The haber process Flashcards
What does the Haber process produce?
Ammonia (NH3).
What is ammonia used to make?
Fertilisers.
What is needed to make ammonia?
- Nitrogen.
- Hydrogen.
What is the reaction for making ammonia?
N2(g) + 3H2(g) ⇌ 2NH3 (g)
Where do we get the nitrogen from that we use to make ammonia?
It is obtained easily from the air, which is 78% nitrogen and 21% oxygen.
Where do we get the hydrogen from that we use to make ammonia?
It comes from natural gas or from other sources like crude oil.
What does it mean that the reaction to make ammonia is reversible?
That it occurs in both directions, so ammonia breaks down again into nitrogen and hydrogen, and the reaction reaches equilibrium.
What are the industrial conditions needed to make ammonia?
- Pressure: 200 atmospheres.
- Temperature: 450’c.
- Catalyst: Iron.
Because the reaction is reversible, what is there to be made?
A compromise.
To get more product what do we do?
Increase the pressure, as higher pressures favour the forward reaction.
Why do higher pressures favour the forward reaction?
As for every four molecules of gas on the left-hand side, there are two molecules on the right hand side.
Why is the pressure set as high as possible, but not too high?
To get the best percentage yield, without making the plant too expensive to build (we use 200 atmospheres pressure).
What type of reaction is the forward reaction?
Exothermic.
What does it mean that the forward reaction is exothermic?
That increasing the temperature will move the equilibrium the wrong way, away from ammonia towards N2 and H2.
When is the yield of ammonia greater?
At lower temperatures.
What do lower temperatures mean?
That a lower rate of reaction would occu.
Why do they increase the temperature, even though the yield will be lower?
To get a much faster rate of reaction.
What is the temperature of 450’c?
A compromise between maximum yield and speed of reaction.
What is it better to do when making ammonia, which is why we increase the temperature to increase the rate of reaction?
Wait 20 seconds for a 10% yield than 60 seconds for a 20% yield.
How is the ammonia formed in the Haber process?
As a gas, but as it cools in the condenser it liquefies and is removed.
What is good about the Haber process?
Nothing is wasted.
How is nothing wasted in the Haber process?
The unused hydrogen (H2) and nitrogen (N2) are recycled.
What does the iron catalyst do?
- It makes the reaction go faster, which gets it o the equilibrium proportions more quickly.
- It keeps costs down.
What would happen without the iron catalyst?
The temperature would have to be raised even further to get a quick enough reaction, which would reduce the percentage yield even further.
