Chapter 19 - Equilibrium

Question 1

What does a larger Kc value mean ?

Answer 1

The further the position of equilibrium is towards the products

Question 2

What does a smaller Kc value mean ?

Answer 2

The further the position of equilibrium is towards the reactants

Question 3

What do the units of Kc depend upon ?

Answer 3

They depend upon the number of concentration terms that are in the equilibrium constant term

Question 4

How do you work out the units of Kc ?

Answer 4

• Substitute units into the expression for Kc
• Cancel common units and show the final units on a single line

Question 5

What are the two main types of equilibria ?

Answer 5

Homogenous and heterogenous

Question 6

What does a homogenous equilibrium contain ?

Answer 6

It contains equilibrium species that all have the same state or phase

Question 7

What does a heterogenous equilibrium contain ?

Answer 7

A heterogenous equilibrium contains equilibrium species that have different states or phases

Question 8

What concentrations does a homogenous equilibria contain ?

Answer 8

It contains concentrations of all species

Question 9

What concentrations does a heterogenous equilibria contain ?

Answer 9

• Any species that are in solid and liquid state are omitted from the Kc expression
• They are automatically incorporated within the overall equilibrium constant

Question 10

What states do the species have to be for them to be in the Kc expression ?

Answer 10

g or aq

Question 11

What is a mole fraction ?

Answer 11

The proportion of the volume of a gas to the total volume of gases in the mixture

Question 12

How do you work out the mole fraction ?

Answer 12

Mole fraction χ(A) = number of moles of A / total number of moles in the gas mixture

Question 13

What does the sum of the mole fractions equal to ?

Answer 13

Should equal to 1

Question 14

What does p stand for ?

Answer 14

The partial pressure of a gas

Question 15

What does P stand for ?

Answer 15

The total pressure

Question 16

What is the partial pressure ?

Answer 16

The contribution that the gas makes towards the total pressure

Question 17

How do you work out the partial pressure ?

Answer 17

• p(A) = Mole fraction of A x total pressure P
• p(A) = x(A) x P

Question 18

What does the sum of the partial pressures equal ?

Answer 18

It equals the total pressure

Question 19

What state does Kp only include ?

Answer 19

Only includes gases because only gases have partial pressures

Question 20

With the equilibrium H(2) + I(2) -> 2HI, what is the expression for Kp?

Answer 20

Kp = p(HI)^2 / p(H(2)) x p(I(2))

Question 21

What does the magnitude of an equilibrium constant represent?

Answer 21

The extent of an equilibrium

Question 22

Where does the equilibrium position shift if the concentration of a species increases ?

Answer 22

Shifts in the direction that decreases the concentration

Question 23

Where does the equilibrium position shift if the pressure is increased ?

Answer 23

Shifts towards the side with fewer gaseous moles

Question 24

Where does the equilibrium position shift if the temperature increases ?

Answer 24

Position shifts in the endothermic direction

Question 25

What does K = 1 indicate ?

Answer 25

Equilibrium halfway between reactants and products

Question 26

What does K = 100 indicate ?

Answer 26

Equilibrium well in favour of the products

Question 27

What does K = 1x10^-2 indicate ?

Answer 27

Equilibrium well in favour of the reactants

Question 28

What is K at a set temperature ?

Answer 28

Constant and does not change despite any modifications in conc, pressure or the presence of a catalyst

Question 29

What is the only condition that will cause K to change ?

Answer 29

Temperature

Question 30

What is the effect on K when the temperature is increased and the forward reaction is exothermic?

Answer 30

- Equilibrium constant decreases - Equilibrium shifts to the left

Question 31

What is the effect on K when the temperature is increased and the forward reaction is endothermic?

Answer 31

- Equilibrium constant increases - Equilibrium shifts to the right

Question 32

What effect does increasing pressure have on a reaction with fewer moles of gaseous products than reactants?

Answer 32

- Products increase - Reactants decrease - Equilibrium shifts to the right

Question 33

What effect does increasing pressure have on a reaction with more moles of gaseous products than reactants?

Answer 33

- Products decrease - Reactants increase - Equilibrium shifts to the left

Question 34

What effect does increasing pressure have on a reaction with the same number of moles of gaseous products and reactants?

Answer 34

- No change - Equilibrium stays the same

Question 35

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

Answer 35

- Catalyst affects the rate but not the equilibrium - Equilibrium is reached faster but position does not change