Chapter 19 - Equilibrium

Question 1

How do you calculate Kc?

Answer 1

[D]^d x [E]^e

[A]^a x [B] ^b

Question 2

How do you calculate the units for Kc?

Answer 2

Substitute units into the Kc expression, cancel common units and show the final answer on one line

Question 3

What are the two types of equilibria?

Answer 3

Homogeneous and heterogeneous equilibria

Question 4

What is a homogeneous equilibrium?

Answer 4

The equilibrium species all have the same state

Question 5

What is a heterogeneous equilibrium?

Answer 5

The equilibrium species can be in different states

Question 6

What is important to remember about calculating Kc for heterogeneous equilibria?

Answer 6

You don’t consider the concentrations of liquids or solids, just gases and those in the aqueous state

Question 7

What is Kp?

Answer 7

The equilibrium constant in terms of partial pressures

Question 8

What is the mole fraction of a gas?

Answer 8

The proportion by volume to the total volume of gas in a gaseous mixture

Question 9

How do you calculate a gas’ mole fraction?

Answer 9

Number of moles of A /

Total number of moles in the gaseous mixture

Question 10

What will the mole fractions of all the chemicals in equilibrium equal?

Answer 10

1

Question 11

What is the partial pressure of a gas?

Answer 11

The contribution that a gas makes towards the total pressure

Question 12

What will the partial pressures of all the chemicals in equilibrium equal?

Answer 12

The total pressure

Question 13

How do you calculate partial pressure?

Answer 13

Mole fraction of A x total pressure

Question 14

What species can be substituted into the Kp expression?

Answer 14

Gases only

Question 15

How do you calculate Kp?

Answer 15

p(C)^c x p(D)^d /

p(A)^a x p(B)^b

Question 16

What are suitable units for Kp?

Answer 16

Kilopascals (kPa) or atmospheres (atm)

Question 17

What does a K value of 1 mean?

Answer 17

An equilibrium halfway between products and reactants

Question 18

What does a K value larger than 1 mean?

Answer 18

An equilibrium in favour of the products

Question 19

What does a K value less than 1 mean?

Answer 19

An equilibrium in favour of the reactants

Question 20

When will the value of K change?

Answer 20

When the temperature changes

Question 21

If the forward reaction is exothermic, what happens when you increase the temperature?

Answer 21

The equilibrium constant decreases
The yield of the products decreases
The position of equilibrium shifts to the left

Question 22

What happens to the equilibrium constant if you change the pressure or concentration?

Answer 22

It doesn’t change

Question 23

Explain why changing the concentration of one of the species at equilibrium shifts the position of equilibrium

Answer 23

First, work out the initial value of K
Then, work out the new value of K using the given concentrations
If this is less than the original value of K, the numerator must increase and the denominator decreases
This shifts the equilibrium to the right, and vice-versa if the new value of K is more than the original value

Question 24

How does a catalyst affect the equilibrium constant?

Answer 24

They affect the rate of the reaction but not the position of equilibrium because they increase the forward and reverse reactions by the same rate

Question 25

Explain why changing the pressure of one of the species at equilibrium changes the position of the equilibrium

Answer 25

First, work out the initial value of Kp
Then, work out the new value of Kp using the given pressures
If this is less than the original value of K, the numerator must increase and the denominator decreases
This shifts the equilibrium to the right, and vice-versa if the new value of Kp is more than the original value

Question 26

Explain why increasing the temperature of an equilibrium where the forward reaction is endothermic will shift the equilibrium

Answer 26

Increasing the temperature increases the value of Kp
The numerator must increase
The denominator must decrease
The equilibrium shifts towards the products (to the right)

Question 27

Explain why increasing the temperature of an equilibrium where the forward reaction is exothermic will shift the equilibrium

Answer 27

Increasing the temperature will decrease the value of K
The numerator must decrease
The denominator must increase
The equilibrium shifts towards the reactants (to the left)