Equilibria TOPIC

Question 1

What are the two conditions for equilibrium to be established in a reaction?

Answer 1

The forward and backward reactions occur at the same rate.
The concentration of reactants and products remains constant.

Question 2

In what type of system can equilibrium occur?

Answer 2

A closed system, where reactants and/or products do not come in contact with the surroundings.

Question 3

What does it mean for equilibrium to be dynamic?

Answer 3

At a microscopic level, the reaction continues as reactants are converted to products and vice versa, but at a macroscopic level, there is no observable change.

Question 4

What are some properties that remain unchanged at equilibrium on a macroscopic level?

Answer 4

Pressure, color, pH, and concentration.

Question 5

Does the reaction stop at equilibrium?

Answer 5

No, the reaction continues at the microscopic level, but the rates of forward and backward reactions are equal.

Question 6

What is physical equilibrium?

Answer 6

It is an equilibrium that involves a change in state (e.g., liquid to gas, gas to liquid) rather than a chemical reaction.

Question 7

What are the two conditions for physical equilibrium?

Answer 7

The rate of the forward process equals the rate of the backward process.
The volume of liquid remains constant.

Question 8

In what type of system can physical equilibrium occur?

Answer 8

A closed system.

Question 9

How is physical equilibrium similar to chemical equilibrium?

Answer 9

Both are dynamic at the microscopic level but appear unchanging at the macroscopic level.

Question 10

What remains constant at physical equilibrium on a macroscopic level?

Answer 10

Properties such as color.

Question 11

What is an example of physical equilibrium?

Answer 11

The equilibrium between liquid and gas, where evaporation and condensation occur at the same rate.

Question 12

What does the equilibrium constant (𝐾𝑐) tell us?

Answer 12

It tells us the ratio of the concentration of products to reactants at equilibrium.

Question 13

What is the only factor that can change the value of 𝐾𝑐

Answer 13

Temperature

Question 14

What is the general expression for the equilibrium constant for a reaction:
aA+bB⇌cC+dD?

Answer 14

𝐾𝑐 = [C]^c [D]^d/[A]^a [B]^b

Question 15

What does a large value of 𝐾𝑐 (e.g., 4.2×10^5) indicate?

Answer 15

The concentration of products is much greater than reactants, meaning the forward reaction is favored.

Question 16

What does a small value of 𝐾𝑐 (e.g. 6.9×10^−4) indicate?

Answer 16

The concentration of reactants is much greater than products, meaning the backward reaction is favored.

Question 17

What does it mean if 𝐾𝑐 =1?

Answer 17

There are equal amounts of reactants and products at equilibrium.

Question 18

How does 𝐾𝑐 change when the reaction is reversed?

Answer 18

The new equilibrium constant is the reciprocal of the original:
𝐾𝑐’=1/𝐾𝑐

Question 19

What happens to 𝐾𝑐 if the reaction equation is multiplied by a factor 𝑘?

Answer 19

𝐾𝑐 is raised to the power of 𝑘 so 𝐾𝑐’ = (𝐾𝑐)^𝑘

Question 20

How is 𝐾𝑐 affected when multiple reactions occur consecutively?

Answer 20

The equilibrium constant for the overall reaction is the product of the individual 𝐾𝑐 values:
𝐾𝑐 = 𝐾𝑐1 x 𝐾𝑐2 x 𝐾𝑐3

Question 21

What is the reaction quotient (𝑄)

Answer 21

It is the ratio of product to reactant concentrations at a given moment, even if the reaction is not at equilibrium.

Question 22

What does it mean if 𝑄<𝐾𝑐?

Answer 22

The forward reaction is favored to reach equilibrium.

Question 23

What does it mean if 𝑄>𝐾𝑐?

Answer 23

The backward reaction is favored to reach equilibrium.

Question 24

What does it mean if 𝑄=𝐾𝑐?

Answer 24

The reaction is at equilibrium.

Question 25

What does Le Châtelier’s Principle state?

Answer 25

It predicts how a reaction at equilibrium will respond to changes in temperature, pressure, or concentration.

Question 26

How does an increase in temperature affect an endothermic reaction (Δ𝐻>0)?

Answer 26

The equilibrium shifts to the product side (forward reaction is favored).

Question 27

How does a decrease in temperature affect an endothermic reaction?

Answer 27

The equilibrium shifts to the reactant side (backward reaction is favored).

Question 28

How does an increase in temperature affect an exothermic reaction (Δ𝐻<0)?

Answer 28

The equilibrium shifts to the reactant side (backward reaction is favored).

Question 29

How does a decrease in temperature affect an exothermic reaction?

Answer 29

The equilibrium shifts to the product side (forward reaction is favored).

Question 30

What is the only factor that changes the value of 𝐾𝑐?

Answer 30

Temperature

Question 31

How does an increase in pressure affect equilibrium when more gas molecules are on the product side?

Answer 31

The equilibrium shifts to the reactant side (backward reaction is favored).

Question 32

How does a decrease in pressure affect equilibrium when more gas molecules are on the product side?

Answer 32

The equilibrium shifts to the product side (forward reaction is favored).

Question 33

How does an increase in pressure affect equilibrium when more gas molecules are on the reactant side?

Answer 33

The equilibrium shifts to the product side (forward reaction is favored).

Question 34

How does a decrease in pressure affect equilibrium when more gas molecules are on the reactant side?

Answer 34

The equilibrium shifts to the reactant side (backward reaction is favored).

Question 35

What happens if the concentration of reactants increases or the concentration of products decreases?

Answer 35

The forward reaction is favored, and equilibrium shifts to the product side.

Question 36

What happens if the concentration of products increases or the concentration of reactants decreases?

Answer 36

The backward reaction is favored, and equilibrium shifts to the reactant side.

Question 37

How does adding a catalyst affect equilibrium?

Answer 37

It speeds up both the forward and backward reactions but does not change the position of equilibrium.

Question 38

What is the main effect of a catalyst in a reaction at equilibrium?

Answer 38

Equilibrium is reached faster.

Question 39

What does the equilibrium constant 𝐾𝑐 represent in a chemical reaction?

Answer 39

It represents the ratio of the concentrations of products to reactants at equilibrium.

Question 40

How can the equilibrium constant 𝐾𝑐 be calculated from equilibrium concentrations?

Answer 40

By substituting the equilibrium concentrations of reactants and products into the equilibrium expression.

Question 41

What does ICE stand for in calculating equilibrium concentrations?

Answer 41

Initial, Change, and Equilibrium.

Question 42

What does the change in concentration represent in the ICE table?

Answer 42

The amount of a compound that reacts to reach equilibrium; it is negative for reactants and positive for products.

Question 43

How do you calculate the equilibrium constant when given initial and equilibrium concentrations?

Answer 43

Write the balanced equation, create the ICE table, calculate the changes in concentration, and then substitute equilibrium concentrations into the equilibrium expression.

Question 44

What is the algebraic approach when the equilibrium concentrations are not given, but 𝐾𝑐 and initial concentrations are provided?

Answer 44

Use a variable (e.g., 𝑥) to represent the change in concentration and solve algebraically.

Question 45

In reactions where 𝐾𝑐 is very small (e.g., 10^−3), what assumption can be made about the equilibrium concentrations?

Answer 45

The initial concentration of reactants can be assumed to be equal to the equilibrium concentration of reactants.

Question 46

What does it mean when Δ𝐺∘ = 0 for a reaction?

Answer 46

The system has reached equilibrium, and the forward and backward reactions occur at the same rate.

Question 47

What happens when Δ𝐺∘ < 0 for a reaction?

Answer 47

The reaction is spontaneous, and the equilibrium favors the products.

Question 48

What happens when Δ𝐺∘>0 for a reaction?

Answer 48

The reaction is non-spontaneous, and the equilibrium favors the reactants.

Question 49

When Δ𝐺∘ is very negative, what type of equilibrium mixture is expected?

Answer 49

Mostly products.

Question 50

What is the relationship between Δ𝐺∘ and equilibrium?

Answer 50

When Δ𝐺∘=0, the system is at equilibrium. If Δ𝐺∘ < 0, the equilibrium favors products; if Δ𝐺∘>0, it favors reactants.

Question 51

How is the standard Gibbs free energy (Δ𝐺∘) related to the equilibrium constant (𝐾𝑐)?

Answer 51

ΔG ∘=−RTln(𝐾𝑐)?, where R is the universal gas constant and T is the temperature in Kelvin.

Question 52

What does 𝐾𝑐 > 1 imply about the equilibrium mixture?

Answer 52

The equilibrium favors the products, meaning there are more products than reactants.

Question 53

What does 𝐾𝑐 < 1imply about the equilibrium mixture?

Answer 53

The equilibrium favors the reactants, meaning there are more reactants than products.

Question 54

What does 𝐾𝑐 = 1 imply about the equilibrium mixture?

Answer 54

The equilibrium contains similar amounts of products and reactants.

Question 55

What is the relationship between the rate constants 𝑘 and 𝑘′ in the equilibrium constant expression?

Answer 55

𝐾𝑐=𝑘/𝑘' where 𝑘 is the rate constant for the forward reaction and 𝑘′ is the rate constant for the backward reaction.

Question 56

How does the equilibrium constant 𝐾𝑐 relate to the rates of the forward and backward reactions?

Answer 56

The equilibrium constant is determined by the ratio of the rate constants for the forward and backward reactions.

Question 57

At equilibrium, what is true about the rate of the forward reaction and the rate of the backward reaction?

Answer 57

The rate of the forward reaction is equal to the rate of the backward reaction.

Question 58

How does the equilibrium constant give information about the relative rates of forward and backward reactions?

Answer 58

The magnitude of 𝐾𝑐 reflects the ratio of the rate constants, but it doesn't directly provide information about the individual reaction rates.