Chapter 19

Question 1

What are the two main types of equilibria?

Answer 1

1) homogeneous

2) heterogeneous

Question 2

What is homogeneous equilibrium?

Answer 2

Equilibrium species that all have the same state or phase

Question 3

What is heterogeneous equilibrium?

Answer 3

Equilibrium species that have different states or phases

Question 4

In heterogeneous equilibria, what states are omitted from the Kc expression?

Answer 4

1) solids

2) liquids

Question 5

Why are solids + liquids omitted from the Kc expression?

Answer 5

They are essentially constant

Question 6

How would you experimentally determine a value for Kc in the laboratory?

Answer 6

1) In a conical flask, mix together 0.100mol of both reactants
2) Add 0.0500mol of HCl(aq) as an acid catalyst to the flask
- the total volume of the mixture in the flask is 20.0cm³
3) Add 0.0500mol of HCl(aq) to a second conical flask as a control
3) Stopper both flasks and leave for a week to reach equilibrium
4) Carry out a titration on the equilibrium mixture using a standard solution of sodium hydroxide
5) Repeat the titration with the control to determine the amount of acid catalyst that had been added

Question 7

When experimentally determining a value for Kc in the laboratory, how could you modify the method to ensure that equilibrium has been reached?

Answer 7

Set up another identical experiment at the start and sample it after 2 weeks. If the result is the same, then it is safe to assume that equilibrium had been established after 1 week

Question 8

What is Kp?

Answer 8

Equilibria involving gases

Question 9

For gases, is it easier or harder to measure pressure than concentration?

Answer 9

Easier

Question 10

What is the mole fraction of a gas?

Answer 10

Its proportion by volume to the total volume of gases in a gas mixture

Question 11

mole fraction x(A) =

Answer 11

number of moles of A / total number of moles in a gas mixture

Question 12

What is partial pressure, p?

Answer 12

The contribution that a gas makes towards the total pressure

Question 13

sum of partial pressures =

Answer 13

total pressure

Question 14

partial pressure p(A) =

Answer 14

mole fraction of A x total pressure P

x(A) x P

Question 15

What volume does 1 mole of gas occupy at RTP?

Answer 15

24.0cm³

Question 16

sum of mole fractions =

Answer 16

1

Question 17

What are suitable units for partial pressures?

Answer 17

1) kilopascals (kPa)
2) pascals (Pa)
3) atmospheres (atm)

Question 18

If concentration of a species is increased, where does the position of equilibrium shift?

Answer 18

The equilibrium position shifts in the direction that reduces the concentration

Question 19

If the pressure is increased, where does the position of equilibrium shift?

Answer 19

The equilibrium position shifts towards the side with fewer gaseous moles

Question 20

If the temperature is increased, where does the position of equilibrium shift?

Answer 20

The equilibrium position shifts in the endothermic direction

Question 21

What does the magnitude of an equilibrium constant K indicate?

Answer 21

The extent of a chemical equilibrium

Question 22

What does K = 1 indicate?

Answer 22

An equilibrium halfway between reactants and products

Question 23

What does K = 100 indicate?

Answer 23

An equilibrium well in favour of the products

Question 24

What does K = 1 x 10⁻² indicate?

Answer 24

An equilibrium well in favour of the reactants

Question 25

What does the value of K give?

Answer 25

The exact position of equilibrium

Question 26

When reactants are mixed together, the reaction proceeds until what happens?

Answer 26

Until the concentrations of the equilibrium species give the value of K when placed in the equilibrium constant expression

Question 27

At a set temperature, what is constant

Answer 27

K

Question 28

When does K change?

Answer 28

If the temperature is changed

Question 29

What happens when increasing the temperature of an exothermic reaction?

Answer 29

1) K decreases
2) yield of products decreases
3) position of equilibrium shifts to the left

Question 30

What happens when increasing the temperature of an endothermic reaction?

Answer 30

1) K increases
2) yield of products increases
3) position of equilibrium shifts to the right

Question 31

How do changes in concentration and pressure affect equilibrium constants?

Answer 31

The value of an equilibrium constant K is unaffected by changes in concentration or pressure

Question 32

How does a catalyst affect equilibrium constants?

Answer 32

1) equilibrium constants are unaffected by the presence of a catalyst
2) catalysts affect the rate of a chemical reaction but not the position of equilibrium
3) catalysts speed up both the forward and reverse reactions in the equilibrium by the same factor
4) equilibrium is reached quicker but the equilibrium position is not changed