Chapter 19 - Equilibrium

Question 1

What is homogeneous equilibria?

Answer 1

When there are equilibrium species that are all in the same state

Question 2

What is heterogeneous equilibria?

Answer 2

An equilibrium which contains species in different states or phases

Question 3

How does the KC formula change for heterogeneous equilibrium?

Answer 3

The kc equation involves concentration but the concentration of solids and liquids stay constant so they are omitted from the formula.

Question 4

How do you work out mole fraction?

Answer 4

Mole fraction = number of moles of A / total number of moles mixture

Question 5

How is measuring equilibrium of gases different to mixtures in other states?

Answer 5

Equilibria is usually expressed as Kp. In terms of partial pressure as this is easier to measure than concentration. Kp is directly proportional to Kc.

Question 6

How do you work out the partial pressure of a gas in a mixture?

Answer 6

Mole fraction A x total pressure p

Question 7

What should the sum of the mole fractions and partial pressures equal?

Answer 7

Mole fractions = 1

Partial pressures = total pressure

Question 8

What happens to solids and liquids in the Kc expression of heterogeneous equilibria?

Answer 8

Solids and liquids concentrations stays constant so they are omitted from the expression

Question 9

Under what conditions can Kc change?

Answer 9

Kc only changes if temperature changes

Question 10

If the forward reaction is exothermic what happens when the temperature increases?

Answer 10

1) The equilibrium constant decreases
2) Increasing temperature decreases the equilibrium yield of products
3) Equilibrium shifts to the left

Question 11

If the forward reaction is endothermic what happens to KP when the temperature increases?

Answer 11

1) Equilibrium constant increases
2) Raising the temperature increases the equilibrium yield of products
3) Equilibrium shifts to the right

Question 12

When increasing the temperature for an exothermic reaction what must happen to regain equilibrium at the different Kp?

(Explanations for Kc use concentration rather than partial pressure)

Answer 12

1) The ratio is now greater than Kp (because Kp has decreased)
2) The partial pressure of the products must decrease
3) The partial pressure of the reactants must increase
4) Equilibrium shifts towards the reactants
5) Equilibrium will be regained

Question 13

When increasing the temperature for an endothermic reaction what must happen to regain equilibrium?

(Explanations for Kc use concentration rather than partial pressure)

Answer 13

1) The ratio is now less than Kp
2) Partial pressure of the products must increase
3) Partial pressure of the reactants must decrease
4) The position of equilibrium shifts towards the products
5) Equilibrium is re-established

Question 14

What happens when the concentration of gaseous products are decreased?

What must happen to return to original Kc?

• use partial pressure rather than conc for Kp

Answer 14

1) Ratio is now less than KC - decreases (state what is equal to)
2) System is now no longer in equilibrium

3) Concentration of products must increase
4) Concentration of the reactants must decrease
5) Kc is restored

Question 15

What happens when the concentration of gaseous products are increased?

What must happen to return to original Kc?

• use partial pressure instead of conc for Kp

Answer 15

1) Ratio is now more than KC - increases (state what is equal to)
2) System is now no longer in equilibrium

3) Concentration of products must decrease
4) Concentration of the reactants must increase
5) Kc is restored

Question 16

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

Answer 16

1) Affect the rate of a chemical reaction but not the position of equilibrium
2) Speed up both the forward and reverse reaction in the equilibrium