Manufacturing Chemicals (Making Ammonia) – Revision Pack (C2)
The Haber Process:
The world’s food production is
dependent on nitrogen fertiliser.
These fertilisers are made from
ammonia, which is the product of
the Haber process. The word
equation for the Haber process is:
Nitrogen + Hydrogen  Ammonia
N2 + 3H2  2NH3
The optimum (best) conditions for the Haber process are as follows:
Condition
Iron Catalyst
Reasoning
Speeds up the rate of reaction (or
successful collisions; does NOT increase
the percentage yield.
o
Temperature of 450 C (quite low)
Higher temperatures increase the
reaction rate, BUT also break down the
ammonia, reducing the percentage
yield.
High Pressure of 200atm
Higher pressure directly results in a higher
percentage yield.
Any unreacted hydrogen or nitrogen is recycled and used again.
The optimum temperature is 450oC – this is quite low for an industrial process but is
‘the best of a bad balance’ because while the percentage yield suffers, the rate of
reaction is very high. It is a compromise.
What affects the cost of chemical manufacturing?
Any chemical plant (where the chemicals are made) is NOT looking for the highest
yield, but the most economic yield.
Costs will increase when more energy is used, or when the temperature is increased.
This is why the temperature is kept quite low in the Haber process. If you increase the
amount of pressure you use, you will increase the plant costs.
Manufacturing Chemicals (Making Ammonia) – Revision Pack (C2)
Cost is decreased when you use an iron catalyst and recycle unreacted starting
materials.
Automation is used to keep wage costs low; you don’t have to pay workers to do it,
because it is all automated.
These factors are all taken into consideration for the Haber process:
-
The temperature and pressure must be high enough to give a sufficient daily
yield
A low percentage yield can be accepted if the products can be recycled
and the reaction repeated many times
The optimum temperatures used for the Haber process do NOT ensure that we get
the highest percentage yield or rate of reaction, but actually give the lowest cost
and as such, the most profit.
Manufacturing Chemicals (Making Ammonia) – Revision Pack (C2)
Past Papers:
PPQ(1):
Manufacturing Chemicals (Making Ammonia) – Revision Pack (C2)
PPQ(2):
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Manufacturing Chemicals (Making Ammonia) – Revision Pack (C2)
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PPQ(4):
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Manufacturing Chemicals (Making Ammonia) – Revision Pack (C2)
Manufacturing Chemicals (Making Ammonia) – Revision Pack (C2)
Mark Schemes:
PPQ(1):
PPQ(2):
PPQ(3):
Manufacturing Chemicals (Making Ammonia) – Revision Pack (C2)
PPQ(4):
PPQ(5):