Chemical Equilibria, Le Chatelier's Principle & Kc PHYSICAL

Question 1

What is a reversible reaction?

Answer 1

A reaction in which the products can react to reform the original reactants

Question 2

What symbol is used to represent a reversible reaction?

Answer 2

⇌

Question 3

What is happening in a dynamic equilbrium?

Answer 3

The rate of forward reaction is the same as rate of backward reaction in closed system
Concentrations of reactants and products is constant

Question 4

What is a closed system?

Answer 4

A system in which none of the reactants or products escape from reaction mixture

Question 5

What is an open system?

Answer 5

A system in which matter and energy can be lost to surroundings

Question 6

Can equilibrium be reached in an open system taking place entirely in solution?

Answer 6

Equilibrium can be reached as negligible amount of material is lost through evaporation

Question 7

Can equilbrium be reached in an open system involving gases?

Answer 7

No

Question 8

What is meant by constant concentrations?

Answer 8

Not changing
Not equal

Question 9

When do concentrations stop changing in a reaction?

Answer 9

When equilibrium is reached

Question 10

What is meant by position of equilibrium?

Answer 10

The relative amounts of products and reactants in an equilbrium mixture

Question 11

What effect is seen on concentration when the position of equilbrium shifts left?

Answer 11

Concentration of reactants increases

Question 12

What effect is seen on concentration when the position of equilbrium shifts right?

Answer 12

Concentration of products increases

Question 13

What does Le Chatelier’s principle state?

Answer 13

If a change is made to a system in dynamic equilbrium, the position of equilbrium moves to counteract this change

Question 14

What is Le Chatelier’s principle used to predict?

Answer 14

Changes to the position of equilbrium when there are changes in temperature, pressure or concentration

Question 15

How does the equilbrium shift when there is an increase in reactant concentration?

Answer 15

Shifts right

Question 16

How does the equilbrium shift when there is a decrease in reactant concentration?

Answer 16

Shifts left

Question 17

How does the equilbrium shift when there is an increase in pressure?

Answer 17

Shifts in direction that produces smaller number of molecules of gas to decrease pressure

Question 18

How does the equilbrium shift when there is a decrease in pressure?

Answer 18

Shifts in direction that produces larger number of molecules of gas to increase pressure

Question 19

How does the equilbrium shift when there is an increase in temperature?

Answer 19

Equilbrium moves in endothermic direction

Question 20

How does the equilbrium shift when there is a decrease in temperature?

Answer 20

Equilbrium moves in exothermic direction

Question 21

How do catalysts effect equilbrium?

Answer 21

Cause reaction to reach equilibrium faster

Question 22

How do catalysts effect the position of equilbrium?

Answer 22

No effect

Question 23

Do catalysts increase the rate of forward or reverse reaction more?

Answer 23

Increase both equally

Question 24

What is the equilbrium constant expression?

Answer 24

Links the equilbrium constant to the concentrations of reactants and products at equilbrium

Question 25

What does the equilibrium constant expression take into account?

Answer 25

Stoichiometry of equation

Question 26

What is the equilibrium constant expression for aA + bB ⇌ cC + dD?

Answer 26

K = [C]ᶜ[D]ᵈ/[A]ᵃ[B]ᵇ

Question 27

What do [A] and [B] represent in K = [C]ᶜ[D]ᵈ/[A]ᵃ[B]ᵇ?

Answer 27

Equilbrium reactant concentrations

Question 28

What do [C] and [D] represent in K = [C]ᶜ[D]ᵈ/[A]ᵃ[B]ᵇ?

Answer 28

Equilbrium product concentrations

Question 29

What do a, b, c and d represent in K = [C]ᶜ[D]ᵈ/[A]ᵃ[B]ᵇ?

Answer 29

Number of moles of corresponding reactants and products

Question 30

What are ignored in equilbrium constant expressions?

Answer 30

Solids

Question 31

What do the units of Kc depend on?

Answer 31

The form of the equilbrium expression

Question 32

What can be used if questions give the initial and equilbrium concentrations of reactants but not products?

Answer 32

An initial, change and equilibrium table

Question 33

How is equilibrium constant affected by changes in concentrations?

Answer 33

It isn't affected if all other conditions stay the same

Question 34

How is equilibrium constant affected by changes in pressure?

Answer 34

It isn't affected if all other conditions stay the same

Question 35

How is equilibrium constant affected by changes in temperature?

Answer 35

Endothermic reactions increase equilbrium constant Exothermic reactions decrease equilbrium constant

Question 36

How is equilibrium constant affected by the presence of a catalyst?

Answer 36

It isn't affected if all other conditions stay the same

Question 37

Do catalysts speed up the forward or reverse reactions more?

Answer 37

Speed up both at same rate so ratio of products to reactants remains the same

Question 37

What is the equation for the synthesis of ammonia in the Haber process?

Answer 37

N­₂ (g) + 3H₂ (g) ⇌ 2NH₃ (g)

Question 38

What is applied to get the best yield of ammonia in the Haber process?

Answer 38

Le Chatelier's principle

Question 39

How is pressure altered to maximise the ammonia yield in the Haber process?

Answer 39

Increased

Question 40

How does increasing pressure of the Haber process maximise the yield of ammonia?

Answer 40

Shifts to direction with fewest molecules of gas formed to reduce pressure - towards right so yield of ammonia increases Particles closer together, more successful colisions to increase reaction rate

Question 41

Why is there a compromise pressure of 200atm in the Haber process?

Answer 41

Very high pressures are expensive to produce

Question 42

How is temperature altered to maximise the ammonia yield in the Haber process?

Answer 42

Lowered

Question 43

How does decreasing temperature of the Haber process maximise the yield of ammonia?

Answer 43

Decrease energy of surroundings so reaction shifts where energy is released to counteract this Exothermic reaction so shifts right

Question 44

Why is there a compromise temperature of 400-450ᵒC in the Haber process?

Answer 44

Gases need enough kinetic energy to collide and react to reach equilibrium

Question 45

What does a heat exchanger do?

Answer 45

Warms incoming gas mixture to give molecules more kinetic energy so collide more increasing likelihood of reaction

Question 46

How is ammonia removed during Haber process?

Answer 46

By condensing into liquid

Question 47

How does removing ammonia from the Haber process maximise the yield of ammonia?

Answer 47

Shifts equilibrium position to right to replace ammonia More ammonia formed from hydrogen and nitrogen

Question 48

How is the recovered ammonia stored in Haber process?

Answer 48

Very low temperatures No catalyst present

Question 49

Why is recovered ammonia stored at low temperature without catalyst?

Answer 49

Slows decomposition reaction of ammonia back into hydrogen and nitrogren

Question 50

Give the three equations of the synthesis of sulfuric acid in the Contact process.

Answer 50

2SO­₂(g) + O₂(g) ⇌ 2SO₃(g) SO₃ + H₂SO₄ → H₂S₂O₇ H₂S₂O₇ + H₂O → 2H₂SO₄

Question 51

How is pressure altered to maximise the sulfuric acid yield in the Contact process?

Answer 51

Increase

Question 52

How does the increase of pressure maximise the sulfuric acid yield in the Contact process?

Answer 52

Shifts to direction with fewest molecules of gas formed to reduce pressure - towards right so yield of sulfur trioxide increases

Question 53

Why is there a compromise temperature of 400-450ᵒC in the Contact process?

Answer 53

Gases need enough kinetic energy to collide and react to reach equilibrium

Question 54

How is temperature altered to maximise the sulfuric acid yield in the Contact process?

Answer 54

Lowered

Question 55

How does decreasing temperature of the Contact process maximise the yield of sulfuric acid?

Answer 55

Decrease energy of surroundings so reaction shifts where energy is released to counteract this Exothermic reaction so shifts right

Question 56

What catalyst is used in the Contact process?

Answer 56

Vanadium oxide