Equilibria

Question 1

Equilibrium

Answer 1

A dynamic system, where
- The concentrations of reactants and product do not change over time,
- As the rates of the forward and reverse reactions are equal

Question 2

K and Q

Answer 2

K is the equilibrium constant and is a constant at a given temperature
Q is the reaction quotient and can change over time.
If Q=K, the system is at equilbrium

Question 3

Solids and pure liquids

Answer 3

Solids and pure liquids have ean activity of 1, so is not included in the expression for K

Question 4

Changes in the position of the equilibrium

Answer 4

Temperature: increasing temperature favors the endothermic direction. Changing T, changes the value of K.
Pressure: Increasing pressure favors the side with the fewest gaseous particles

Question 5

Adding or removing reactants/products

Answer 5

Adding products, removing reactants
Q>Kc, reaction proceeds in favor of reactants. OR the system shifts the equilibrium towards the reactants to counteract the effect of the disturbance

Question 6

Catalysts

Answer 6

Increases the rate of reaction by providing an alternative pathway with a lower activation energy.
Increases the rate of both the forward and the reverse reaction so does not change the position of the equilibrium.

Question 7

What is Le Chatelier’s principle?

Answer 7

When a system at equilibrium is disturbed, it shifts in the direction that counteracts the disturbance to restore equilibrium.

Question 8

What effect does temperature have on the equilibrium mixture?

Answer 8

Shifts the equilibrium depending on the reaction’s enthalpy change.

If endothermic, it shifts right;

if exothermic, it shifts left.

Question 9

How does increasing/decreasing pressure affect a gaseous equilibrium?

Answer 9

Increasing pressure shifts the equilibrium toward the side with fewer gas molecules to minimize the disturbance.

Decreasing pressure shifts the equilibrium toward the side with more gas molecules to minimize the disturbance.

Question 10

TF

Increasing the concentration of reactants will shift the equilibrium position toward the products.

Answer 10

True

Question 11

TF

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

Answer 11

False

Question 12

TF

Le Chatelier’s Principle states that a system at equilibrium will adjust to counteract any applied change.

Answer 12

True

Question 13

TF

The equilibrium constant ( K ) changes with temperature.

Answer 13

True

Question 14

TF

In a system at equilibrium, adding more reactant will have no effect on the equilibrium position.

Answer 14

False

Question 15

TF

Decreasing the temperature of an exothermic reaction shifts the equilibrium to the left.

Answer 15

False

Question 16

TF

A catalyst has no effect on the equilibrium constant ( K ).

Answer 16

True

Question 17

TF

Pressure changes only affect equilibrium in reactions involving gases.

Answer 17

True

Question 18

What happens to the equilibrium position when a reactant is removed?

Answer 18

The equilibrium shifts to the left to produce more reactants.

Question 19

How does increasing the pressure affect the equilibrium of a reaction with more gaseous reactants than products?

Answer 19

It shifts the equilibrium toward the products.

Question 20

What is the effect of decreasing the temperature on an endothermic reaction at equilibrium?

Answer 20

The equilibrium shifts to the left, favoring the reactants.

Question 21

Write the equilibrium constant expression for the reaction

N2(g) + 3H2(g) —>—< 2NH3(g)

Answer 21

[NH3]^2
K= ————
[N2][H2]^2

Question 22

Explain Le Chatelier’s Principle in your own words.

Answer 22

SMTH

When a system at equilibrium is disturbed, it adjusts to minimize the disturbance and restore a new equilibrium.

Question 23

Why does changing the concentration of a product affect the position of equilibrium?

Answer 23

Because the system will shift to counteract the change and restore equilibrium according to Le Chatelier’s Principle.

Question 24

What does a large ( K ) value indicate about the position of equilibrium?

Answer 24

It indicates that the equilibrium lies far to the right, favoring the formation of products.

Question 25

What does it mean if a reaction has reached dynamic equilibrium?

Answer 25

The forward and reverse reactions occur at the same rate, and the concentrations of reactants and products remain constant.

Question 26

What is a reversible reaction?

Answer 26

A reversible reaction is one where reactants can form products, which in turn can react to form the original reactants.

Question 27

What does the equilibrium constant (K) represent?

Answer 27

The equilibrium constant (K) is a ratio of the concentrations of products to reactants at equilibrium, at a specific temperature.

Question 28

How does the Le Chatelier’s principle work?

Answer 28

The Le Chatelier’s principle states that if a system at equilibrium is disturbed, it will shift to counteract the disturbance and restore equilibrium.

Question 29

What does it mean for a chemical reaction to be reversible?

Answer 29

A reversible reaction can proceed in both the forward and reverse directions, forming reactants and products that can interchange.

Question 30

What is chemical equilibrium?

Answer 30

Chemical equilibrium is a dynamic state where the rate of the forward reaction equals the rate of the reverse reaction, resulting in no net change in the concentration of reactants and products.

Question 31

What does it mean when equilibrium is reached?

Answer 31

When equilibrium is reached, the concentrations of reactants and products remain constant over time because their rates of change are equal.

Question 32

How does the concentration of reactants and products behave at equilibrium?

Answer 32

At equilibrium, the concentrations of both reactants and products do not change, but they are not necessarily equal.

Question 33

Define the equilibrium constant (Kc).

Answer 33

The equilibrium constant (Kc) is a number that expresses the ratio of product concentrations to reactant concentrations, each raised to the power of their respective coefficients in the balanced equation.

Question 34

What does a large value of Kc indicate?

Answer 34

A large value of Kc suggests that, at equilibrium, the reaction favors the formation of products, with a higher concentration of products than reactants.

Question 35

What happens when Q < Kc?

Answer 35

When Q < Kc, the reaction will shift toward the products to reach equilibrium.

Question 36

What does it mean when Q > Kc?

Answer 36

When Q > Kc, the reaction will shift toward the reactants to reach equilibrium.

Question 37

What is Le Chatelier’s Principle?

Answer 37

Le Chatelier’s Principle states that when a system at equilibrium is disturbed, the system will shift its position to counteract the disturbance and restore equilibrium.

Question 38

What effect does increasing the concentration of reactants have on a reaction at equilibrium?

Answer 38

Increasing the concentration of reactants will shift the equilibrium position to favor the products, as the system tries to balance the disturbance.

Question 39

Does temperature change affect the equilibrium constant?

Answer 39

Yes, temperature change can alter the value of the equilibrium constant (K), as it is temperature dependent.

Question 40

What happens to a reaction at equilibrium when a catalyst is added?

Answer 40

Adding a catalyst does not affect the equilibrium position or the equilibrium constant, but it speeds up the rate at which equilibrium is reached.

Question 41

TF A decrease in temperature will always shift the equilibrium of an exothermic reaction to favor the products.

Answer 41

In an exothermic reaction, heat is released, and a decrease in temperature causes the system to shift toward the products to generate more heat, according to Le Chatelier’s Principle.

Question 42

Explain how Le Chatelier’s Principle can predict the effect of pressure changes on the equilibrium of a reaction involving gases.

Answer 42

Le Chatelier's Principle predicts that if pressure is increased in a system involving gases, the equilibrium will shift toward the side with fewer moles of gas to counteract the pressure change. Conversely, if pressure is decreased, the equilibrium shifts toward the side with more moles of gas.

Question 43

TF A reaction at equilibrium always has equal concentrations of reactants and products.

Answer 43

False. At equilibrium, the concentrations of reactants and products remain constant, but they are not necessarily equal. The equilibrium depends on the specific reaction and the conditions.

Question 44

TF A catalyst changes the equilibrium position of a reaction.

Answer 44

False. A catalyst speeds up the rate at which equilibrium is reached but does not affect the position of the equilibrium.

Question 45

TF If Q > Kc, the system will shift toward the reactants to reach equilibrium.

Answer 45

True. If the reaction quotient (Q) is greater than the equilibrium constant (Kc), it means there are more products than at equilibrium, so the system will shift toward the reactants.

Question 46

How does the presence of a common ion affect the solubility of a salt in solution?

Answer 46

The presence of a common ion reduces the solubility of a salt due to the common ion effect. This occurs because the added ion shifts the equilibrium of the dissolution reaction to the left, decreasing the amount of salt that dissolves.