Haber Process and use of NPK Fertilisers (10.4) (M) Flashcards
What can the Haber process be used to do?
manufacture ammonia
What can ammonia be used to do?
to produce nitrogen-based fertilisers
What are the raw materials for the Haber process?
nitrogen and hydrogen
What is a source of nitrogen?
air
What is a source of hydrogen?
By reacting natural gas (methane normally) with steam
What happens to hydrogen and nitrogen in the Haber process to manufacture ammonia?
The purified gases are passed over a catalyst of iron at a high temperature (about 450°C) and a high pressure (about 200 atmospheres)
What is type of reaction is the one in the hater process?
a reversible reaction
What is the equation for the Haber process?
The Haber process is reversible, what does this mean?
Only some of the hydrogen and nitrogen reacts to form ammonia.
Some of the ammonia produced breaks down into nitrogen and hydrogen
How is ammonia collected after being produced?
It is cooled, the ammonia liquefies and is removed
What happens to the hydrogen and nitrogen in the Haber process that don’t react?
They are recycled
to save money and increase effective overall yield
In the Haber process, the forward reaction is (…) and the backward reaction is (…)
exothermic
endothermic
Why is iron used in the Haber process?
Iron is a catalyst for the reaction.
It increases the rate of the reaction without being used up in the reaction (what a catalyst does)
Doesn’t change equilibrium position
What is the problem with using very high pressures (and temperatures) in the Haber process?
expensive and dangerous
Explain how the commercially used conditions for the Haber process are related to the availability and cost of raw materials and energy supplies
You need to use natural gas to heat the reaction and to get the hydrogen. If the price of these goes up, the cost of fertiliser increases
if in low availability, the price will be high
Compounds containing what are used in an NPK fertiliser?
(the elements) nitrogen, phosphorus and potassium
Why are (NPK) fertilisers used?
to improve agricultural productivity
fertilisers provide mineral ions for healthy growth
What do nitrogen, phosphorus and potassium each provide as a fertiliser to plants?
N - healthy foliage (leaves)
P - strong roots
K - healthy growth
What are NPK fertilisers?
formulations of various salts containing appropriate percentages of the elements nitrogen, phosphorus and potassium
How can industrial production of NPK fertilisers be achieved?
using a variety of raw materials in several integrated processes
What can ammonia can be used to manufacture? (not nitrogen-based fertiliser answer, this is a chemical one)
ammonium salts and nitric acid
How can potassium chloride, potassium sulfate and phosphate rock be obtained?
by mining
Phosphate rock is insoluble in water and so cannot be taken up by plants, what does this mean?
phosphate rock cannot be used directly as a fertiliser
so must be converted into salts (which are soluble)
How is phosphate rock treated for use in fertilisers?
Phosphate rock is treated with nitric acid or sulfuric acid to produce soluble salts that can be used as fertilisers
What is the salt produced when phosphate rock is treated with nitric acid?
Calcium nitrate (which can be used as a fertiliser) and phosphoric acid, the latter is neutralised with ammonia to make ammonium phosphate
What is the salt produced when phosphate rock is treated with sulfuric acid?
Single superphosphate, which is a mixture of calcium sulfate and calcium phosphate
What is the salt produced when phosphate rock is treated with phosphoric acid?
Triple superphosphate (calcium phosphate)
How are fertilisers produced in the lab?
Do neutralisation one time with indicator
Do it without indicator second time
Evaporate gently
This is small scale and takes a short time - easier to do
How are fertilisers produced in industrial processes?
Large scale production
Starts with raw materials - cheaper than buying in ammonia and acid or other compounds
It is a continuous process - keep adding raw materials as is cheaper to do so
Why has the demand for ammonia has increased?
The world population has increased
So demand for fertiliser (for producing food) has increased
What is the purpose of pipe x?
to recycle unreacted hydrogen and nitrogen
Key exam technique - 6 points
Suggest and explain why the conditions used to produce ammonia in the Haber process are a temperature of 450 °C and a pressure of 200 atmospheres
reaction is reversible
forward reaction is exothermic so increased temperature lowers the yield of ammonia
a lower temperature would decrease rate of reaction, so that the reaction is too slow
a higher pressure would increase the yield of ammonia because the forward reaction produces the least number of (gaseous) molecules / moles
higher pressures would involve high cost / energy
450oC gives a reasonable yield at a fast rate
2 marker
Why is a temp of 450oC used in the haber process?
A higher temperature would reduce the yield
A lower temperature would reduce the rate of reaction
Why would showing a ratio label of elements in an NPK fertiliser be useful to the farmer?
shows fertilisers are formulations
so farmer can choose fertiliser with required properties
2 marks
Why would the haber process cause the closure of mines?
Ammonia/Haber process can be used to make a fertiliser
raw materials for haber process are readily available or haber process is continuous or transport costs are lower
What are the three salts/materials that can be obtained by mining?
- potassium chloride
- potassium sulfate
- phosphate rock
