The haber process + fertilisers Flashcards
What is ammonia made up of?
NH3
Ammonia uses
Nitrogen based fertilisers
How can we produce ammonia?
The Haber process
Haber process equation
N₂ + 3H₂ <——> 2NH₃
Where do we get nitrogen for the haber process?
Extracted from the air
Where do we get hydrogen for the haber process from?
Product of reacting methane with steam
Conditions for haber process
Iron catalyst
450ºC
200 atm pressure
Process of the haber process
Pass purified nitrogen + hydrogen over the iron catalyst
At 450°C and 200 atm
Thus molecules react and form ammonia
But because it’s reversible some of it breaks back down to N and H
Which is recycled again over catalyst
Ammonia then cooled to turn it back to liquid so it’s removed
Why do we cool the ammonia produced back to liquid?
To increase the yield
Why would we decrease the temperature of the haber process?
Foreword reaction is exothermic
So via Le chatelier’s principle, decreasing the temperature will shift the equilibrium forward
Thus causing a higher yield of ammonia
But why would we increase the temperature of the haber process?
A low temperature means low rate of reaction
Because the molecules have less thermal energy which can be transferred to kinetic energy
So with less movement means less successful collisions per second
Which isnt economical as it produces ammonia too slow = paying more for fuel costs
How do we decide the temperature for the haber process?
Can’t have too low of a temp as that causes a slow rate of reaction that isn’t economical
Can’t have too high temp as it decreases the yield of ammonia
Also high temperature is a higher fuel cost
450°c = compromise temperature
Why would we increase the pressure of the process?
High pressure causes equilibrium to shift to the side with less particles which is the forewords reaction
So increasing pressure causes increase in ammonia yield
Also a higher pressure causes higher rate of reaction as there are more particles in a given volume
So more successful collisions per second
Why would we decrease the pressure of the reaction?
Having gases at a very high pressure is expensive and dangerous
As it requires extra cost for specialist equipment to keep it at this level
How do we decide the pressure of the haber process?
Can’t be too low as with a high pressure, it will increase the yield as equilibrium shifts forward
Also causes higher rate as more particles in a given volume
Can’t be too high as that’s expensive and dangerous
200atm is a good compromise
Iron catalyst usage
Provides alternative reaction pathway
Lowers activation energy
So when particles collide they don’t need to collide with as much energy
Thus increases the number of successful collisions
Therefore higher rate of reaction
How does the iron catalyst effect equilibrium?
It does not
It only increases the rate of reaction
As the activation energy is lower
Use of fertilisers
Replace elements used as minerals for plants that get taken up by plants
So plants grow larger and rapidly
So improve agricultural productivity
NPK fertiliser
Fertiliser containing a formulation of salt compounds of:
Nitrogen
Phosphorus
Potassium
The salts containing these elements, not the elements on their own
Where do we produce NPK fertilisers?
Industrial facilities that process RAW MATERIALS
Compounds of nitrogen in NPK fertilisers
Ammonium nitrate NH₄NO₃
Made from ammonia (haber process) to make nitric acid
React this nitric acid with more ammonia to make it
How do we get the compounds of phosphorus in NPK fertilisers?
From phosphate rocks and acids that are chemically processed after mining them
This can happen in many different ways
Names of phosphoric compounds in NPK fertilisers
Ammonium phosphate
Mixture of calcium phosphate and calcium sulphate (single superphosphate)
Calcium phosphate (triple superphosphate)
Phosphate rock processing with nitric acid to get ammonium phosphate
Phosphate rock + nitric acid ——> PHOSPHORIC ACID + calcium nitrate
We take this phosphoric acid and:
Phosphoric acid + ammonia ——> ammonium phosphate
Use this in NPK fertiliser
Why do we react phosphoric acid with ammonia?
Because although phosphoric acid contains phosphorus
We can’t add it directly to plants
So we NEUTRALISE IT with ammonia
Phosphate rock processing with sulfuric acid
Phosphate rock + sulfuric acid ——> calcium phosphate + calcium sulfate
The mixture of the products is called single superphosphate
Phosphate rock treated with phosphoric acid
Phosphate rock + phosphoric acid ——> calcium phosphate
Aka triple superphosphate
Compounds of potassium in NPK fertilisers
From the salts:
Potassium chloride
Potassium sulfate
Mined from the ground
With no further processing
Why do we need nitrogen in NPK fertilisers?
To help leaves or the plants
Why do we need phosphorus in NPK fertilisers?
To help root growth of the plants
Why do we need potassium in NPK fertilisers?
Growth of plant
For the fruits and flowers
How is the Haber process linked with NPK fertilisers
Haber process = Production of ammonia
Allows us to make nitric acid
And react that with more ammonia
To make ammonium nitrate for the nitrogen in the fertiliser
Allow us to process phosphate rock with ammonia to make ammonium phosphate for the phosphorus in the fertiliser
Ammonium nitrate production
Ammonia + nitric acid ——> ammonium nitrate
A salt so we have crystals
Producing ammonium nitrate in a school lab
Dilute solutions of ammonia and nitric acid —> salt crystals
Safe to work with
React these together, place over a water bath that’s above a Bunsen burner to evaporate requiring heat energy
Only makes small amounts in one go = a batch process
Producing ammonium nitrate in industry
Ammonia gas + concentrated nitric acid
This is dangerous as the reaction is very exothermic
=releases a lot of heat energy
This energy safely removed to be used later
In order to evaporate this product into the salts
A continuous process making large amounts
