5.1 - Reaction rates and equilibrium (quantitative)

Question 1

Do you know how to write and expression and calculate Kc ?

Answer 1

Yes

Question 2

Do you know how to find the units of Kc ?

Answer 2

Yes

Question 3

What are the two types of equilibria ?

Answer 3

• Homogenous equilibria
• Heterogeneous equilibria

Question 4

Define the term ‘Homogenous equilibria’ ?

Answer 4

Homogenous equilibria - A homogeneous equilibrium contains equilibrium species that all have the same state or phase

Question 5

Define the term ‘Heterogeneous equilibria’ ?

Answer 5

Heterogenous equilibria - A heterogeneous equilibrium contains equilibrium species that have different states or phases

Question 6

Do you know how to calculate equilibrium quantities and therefore Kc ?

Answer 6

Yes

Question 7

What is mole fraction ?

Answer 7

The mole fraction of a gas is the proportion by volume to the total volume of gases in a gas mixture

Question 8

What is the equation for mole fraction ?

Answer 8

Question 9

What is partial pressure ?

Answer 9

• The partial pressure p of a gas is the contribution that the gas makes towards the total pressure P
• The sum of the partial pressures of each gas equals the total pressure.

Question 10

What is the equation for partial pressure ?

Answer 10

Question 11

Do you know how to write an expression for Kp ?

Answer 11

Yes

Question 12

Do you know how to calculate Kp?

Answer 12

Yes

Question 13

What factors effect the equilibrium position ?

Answer 13

• Concentration ( of reactants/ products )
• Pressure
• Temperature

Question 14

What factors effect the equilibrium constant ?

Answer 14

Only temperature

Question 15

What does the magnitude of the equilibrium constant show ?

Answer 15

The magnitude of the equilibrium constant indicates the relative position of the equilibrium

Question 16

Explain what the different values of the equilibrium constant show about the equilibrium position ?

Answer 16

• K= 1 indicates an equilibrium halfway between reactants and
• K > 1 indicates an equilibrium well in favour of the products/ equilibrium position towards the products
• K < 1 indicates an equilibrium well in favour of the reactants/ equilibrium position towards the reactants

Question 17

Explain what happens to the equilibrium constant when the temperature of an exothermic reaction is increased ?

Answer 17

• The equilibrium constant decreases as the temperature increases
• The system is no longer in equilibrium
• The partial pressure/ concentration of the product, must decrease.
• The partial pressures/ concentration of the reactants, must increase.
• The position of equilibrium shifts towards the reactants (to the left)
• A new equilibrium will be reached where the value of the expression equal the new equilibrium constant value

Question 18

Explain what happens to the equilibrium constant when the temperature of an endothermic reaction is increased ?

Answer 18

• The equilibrium constant increases with increasing temperature
• The system is no longer in equilibrium
• The partial pressure/ concentration of the product, must increase
• The partial pressures/ concentration of the reactants, must decrease.
• The position of equilibrium shifts towards the products (to the right)
• A new equilibrium will be reached where the value of the expression equal the new equilibrium constant value

Question 19

Explain what happens to the equilibrium constant when the concentration/ pressure increases ?

Answer 19

• The value of an equilibrium constant K is unaffected by changes in concentration or pressure
• The concentration/ partial pressure of the product, must increase/ decrease
• The concentration/ partial pressure of the reactant must decrease/ increase
• The equilibrium constant is restored to its original value

Question 20

Explain what happens to the equilibrium constant when the concentration/ pressure doubles ?

Answer 20

• The value of an equilibrium constant K is unaffected by changes in concentration or pressure
• Doubling of pressure/ concentration will result in a doubling of the partial pressures/ concentration of both reactants and products
• The system is no longer in equilibrium depending on the expression of the equilibrium constant
• The concentration/ partial pressure of products/ reactants must increase/ decrease to restore the value of the equilibrium constant

Question 21

What is the effect of a catalyst on the equilibrium constant ?

Answer 21

• Equilibrium constants are unaffected by the presence of a catalyst.
• Catalysts affect the rate of a chemical reaction but not the position of equilibrium.
• Catalysts speed up both the forward and reverse reactions in the equilibrium by the same factor.