Chemical Equilibria

Question 1

What does le chateliers help to predict?

Answer 1

The shift in equilibrium when conditions are changed

Question 2

What is le chateliers principle?

Answer 2

If the conditions of a dynamic equilibrium in a closed system are changed the equilibrium will shift to oppose that change

Question 3

What are the conditions that can effect equilibrium?

Answer 3

Concentration, temperature, pressure

Question 4

What is a closed system?

Answer 4

No reactants/products can escape

Question 5

What effect does a catalyst have on the position of equilibrium?

Answer 5

A catalyst will have no effect on the position of equilibrium buy a system will reach equilibrium more quickly

Question 6

What happens at the beginning of a dynamic equilibrium?

Answer 6

The reactants react to form the products

Question 7

What happens as an equilibrium proceeds?

Answer 7

The products react to reform the reactants

Question 8

When is a dynamic equilibrium set up?

Answer 8

When the rate of the forward reaction is equal to the rate of the reverse reaction and the relative concentrations of the reactants and products remain constant

Question 9

What must the reaction take place for a dynamic equilibrium to be achieved?

Answer 9

Reaction must take place in a closed system

Question 10

What happens if the point of equilibrium is in the middle?

Answer 10

Products and reactants will reach equilibrium with the same concentration

Question 11

What happens if the point of equilibrium is to the right?

Answer 11

The products are favoured and equilibrium will be reached with the products having a greater concentration than the reactants

Question 12

What happens if the point of equilibrium is to the left?

Answer 12

The reactants are favoured and equilibrium will be reached with the reactants having a greater concentration than the products

Question 13

What are the indicators that a reaction has reached equilibrium?

Answer 13

The concentration, colour, density and pressure are all constant

Question 14

(Concentration) When will equilibrium shift to the right?

Answer 14

if the concentration of the reactants increases or the concentration of the products decreases

Question 15

(Concentration) When will equilibrium shift to the left?

Answer 15

if the concentration of the products increases or the concentration of the reactants decreases

Question 16

What happens to the equilibrium if the concentration of a reactant is increased?

Answer 16

• Equilibrium shifts to the right- More reactants reacted together to produce more product- As a result the initial change is opposed- other reactant concentrations are decreased but the products concentrations increase

Question 17

What happens to the equilibrium if the concentration of a reactant is decreased?

Answer 17

• Equilibrium shifts to the left- More product is reacted to produce more reactant- as a result the product concentration is lowered and the initial change is opposed - The product concentrations are lowered but the reactant concentrations increase

Question 18

When will a change in pressure effect equilibrium position?

Answer 18

It will only effect dynamic equilibria that contain at least one gas

Question 19

What is the prediction of shift (pressure) dependent on?

Answer 19

Number of moles of gas on each side of the equilibrium

Question 20

What happens to equilibrium position if pressure is increased?

Answer 20

• Side with the fewest moles of gas is favoured- Equilibrium opposes the change by favouring the reaction that reduces the number of moles of gas - Pressure is lowered

Question 21

What happens to equilibrium position if pressure is decreased?

Answer 21

• Side with the greatest moles of gas is favoured- Equilibrium opposes the change by favouring the reaction that increases the number of moles of gas - Pressure is increased

Question 22

What happens to the position of equilibrium if pressure is changed but both sides of the equation have an equal number of moles?

Answer 22

Changes in pressure will have no effect on equilibrium position

Question 23

As well as equilibrium position, what can pressure changes also affect?

Answer 23

Rate

Question 24

When predicting the effect of changing the temperature on equilibrium what is the prediction dependent on?

Answer 24

The delta H value

Question 25

What does a positive delta H suggest?

Answer 25

Reaction is endothermic

Question 26

What does a negative delta H suggest?

Answer 26

Reaction is exothermic

Question 27

What effect does an increase in temperature have on the position of equilibrium?

Answer 27

- Favours the endothermic reaction- Equilibrium favours the reaction that absorbs heat energy - Temperature is lowered

Question 28

What effect does a decrease in temperature have on the position of equilibrium?

Answer 28

- Favours the exothermic reaction- Equilibrium favours the reaction that releases heat energy - Temperature is increased

Question 29

What happens to an equilibrium when temperature is changed but delta H = 0?

Answer 29

Changes to temperature will have no effect on equilibrium

Question 30

As well as equilibrium, what can changes in temperature also affect?

Answer 30

Rate of reaction

Question 31

What does the hater process produce?

Answer 31

Gaseous ammonia

Question 32

What are the reactants in the haber process?

Answer 32

Nitrogen gas and hydrogen gas

Question 33

What reactant concentrations are used during the haber process and how do they compare with the ideal conditions?

Answer 33

Ideally reactant concentrations should be high to push the equilibrium to favour the products and increase the yield of ammonia. This is achieved in industry by recycling the unused nitrogen and hydrogen to maintain the high concentrations

Question 34

What product concentrations are used during the haber process and how do they compare with the ideal conditions?

Answer 34

Ideally low product concentrations will be used to push the equilibrium to favour the products and increase their yield. This is achieved in industry by cooling the products and condensing them off to maintain a low concentration

Question 35

What temperature conditions are used during the haber process and how do they compare with the ideal conditions?

Answer 35

A low temp would be ideal because the forward reaction is exothermic and a low temperature will favour the exothermic reaction and increase the ammonia yield. However, this cannot be achieved in industry because low temperature decrease the rate of the reaction. A compromise temperature Is used to balance rate and yield

Question 36

What pressure conditions are used during the haber process and how do they compare with the ideal conditions?

Answer 36

A very high pressure would be ideal because that will favour the side with the fewest moles of gas (products) and increase the yield of ammonia and the rate at which it is produced. However, high pressures can be very expensive and dangerous so a compromise pressure is used to balance yield and rate with safety and cost

Question 37

What catalyst is used in the Haber process and why?

Answer 37

A solid Iron catalyst is used (heterogeneous) it offsets the effect of the compromise temperatures and pressures and increases the rate

Question 38

What does Kc do?

Answer 38

Describes the state of the homogeneous equilibrium with respect to the concentrations of the reactants and products

Question 39

What is the Kc expression?

Answer 39

Concentration of the products each to the power of their number of moles divided by the concentration of the reactants each to the power of their number of moles

Question 40

What are the units of concentration?

Answer 40

mol.dm^-3

Question 41

What does it mean is Kc = 1?

Answer 41

Equilibrium lies exactly in the middle

Question 42

What does it mean if Kc < 1?

Answer 42

Equilibrium lies to the left

Question 43

What does it mean if Kc > 1?

Answer 43

Equilibrium lies to the right

Question 44

Which factor will affect Kc?

Answer 44

Temperature

Question 45

What happens to a reaction if temperature is increased?

Answer 45

Endothermic reaction is favoured

Question 46

What happens to a reaction if temperature is decreased?

Answer 46

Exothermic reaction is favoured