C3.5 The Production of Ammonia

Question 1

What is a reversible reaction?

Answer 1

One where the products of the reaction can themselves react to produce the original reactants

Question 2

What is equilibrium?

Answer 2

When the amounts of reactants and products reach a balance - their concentrations stop changing

Question 3

What conditions are needed for a point of equilibrium to be reached?

Answer 3

A closed system

Question 4

What types of reactions can reach equilibrium?

Answer 4

Reversible ones

Question 5

When is equilibrium reached?

Answer 5

When the reactions in both directions are taking place at exactly the same rate - both reactions are still happening, but the overall effect is nil because the forward and reverse reactions cancel each other out

Question 6

What does the position of equilibrium depend on?

Answer 6

The temperature and pressure of the reaction

Question 7

How can you alter conditions in a reversible reaction to change the yield of your reaction?

Answer 7

Altering the temperature and pressure of a reversible reaction can result in you producing more products that reactants

Question 8

How does altering the temperature affect a reversible reaction?

Answer 8

Increasing the temperature favours the yield of the endothermic reaction, decreasing the temperature favours the yield of the exothermic reaction

Question 9

How does altering the pressure affect a reversible reaction?

Answer 9

Raising the pressure favours the reaction which produces less volume (the least no. of molecules), lowering the pressure favours the reaction which produces more volume (the greatest no. of molecules)

Question 10

Does a catalyst change the equilibrium position?

Answer 10

Catalysts speeds up both the forward and backwards reaction by the same amount, adding a catalyst means the reaction reaches equilibrium quicker

Question 11

Do catalysts increase the amount of product produced?

Answer 11

No, you end up with the same amount of product as you would without a catalyst

Question 12

What are the optimum conditions of a reaction?

Answer 12

The conditions which make the largest amount of the desired product for the smallest input of money, energy and time

Question 13

What factors need to be considered to find the optimum conditions?

Answer 13

The temperature, pressure and rate of reaction

Question 14

What benefits are there to finding the optimum conditions of a reaction?

Answer 14

It keeps reactions running cost-effective, but can also benefit the environment

Question 15

What are the materials used in the Haber process?

Answer 15

Nitrogen and hydrogen

Question 16

How is nitrogen obtained for the Haber process?

Answer 16

It is easily obtained from the air, which is 78% nitrogen

Question 17

How is hydrogen obtained for the Haber process?

Answer 17

From natural gas (methane) or crude oil

Question 18

What is the word/symbol equation for the Haber process?

Answer 18

nitrogen + hydrogen ⇌ ammonia

N2(g) + 3H2(g) ⇌ 2NH3*(g)

Question 19

What are the conditions in the Haber process?

Answer 19

Temperature: 450°C
Pressure: 200 atmospheres
Catalyst: Iron

Question 20

Why is the temperature in the Haber process 450°C?

Answer 20

The forward reaction is exothermic, so the reaction would produce more ammonia at lower temperatures - but low temperatures means a lower rate of reaction so 450°C is compromise between maximum yield and speed of reaction

Question 21

Why is the pressure in the Haber process 200 atmospheres?

Answer 21

Higher pressures favour the forward reaction as there are less molecules of product than reactants which results in a higher yield of ammonia - but it would be too expensive to build a plant which can withstand very high pressure

Question 22

How is ammonia extracted from the reaction vessel in the Haber process?

Answer 22

It is removed as a gas, and is condensed and liquefied

Question 23

What is done with unused nitrogen and hydrogen in the reaction vessel?

Answer 23

They are recycled, which reduces waste, saves resources and reduces costs

Question 24

Why is an iron catalyst used in the Haber process?

Answer 24

Because without the catalyst the temperature would have to be raised even further to get a quick enough reaction - this would lower the percentage yield and lead to higher energy costs

Question 25

What issues are there with the Haber process and the environment?

Answer 25

Reaching the conditions required for the Haber process involves using a lot of energy which usually comes from burning fossil fuels