C15 - Using our resources (Part 2 - Haber Process and Fertilisers)

Question 1

Common use of ammonia

Answer 1

Makes nitrogen based fertilisers

Question 2

Equation for the haber process

Answer 2

nitrogen + hydrogen ⇌ ammonia
N₂ + 3H₂ ⇌ 2NH3

Question 3

Source for nitrogen for the haber process

Answer 3

Extracted from the air

Question 4

Source for hydrogen in the haber process

Answer 4

Reacting methane with steam

Question 5

Describe the steps in the haber process

Answer 5

• N₂ and H₂ put into reaction vessel
• They are passed over an iron catalyst at 450°c and 200 atmopsheres pressure
• Some formation of ammonia
• This is then cooled, liquefied and removed
• The unreacted N₂ and H₂ and recycled back into the reaction vessel

Question 6

Optimum conditions for the Haber process

Answer 6

Low temp - causes equilibira to shift in the right, exothermic direction producing more ammonia
High pressure - shift equilibria to side with fewer molecules, increasing yield of ammonia (more on left hand side than rhs)

Question 7

Why are 450c and 200 atmospheres chosen

Answer 7

• Conditions are a compromise - they allow a relatively high yield, relatively high rate of reaction and cheaper cost
• The chosen temperature and pressure are a compromise between rate and cost and a compromise between rate and yield

Question 8

Problems with the optimum conditions for the Haber process

Answer 8

Low temp - causes rate of reaction to be too slow + reduces effectiveness of iron catalyst

High pressure - high enercy cost to compress the gas and expensive to have a strong reaction vessel that can withstand high pressure

Question 9

What compounds do NPK Fertilisers contain

Answer 9

• Nitrogen compunds
• Phosphorus compounds
• Potassium compounds

Question 10

What is the main compound of nitrogen in NPKs and how is it produced

Answer 10

• Ammonium nitrate
• This is made bu using ammonia from the haber process to make nitric acid
• The nitric acid is then reacted with more ammonia to make ammounium nitrate

Question 11

What are the main compounds of potassium in NPKs and how is it produced

Answer 11

• Potassium chloride or potassium sulphate
• Both of these are mined from the ground without any further processing

Question 12

What happens when you treate phosphate rock with nitric acid

Answer 12

• It produces a mixture of phosphoric aicd and calcium nitrate
• The phosphoric acid is then neutralised with ammonia
• This produces ammonium phosphate

Question 13

What happens when you treate phosphate rock with sulfuric acid

Answer 13

• It produces a mixture of calcium phosphate and calcium sulphate
• This mixture is called single superphosphate

Question 14

What happens when you treate phosphate rock with sulfuric acid

Answer 14

• It produces triple superphosphate

Question 15

Compare the methods for making ammonium sulphate in a lab with the industrial process

Answer 15

• The industrial process is quicker and is a continuous processand it can produce lots of ammonium sulphate on a large scale
• The lab process is slower and is a batch process and it produces a small amount of ammonia at a time
• The industrial process is very dangerous as it uses concentrated nitric acid and gaseous ammonia which is very exothermic whereas the lab uses dilute solutions
• The lab process requires lots of heat energy input but in the industrial process, the energy fro evaporation is provided by the exothermic reaction earlier