Equilibrium in Chemical Reactions: Master Dynamic Balance

Question 1

According to Le Chatelier's principle, if a change in conditions is applied to a system at equilibrium, the system will shift in a direction that:

Accepted Answer

Counters the applied change.

Answer

Favors the formation of more products.

Answer

Favors the formation of more reactants.

Answer

Has no effect on the equilibrium position.

Question 2

Which of the following factors does NOT influence the equilibrium constant of a reaction?

Accepted Answer

Presence of a catalyst

Answer

Temperature

Answer

Pressure

Answer

Concentrations of reactants and products

Question 3

Which of the following definitions best describes a catalyst?

Accepted Answer

A substance that increases the rate of a reaction without being consumed.

Answer

A substance that decreases the rate of a reaction without being consumed.

Answer

A substance that is consumed in the reaction.

Answer

A substance that does not affect the rate of a reaction.

Question 4

A reaction has an equilibrium constant of 1. What does this indicate about the reaction?

Accepted Answer

Reactants and products are present in equal concentrations at equilibrium

Answer

Reactants are favored at equilibrium

Answer

Products are favored at equilibrium

Answer

Reaction will proceed in the forward direction only

Question 5

What is the role of a catalyst in an equilibrium reaction?

Accepted Answer

Decreases the activation energy of the reaction

Answer

Increases the activation energy of the reaction

Answer

Shifts the equilibrium position

Answer

Has no effect on the equilibrium position

Question 6

Which of the following is an endothermic reaction, absorbing heat from the surroundings?

Accepted Answer

Dissolution of ammonium chloride in water

Answer

Neutralization of a strong acid and a strong base

Answer

Combustion of methane

Answer

Condensation of water vapor

Question 7

What is the effect of decreasing the temperature on an exothermic reaction, which releases heat?

Accepted Answer

Equilibrium shifts to the left, favoring the reactants

Answer

Equilibrium shifts to the right, favoring the products

Answer

Equilibrium does not shift

Answer

Reaction rate increases

Question 8

In a reversible reaction, at equilibrium, the concentrations of reactants and products are:

Accepted Answer

(c) Constant

Answer

(a) Increasing

Answer

(b) Decreasing

Answer

(d) Zero

Question 9

What role does a catalyst play in a reversible reaction at equilibrium?

Accepted Answer

(d) Has no effect

Answer

(a) Shifts the equilibrium position

Answer

(b) Increases the rate of the forward reaction

Answer

(c) Increases the rate of the reverse reaction

Question 10

Consider the reaction: 2NO(g) + O2(g) <=> 2NO2(g). What happens to the equilibrium position if the volume of the container is decreased?

Accepted Answer

(b) Shift right

Answer

(a) Shift left

Answer

(c) No change

Answer

(d) Cannot be determined

Question 11

What is a limitation of Le Chatelier's principle?

Accepted Answer

(a) It does not predict the rate of the reaction.

Answer

(b) It does not apply to heterogeneous reactions.

Answer

(c) It does not apply to reactions involving ions.

Answer

(d) It does not apply to reactions involving gases.

Question 12

Which reaction is most likely to have the largest equilibrium constant?

Accepted Answer

A reaction that preferentially forms products

Answer

A reaction that preferentially forms reactants

Answer

An exothermic reaction

Answer

An endothermic reaction

Question 13

Which of the following is a characteristic of homogeneous equilibria?

Accepted Answer

Reactants and products are in the same phase.

Answer

Reactants and products are in different phases.

Answer

The equilibrium constant is always greater than 1.

Answer

The equilibrium constant is independent of temperature.

Question 14

What is the main function of a catalyst in an equilibrium reaction?

Accepted Answer

Accelerate both the forward and reverse reactions equally.

Answer

Increase the equilibrium constant.

Answer

Shift the equilibrium position to the right.

Answer

Make the reaction irreversible.

Question 15

Which of the following is NOT an example of an equilibrium reaction?

Accepted Answer

The evaporation of water

Answer

The reaction of hydrogen and oxygen to form water

Answer

The dissolution of sugar in water

Answer

The reaction of sodium hydroxide and hydrochloric acid

Question 16

According to Le Chatelier's principle, what shift in equilibrium occurs when the concentration of a reactant is increased?

Accepted Answer

Equilibrium shifts to the right.

Answer

Equilibrium shifts to the left.

Answer

Equilibrium remains unchanged.

Answer

Equilibrium shifts in a random direction.

Question 17

Which of the following best exemplifies a heterogeneous equilibrium?

Accepted Answer

CaCO3(s) <=> CaO(s) + CO2(g)

Answer

CO(g) + O2(g) <=> CO2(g)

Answer

H2(g) + I2(g) <=> 2HI(g)

Answer

CH3COOH(aq) + H2O <=> H3O+(aq) + CH3COO-(aq)

Question 18

Which factor would most likely increase the rate of attainment of equilibrium in a reaction?

Accepted Answer

Introducing a catalyst.

Answer

Lowering the temperature.

Answer

Increasing the concentration of reactants.

Answer

Decreasing the surface area of reactants.

Question 19

What is the primary function of a catalyst in a chemical reaction?

Accepted Answer

To provide an alternative pathway for the reaction

Answer

To increase the activation energy of the reaction

Answer

To consume the reactants

Answer

To change the equilibrium position of the reaction

Question 20

Which of the following is a key characteristic of chemical equilibrium?

Accepted Answer

The forward and reverse reactions occur at equal rates

Answer

The concentrations of reactants and products change over time

Answer

The equilibrium constant is always greater than 1

Answer

The system is not in a dynamic state

Question 21

Which of the following accurately describes a system in dynamic equilibrium?

Accepted Answer

The forward and reverse reactions proceed at equivalent rates.

Answer

The concentrations of reactants and products remain unchanged over time.

Answer

No mass can enter or leave the closed system.

Answer

The system releases heat to its surroundings.

Question 22

An equilibrium constant, Kc, of 10 for a reaction indicates that:

Accepted Answer

The forward and reverse reactions occur at equal rates.

Answer

The forward reaction proceeds more rapidly.

Answer

The reverse reaction proceeds more rapidly.

Answer

The reaction is exothermic.

Question 23

Which of the following reactions represents a homogeneous equilibrium?

Accepted Answer

2NO(g) + O2(g) ⇌ 2NO2(g)

Answer

CaCO3(s) ⇌ CaO(s) + CO2(g)

Answer

Fe(s) + 2HCl(aq) → FeCl2(aq) + H2(g)

Answer

CH3COOH(aq) + NaOH(aq) → CH3COONa(aq) + H2O(l)

Question 24

What is the primary function of a catalyst in a chemical reaction?

Accepted Answer

To decrease the activation energy of the reaction

Answer

To increase the activation energy of the reaction

Answer

To alter the equilibrium position of the reaction

Answer

To accelerate only the forward reaction

Question 25

What is the key distinction between a closed and an open system in equilibrium?

Accepted Answer

An open system exchanges matter with its surroundings, unlike a closed system.

Answer

A closed system exchanges matter with its surroundings, unlike an open system.

Answer

A closed system is always in equilibrium, whereas an open system is not.

Answer

An open system is always in equilibrium, whereas a closed system is not.

Question 26

Which statement accurately describes equilibrium?

Accepted Answer

Equilibrium is a dynamic state where forward and reverse reactions balance each other.

Answer

Equilibrium is a static state where no changes occur.

Answer

Equilibrium is only possible in closed systems.

Answer

Equilibrium is spontaneously achieved in all reactions.

Question 27

Which of the following factors does NOT affect the equilibrium position of a reaction?

Accepted Answer

The presence of a catalyst

Answer

Concentration of reactants and products

Answer

Volume

Answer

Temperature

Question 28

Consider the equilibrium system: CO (g) + H2O (g) <=> CO2 (g) + H2 (g). Adding more CO to the system will:

Accepted Answer

Shift the equilibrium to the right, favoring the formation of products

Answer

Have no effect on the equilibrium position

Answer

Shift the equilibrium to the left, favoring the formation of reactants

Answer

Decrease the rate of the forward reaction

Question 29

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

Accepted Answer

CO (g) + H2O (g) <=> CO2 (g) + H2 (g)

Answer

CH4 (g) + 2O2 (g) -> CO2 (g) + 2H2O (g)

Answer

C (s) + O2 (g) <=> CO2 (g)

Answer

Zn (s) + CuSO4 (aq) <=> ZnSO4 (aq) + Cu (s)

Question 30

Which of the following statements about equilibrium is true?

Accepted Answer

At equilibrium, the forward and reverse reactions occur at the same rate.

Answer

At equilibrium, the concentrations of the reactants and products are equal.

Answer

At equilibrium, the system is always in a state of change.

Question 31

Which of the following is a limitation of Le Chatelier's principle?

Accepted Answer

It does not predict the rate of shift

Answer

It is only valid for closed systems

Answer

It only applies to homogeneous reactions

Answer

It does not apply to all chemical reactions

Question 32

A reversible reaction reaches a state of dynamic equilibrium. Which of the following statements about the reaction rates at equilibrium is true?

Accepted Answer

The forward and reverse reaction rates are equal.

Answer

The forward reaction rate is significantly faster than the reverse reaction rate.

Answer

The reaction rates are both zero.

Answer

The reverse reaction rate is significantly faster than the forward reaction rate.

Question 33

Consider the following reversible reaction: N₂(g) + 3H₂(g) ⇌ 2NH₃(g) + heat. Based on Le Chatelier's principle, how will the equilibrium position shift if the temperature is increased?

Accepted Answer

The equilibrium will shift to the left, favoring the reactants.

Answer

The equilibrium will shift to the right, favoring the products.

Answer

The equilibrium will not shift.

Question 34

Which of the following changes will NOT affect the equilibrium position of the reaction:  CO(g) + H₂O(g) ⇌ CO₂(g) + H₂(g)?

Accepted Answer

Adding a catalyst.

Answer

Increasing the pressure.

Answer

Adding more CO.

Question 35

The Haber process is used to produce ammonia (NH₃).  The reaction is exothermic and represented by: N₂(g) + 3H₂(g) ⇌ 2NH₃(g) + heat. Which set of conditions would favor the production of ammonia?

Accepted Answer

High pressure and low temperature.

Answer

High pressure and high temperature.

Answer

Low pressure and low temperature.

Answer

Low pressure and high temperature.

Question 36

A reaction system reaches equilibrium when the rate of the forward reaction is equal to the rate of the reverse reaction.  What happens to the concentrations of reactants and products at equilibrium?

Accepted Answer

The concentrations of reactants and products remain constant.

Answer

The concentration of the products increases.

Answer

The concentration of the reactants increases.

Question 37

A sealed container contains a mixture of gases at equilibrium.  The volume of the container is suddenly decreased. Which of the following changes will occur?

Accepted Answer

The equilibrium will shift to the side with fewer moles of gas.

Answer

The equilibrium will shift to the side with more moles of gas.

Answer

The equilibrium will not shift.

Question 38

The equilibrium constant (K) for a reaction is 10. What does this value imply about the reaction?

Accepted Answer

The products are favored at equilibrium.

Answer

The reactants are favored at equilibrium.

Answer

The reaction is very slow.

Answer

The reaction is very fast.

Question 39

Consider the reaction:  2NO₂(g) ⇌ N₂O₄(g) + heat. Based on Le Chatelier's principle, what will happen to the equilibrium position if more NO₂(g) is added?

Accepted Answer

The equilibrium will shift to the right, favoring the formation of N₂O₄.

Answer

The equilibrium will shift to the left, favoring the formation of NO₂.

Answer

The equilibrium will remain unchanged.

Question 40

The reaction:  H₂(g) + I₂(g) ⇌ 2HI(g) is at equilibrium.  Which of the following changes would NOT affect the value of the equilibrium constant (K)?

Accepted Answer

Adding a catalyst.

Answer

Increasing the temperature.

Answer

Increasing the pressure.

Answer

Adding more H₂.

Question 41

A chemical reaction is at equilibrium when:

Accepted Answer

The rate of the forward reaction equals the rate of the reverse reaction

Answer

The temperature of the system is constant

Answer

The concentration of reactants equals the concentration of products

Answer

No further reaction occurs

Question 42

Which of the following is NOT a factor that can affect the equilibrium position of a reaction?

Accepted Answer

Addition of a catalyst

Answer

Change in concentration

Answer

Change in volume

Answer

Change in temperature

Question 43

Consider the following reaction: CO(g) + H2O(g) ⇌ CO2(g) + H2(g). How would adding more H2O(g) to the system affect the equilibrium?

Accepted Answer

Shift to the right

Answer

No change

Answer

Catalyze the reaction

Answer

Shift to the left

Question 44

Which of the following reactions is an example of a heterogeneous equilibrium?

Accepted Answer

CaCO3(s) + 2HCl(aq) ⇌ CaCl2(aq) + CO2(g) + H2O(l)

Answer

NaOH(aq) + HCl(aq) ⇌ NaCl(aq) + H2O(l)

Answer

CH3COOH(aq) + H2O(l) ⇌ CH3COO-(aq) + H3O+(aq)

Answer

2NO(g) + O2(g) ⇌ 2NO2(g)

Question 45

What is the equilibrium constant expression for the following reaction: 2A(g) + B(g) ⇌ C(g)?

Accepted Answer

Kc = [C]/([A]^2[B])

Answer

Kc = [C]/[A][B]

Answer

Kc = [A]^2[B]/[C]

Answer

Kc = [A][B]/[C]

Question 46

Which of the following reactions is a reversible reaction?

Accepted Answer

2NO(g) + O2(g) ⇌ 2NO2(g)

Answer

NaOH(aq) + HCl(aq) → NaCl(aq) + H2O(l)

Answer

2H2(g) + O2(g) → 2H2O(g)

Answer

CaCO3(s) + 2HCl(aq) → CaCl2(aq) + CO2(g) + H2O(l)

Question 47

What is the effect of increasing the pressure on the following equilibrium: 2CO(g) + O2(g) ⇌ 2CO2(g)?

Accepted Answer

Shift to the right

Answer

Shift to the left

Answer

No change

Answer

Catalyzes the reaction

Question 48

Which of the following is a consequence of Le Chatelier's principle?

Accepted Answer

Adding heat to an endothermic reaction will shift the equilibrium to the right

Answer

Equilibrium is a static state

Answer

Changing the temperature will always affect the equilibrium position

Answer

Adding a catalyst will change the equilibrium constant