Industrial Ammonia Production: Haber Process Overview

1. Syllabus/Unit: code: C2 Chemical ResourcesLesson number: 5Lesson Title: Manufacturing Chemicals - Ammonia Connector: List factors that would affect the making of a new substance

2. Keywords: • Reversible reaction • Fertiliser • Yield • Catalyst Put your hand up if there is any key word from the list that you don’t know the meaning of.

3. New Information for Learning Outcome 1 ?

4. New Information for Learning Outcomes • Haber Process Task • Research and collect information about the Haber process, include: • What is the Haber process – what is it used to make? Include a word equation and a balanced symbol equation. • Who invented the Haber process? • The product made in the Haber process – what things is it used for? • What conditions are needed for the Haber process to take place: • What does the temperature need to be? • What catalyst is needed for the reaction to happen? • What pressure is needed for the reactions? • The Haber process is a reversible reaction, what do we mean by this? • Why is a higher or lower temperature or a higher or lower pressure than those identified in part 4. used in the reaction?

5. New Information for Learning Outcomes + nitrogen hydrogen ammonia + N2(g) 3H2(g) 2NH3(g) It is made industrially by reacting nitrogen with hydrogen in the Haber process. It is a reversible reaction, so it never goes to completion. • The hydrogen comes from cracking oil fractions or from natural gas. The nitrogen comes from air. • As nitrogen is relatively unreactive, certain conditions are needed to make sure it reacts with nitrogen: • High pressure • Temperature around 450°C • Adding an iron catalyst to speed up the reaction. Recycling unreacted H2 and N2 helps reduce costs too! 03:57

6. New Information for Learning Outcomes Ammonia is one of the most important substances than humans make. Over 140 million tonnes a year are made. What are some of the uses? 03:57

7. Ammonia is often used in cleaning products because it reacts with grease making this easier to remove

8. Ammonia has other uses including hair dyes

9. Ammonia and nitric acid react together to produce ammonium nitrate which makes artificial fertiliser

10. Fertilisers are substances applied to the soil to replace the minerals plants use

11. Fertilisers are so important to food production they use 80% of all ammonia manufactured

12. + + A B C D (reactants) (products) New Information for Learning Outcome 2 Reversible reactions occur when the backwards reaction (products  reactants) takes place relatively easily under certain conditions. The products turn back into the reactants. For example, during a reversible reaction reactants A and B react to make products C and D. However, products C and D can also undergo the reverse reaction, and react together to form reactants A and B.

13. + nitrogen hydrogen ammonia + N2(g) 3H2(g) 2NH3(g) New Information for Learning Outcome 2 Conditions for the Haber process have to be carefully chosen to make sure that forward reaction is favoured. This will make sure we get the biggest yield possible (the amount of substance made in a reaction).

15. ammonia yield (%) pressure (atm) The yield of ammonia produced by the Haber process depends on the temperature and pressure of the reaction.

16. Keywords: Create Evaluate Analyse Apply Understand Remember Demonstrate your Learning for Outcome 2 Analyse (B) Why are a high pressure and 450°C temperature chosen for the Haber process? • Apply (C) • From the graph, what is the yield of ammonia at: • 100 atm. and 400°C • 400 atm. and 550°C Remember (E) What does the term ‘yield’ mean?

17. New Information for Learning Outcome 3 The highest yield of ammonia is theoretically produced by using a low temperature and a high pressure. In practice, though, these conditions are not used. Why? Lowering the temperature slows down the rate of reaction. This means it takes longer for ammonia to be produced. Increasing the pressure means stronger, more expensive equipment is needed. This increases the cost of producing the ammonia. A compromise is reached to make an acceptable yield in a reasonable timeframe while keeping costs down.

18. New Information for Learning Outcome 3 To produce a high yield of ammonia, but with a fast rate of reaction and without the need for overly expensive equipment, the Haber process is carried out at 450 °C and 200 atmospheres. The most important factor in deciding what conditions to use is therefore not yield, but total cost. What costs are involved in the industrial production of ammonia? • raw materials • equipment • energy • wages

19. New Information for Learning Outcome 3 What else can be done to maximise productivity in the manufacture of ammonia? • An iron catalyst is used to increase the rate of reaction. It speeds up both the forward and backward reaction, so the position of equilibrium is not affected. • The ammonia is cooled, liquefied and then removed as it is produced. This causes the equilibrium to shift to the right to produce more ammonia. • Unreacted nitrogen and hydrogen are recycled and given another chance to react.

20. Create Evaluate Analyse Apply Understand Remember Demonstrate your Learning for Outcome 3 (A*) Explain the compromises in conditions that are made during the Haber process. (B) How would a low temperature and low pressure effect the amount of ammonia made in the Haber process? Understand (D) What is a catalyst and why is it used in the Haber process?