Chapter 10 - Ammonia Flashcards
What is ammonia industrially made by?
The Haber process
What are the raw materials in the Haber process?
Nitrogen and hydrogen
How is nitrogen gas obtained?
Fractional distillation of liquid air
How is hydrogen gas obtained?
The cracking of crude oil fractions
What is a reversible reaction?
A reaction that can go both forward and backward at the same time
Is the Haber process a reversible reaction?
Yes, the reaction is exothermic and the backward reaction is endothermic
How does the Haber process look like in terms of chemical equation?
N₂(g) + 3H₂(g) ⇌ 2NH₃(g)
In the Haber process: N₂(g) + 3H₂(g) ⇌ 2NH₃(g), which is the forward reaction and which is the backward reaction?
Forward reaction: N₂(g) + 3H₂(g) → 2NH₃(g)
Backward reaction: 2NH₃(g) → N₂(g) + 3H₂(g)
Because the Haber process is a reversible reaction, what could likely happen to the produced ammonia?
Some ammonia produced may break down and convert back to nitrogen and hydrogen
Can a forward reaction take place at room temperature? Why?
No, nitrogen gas is unreactive. A high pressure and a relative high temperature is required for the forward reaction to start between nitrogen and hydrogen
Why does the pressure and temperature have to be carefully controlled?
The reaction is reversible, and some of the ammonia produced may break down and decompose back into nitrogen and hydrogen. So if they are controlled, we can obtain as much ammonia at minimal cost
What is the effect of pressure on the yield of ammonia?
1) Higher pressure = higher yield + faster reaction
2) Maintaining a high pressure incurs a large cost as it requires expensive equipment and large amount of electricity
3) Hence, a compromise o 200 atm is used
What is the effect of temperature on the yield of ammonia?
1) A lower temperature leads = higher yield (reduces decomposition of ammonia)
2) However, lower temperature = slower reaction
3) Hence, a compromise of 450 degree celcius is used
What is the purpose of a caatalyst?
1) The reaction is slow despite usinf a releatively high remperature and high pressure
2) Hence an iron catalyse is added to speed up the reaction
Whata re teh 3 optimal condiions for the Hbaer process to produe the macimum yield of ammonia at minimum cost?
1) A pressure of 250 atm
2) A temperature of 450 degree celcius
3) Presence of a finely-divided iron catalyst
What is inside a Haber process plant?
1) Nitrofen and hydrogen gas are mixed in the ratio 1:3 by volume
2) The gas mixture is compressed to 250 atm
3) The compressed gases flow over the iron catalyst and are heated to 450 degree celcius + only about 15% of the mixture leaving the chamber is ammonia
4) A mixture of ammonia, nitrogen and hydrogen is obtained anc ooled
5) Ammonia gas condenses into a liquid + liquid is pumped into tanks and stored under pressure
6) The unreacted nitrogen and hydrogen are transferred back into the converter to be recycled
Why is ammonia important?
1) Ammonia is used to make fertilisers such as
- ammonium phosphate (NH4)3PO4
- ammoniuum nitrate NH4NO3
- ammonium sulfate (NH4)2SO4
