19 - Equilibrium

Question 1

The Equilibrium Constant (Kc)

Answer 1

The equilibrium constant (Kc) is a numerical value that expresses the ratio of product concentrations to reactant concentrations at equilibrium. It is specific to a given reaction at a particular temperature.

Question 2

Units for Kc in the equation
H2(g) + I2(g) -> 2HI(g)

Answer 2

no units

Question 3

Units for Kc in the equation
N2O4(g)->2NO2(g)

Answer 3

moldm-3

Question 4

Units for Kc in the equation
2SO2(g)+ O2 -> 2SO3(g)

Answer 4

dm3mol-1

Question 5

What is homogeneous equilibria?

Answer 5

Homogeneous equilibrium occurs when all the reactants and products in a chemical reaction exist in the same physical state (e.g., all gases, all aqueous solutions, or all in the gas phase).

Question 6

What is heterogeneous equilibrium?

Answer 6

heterogeneous equilibrium occurs when the reactants and products in a chemical equilibrium exist in different physical states, such as a combination of gases, liquids, and solids.

Question 7

Provide an example of a homogeneous equilibrium reaction

Answer 7

the dissociation of nitrogen dioxide (NO2) into nitrogen dioxide molecules and nitrogen tetroxide (N2O4) in the gas phase:
2NO2(g)⇌N2O4(g)

Question 8

Give an example of a heterogeneous equilibrium reaction from

Answer 8

the formation of solid calcium carbonate (CaCO3) from calcium oxide (CaO) and carbon dioxide (CO2) gas:

CaO(s)+CO2(g)⇌CaCO3(s)

Question 9

How is the equilibrium constant (Kc) expression different for homogeneous equilibrium ?

Answer 9

In homogeneous equilibrium, the equilibrium constant expression includes only the concentrations (or partial pressures) of the gaseous reactants and products, following the balanced chemical equation.

Question 10

How do pure solids and liquids affect the equilibrium position heterogeneous equilibrium?

Answer 10

pure solids and liquids are omitted from the equilibrium constant expression, and their presence does not significantly affect the equilibrium position. The equilibrium position is determined by the concentrations of gaseous reactants and products.

Question 11

What information do you need to calculate Kc from equilibrium amounts?

Answer 11

To calculate Kc, you need the balanced chemical equation for the reaction and the concentrations (or pressures for gas-phase reactions) of the reactants and products at equilibrium.

Question 12

What is Kp?

Answer 12

Kp is the equilibrium constant for a chemical reaction when partial pressures of gases are used in the expression.

Question 13

How is Kp expressed in terms of partial pressures for a gas-phase reaction?

Answer 13

Kp is expressed as the ratio of the product partial pressures raised to the power of their coefficients in the balanced chemical equation, divided by the reactant partial pressures raised to the power of their coefficients.

Question 14

What does the magnitude of the Kp value indicate about the position of the equilibrium?

Answer 14

A larger Kp value suggests that the equilibrium favours the formation of products, while a smaller Kp value indicates that the equilibrium favours the reactants.

Question 15

What is mole fraction?

Answer 15

The ratio of the number of moles of a specific substance to the total number of moles in the system.
x= number of moles of species of gas/total number of moles in gas mixture

Question 16

What is partial pressure?

Answer 16

The pressure exerted by a single component of a gas mixture, as if it were the only gas in the container. It’s based on Dalton’s law of partial pressures, which states that in a mixture of non-reacting gases, the total pressure is the sum of the partial pressures of the individual gases.

P(A)= x(A) * P

Where x is mole fraction
and P is the total pressure

Question 17

How can you control the position of equilibrium using a catalyst?

Answer 17

A catalyst speeds up both the forward and reverse reactions but does not change the position of equilibrium. It allows the system to reach equilibrium more quickly.

Question 18

What happens to the equilibrium constant if the temperature of an exothermic reaction is increased?

Answer 18

Kc/Kp will decrease

Question 19

Explain the equilibrium shift of a reaction that is exothermic in the forward direction, where its temperature has increased.

Answer 19

• Kp decreases (Kp does opposite to temp in an exothermic reaction)
• the system is no longer in equilibria
• the ratio of the p(products)/p(reactants) > Kp
• In response the magnitude of p(products)/p(reactants) must decrease so it can equal Kc
• p(product) must decrease
• p(reactants) must increase
• the position of the equilibrium shifts towards the reactants
• a new equilibrium is reached where p(products)/p(reactants) = Kc

Question 20

Explain the equilibrium shift of a reaction that is exothermic in the forward direction, where its temperature has decrease.

Answer 20

• Kp increases (Kp does opposite to temp in an exothermic reaction)
• the system is no longer in equilibria
• the ratio of the p(products)/p(reactants) < Kp
• In response the magnitude of p(products)/p(reactants) must increase so it can equal Kc
• p(product) must increase
• p(reactants) must decrease
• the position of the equilibrium shifts towards the products
• a new equilibrium is reached where p(products)/p(reactants) = Kc

Question 21

What happens to the equilibrium constant if the temperature of an endothermic reaction is increased?

Answer 21

Equilibrium constant increases with increasing temperature

Question 22

Explain the equilibrium shift of a reaction that is endothermic in the forward direction, where its temperature has increased.

Answer 22

• Kp increases (Kp does opposite to temp in an exothermic reaction)
• the system is no longer in equilibria
• the ratio of the p(products)/p(reactants) < Kp
• In response the magnitude of p(products)/p(reactants) must increase so it can equal Kc
• p(product) must increase
• p(reactants) must decrease
• the position of the equilibrium shifts towards the towards the products
• a new equilibrium is reached where p(products)/p(reactants) = Kc

Question 23

Explain the equilibrium shift of a reaction that is endothermic in the forward direction, where its temperature has decreased.

Answer 23

• Kp decreases (Kp does opposite to temp in an exothermic reaction)
• the system is no longer in equilibria
• the ratio of the p(products)/p(reactants) > Kp
• In response the magnitude of p(products)/p(reactants) must decrease so it can equal Kc
• p(product) must decrease
• p(reactants) must increase
• the position of the equilibrium shifts towards the reactants
• a new equilibrium is reached where p(products)/p(reactants) = Kc

Question 24

how does catalyst affect equilibrium constants

Answer 24

• affect the rate of the R. but not the position of the equilibrium
• catalysts speed up both forward and backwards reaction by the same factor