Equilibria

Question 1

What reaction studied in class is the Haber Process

Answer 1

Nitrogen + Hydrogen ⇌ ammonia

Question 2

If you increase the temperature how will equilibrium be affected

Answer 2

It will favour the endothermic direction (backwards reaction)

Question 3

If you decrease the temperature how will equilibrium be affected

Answer 3

It will favour the exothermic direction (forwards reaction)

Question 4

If you increase the concentration how will equilibrium be affected

Answer 4

It will favour the direction that uses up the substance that has been added.
(If more products were added then it would favour the backwards reaction)

Question 5

If you decrease the concentration how will equilibrium be affected

Answer 5

It will favour the direction that forms more of the substance that has been removed.
(If products were taken away then it would favour the forwards reaction)

Question 6

If you increase the pressure how will equilibrium be affected

Answer 6

It will favour the direction that forms the fewest moles of gas.
(If there were more moles of gas in the products it would favour the forward reaction)

Question 7

If you decrease the pressure how will equilibrium be affected

Answer 7

It will favour the direction that forms more gas molecules
(If there were more gas molecules in the products it would favour the backwards reaction)

Question 8

What are reversible reactions

Answer 8

Where the products can react to reform the reactants
Both forward and backward reactions occur at the same time

Question 9

What does this symbol mean: ΔH-

Answer 9

Exothermic reaction

Question 10

What does this symbol mean: ΔH+

Answer 10

Endothermic reaction

Question 11

What does exothermic mean

Answer 11

Energy is being released

Question 12

What does endothermic mean

Answer 12

Energy is being taken in

Question 13

When is the only time pressure can become a factor affecting equilibrium

Answer 13

If ALL elements are gaseous (g)

Question 14

Dynamic equilibrium can only occur in a …

Answer 14

Closed system
(In an open system gases could escape so equilibrium would not be achieved)

Question 15

What is dynamic equilibrium

Answer 15

The point at which there is the same amount of reactants as products

Question 16

Why are the reaction conditions on an industrial scale controlled

Answer 16

To obtain an acceptable yield of product in an acceptable time

Question 17

Why is a compromise temperature of 450 °C used to produce the best yield

Answer 17

Choosing a low temp would give the most yield however the reaction is too slow
Comprise of 450 °C is chosen so that it’s not too high that not enough yield is made but not too low that it takes to long to make

Question 18

Why is a catalyst used in reversible reactions of an industrial scale

Answer 18

Increases rate of reaction, which often allows a lower temp to be used (saves energy & increases yield)

Question 19

What catalyst is often used in reversible reactions on an industrial scale

Answer 19

Iron - cheap

Question 20

Why would the yield be less than 100%

Answer 20

Incomplete reaction
Practical losses during experiment
Competing side reactions

Question 21

What is a fuel cell

Answer 21

Uses continuous supply of a fuel.
Produces a voltage for as long as the fuel & oxygen are supplied (doesn’t go flat)
Fuel doesn’t burn but energy produced from the reaction is converted to electrical energy

Question 22

Explain how a hydrogen fuel cell works

Answer 22

Hydrogen and oxygen react to produce a voltage
Water is the only product

Question 23

What are the strengths of using a hydrogen - oxygen fuel cell

Answer 23

No moving parts
Quieter
Doesn’t need recharging
Clean (only product is water)

Question 24

What are the weaknesses of using a hydrogen - oxygen fuel cell

Answer 24

Uses platinum electrodes - expensive
Hydrogen must be stored in the car
Hydrogen will run out and need replacing
Few hydrogen stations for refuelling

Question 25

Describe how a fuel cell works (step by step)

Answer 25

At the anode : hydrogen is oxidised (forms H+ ions)
Membrane only allows H+ ions to pass through to the cathode
The electrons must flow through the external circuit to the cathode
At the cathode : hydrogen & oxygen combine to form water