy is 75 kJ/mol and whose overall energy for the reaction is exothermic. Be sure to label all parts of the graph.
b) How does a catalyst speed up a reaction? Explain and illustrate it on your graph.
H2 (g) + I2 (g) ? 2 HI (g) + heat
Draw an activation diagram and then show how a catalyst speeds up a reaction by lowering the activation energy of a reaction.

Question 48

A 0.20 mole sample of C and a 0.10 mole sample of B are placed in a reaction chamber. At equilibrium, 0.080 mole of A is present. What is the composition of the equilibrium mixture in terms of moles of each substance present.
4 C (g) + B ⇌ 2 A (g)

Question 49

The value of the equilibrium constant (K) for the reaction
N₂O₄ (g) ⇌ 2 NO₂
is ________ if the concentrations of each species at equilibrium are [N₂O₄] = 0.300 and [NO₂] = 0.0054. The value of (K) indicates that the ________ reaction is favored.

Question 50

Write the expression for the equilibrium constant for the following reaction.
CuO (s) + H₂ (g) ⇌ Cu (s) + H₂O (g)

Question 51

Write the expression for the equilibrium constant for the following reaction.
2 Na₂O (s) ⇌ 4 Na (l) + O₂ (g)

Question 52

For the equilibrium shown below the equilibrium constant is 8.5 x 10^-3. If 0.055 mol of IBr is placed in a 3.00 L container, what is the concentration of each substance after equilibrium is reached?
2 IBr (g) ? I₂ (g) + Br₂ (g)