Transcript Syllabus/Unit: code: C2 Chemical Resources Lesson number

Syllabus/Unit: code: C2 Chemical Resources
Lesson number: 5
Lesson Title: Manufacturing Chemicals - Ammonia
Learning Outcomes
Learning Outcome 1:
Describe how ammonia is made and some
of its uses
Grade C
Learning Outcome 2:
Interpret data about percentage yield in
reversible reactions and changes in
conditions
Grade B
Learning Outcome 3:
Explain the conditions in the Haber
Process and how factors including
economic ones affect their choice
Grade A/A*
How I did
Targets
Connector:
List factors that
would affect the
making of a new
substance
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Keywords:
•
•
•
•
Reversible reaction
Fertiliser
Yield
Catalyst
Put your hand up if there is any key word from the
list that you don’t know the meaning of.
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New Information for Learning Outcome 1
Factor
How it affects the cost
Cost of starting material
Complex machinery and high
pressure increase costs
Cost of equipment needed
Gas and electricity are expensive.
High temperatures also increases
energy costs
Labour costs and wages
Different starting materials cost
different amounts. Costs reduced if
unreacted materials are recycled
Price of the energy needed
Catalysts increase the rate of
chemical reactions and reduces costs
Speed at which new substance is
made
More workers there are, the greater
the costs. Costs may be reduced if
process are automated
(robots/computers)
New Information for Learning Outcomes
Haber Process Task
Research and collect information about the Haber process, include:
1. What is the Haber process – what is it used to make? Include a word
equation and a balanced symbol equation.
2. Who invented the Haber process?
3. The product made in the Haber process – what things is it used for?
4. What conditions are needed for the Haber process to take place:
• What does the temperature need to be?
• What catalyst is needed for the reaction to happen?
• What pressure is needed for the reactions?
5. The Haber process is a reversible reaction, what do we mean by this?
6. Why is a higher or lower temperature or a higher or lower pressure than
those identified in part 4. used in the reaction?
New Information for Learning Outcomes
It is made industrially by reacting nitrogen with
hydrogen in the Haber process. It is a reversible
reaction, so it never goes to completion.
nitrogen
+
hydrogen
ammonia
N2 (g)
+
3H2 (g)
2NH3 (g)
The hydrogen comes from cracking oil fractions or
from natural gas. The nitrogen comes from air.
As nitrogen is relatively unreactive, certain
conditions are needed to make sure it reacts with
nitrogen:
• High pressure
• Temperature around 450°C
• Adding an iron catalyst to speed up the reaction.
Recycling
unreacted H2 and
N2 helps reduce
costs too!
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New Information for Learning Outcomes
• Ammonia is one of the most important substances
than humans make.
• Over 140 million tonnes a year are made.
• What are some of the uses?
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•Ammonia is often
used in cleaning
products because it
reacts with grease
making this easier
to remove
Ammonia has other uses
including hair dyes
•Ammonia and nitric acid react together to produce
ammonium nitrate which makes artificial fertiliser
•Fertilisers are
substances applied to the
soil to replace the
minerals plants use
•Fertilisers are so important
to food production they use
80% of all ammonia
manufactured
New Information for Learning Outcome 2
Reversible reactions occur when the backwards reaction (products 
reactants) takes place relatively easily under certain conditions. The
products turn back into the reactants.
A
+
B
(reactants)
C
+
D
(products)
For example, during a reversible reaction reactants A and B react to
make products C and D.
However, products C and D can also undergo the reverse reaction,
and react together to form reactants A and B.
New Information for Learning Outcome 2
nitrogen
+
hydrogen
ammonia
N2 (g)
+
3H2 (g)
2NH3 (g)
Conditions for the Haber process have to be carefully chosen to
make sure that forward reaction is favoured.
This will make sure we get the biggest yield possible (the amount
of substance made in a reaction).
ammonia yield (%)
The yield of ammonia produced by the Haber process depends on the
temperature and pressure of the reaction.
pressure (atm)
Keywords:
Demonstrate your
Learning for Outcome 2
Create
Evaluate
Analyse (B)
Analyse
Apply (C)
Apply
Why are a high pressure and
450°C temperature chosen for
the Haber process?
From the graph, what is
the yield of ammonia at:
a. 100 atm. and 400°C
Understand
Remember (E)
b. 400 atm. and 550°C
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Remember
What does the term ‘yield’
mean?
New Information for Learning Outcome 3
The highest yield of ammonia is
theoretically produced by using a
low temperature and a high
pressure.
In practice, though, these conditions
are not used. Why?
Lowering the temperature slows down the rate of reaction. This means
it takes longer for ammonia to be produced.
Increasing the pressure means stronger, more expensive equipment is
needed. This increases the cost of producing the ammonia.
A compromise is reached to make an acceptable yield in a
reasonable timeframe while keeping costs down.
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New Information for Learning Outcome 3
To produce a high yield of ammonia, but with a fast rate of reaction
and without the need for overly expensive equipment, the Haber
process is carried out at 450 °C and 200 atmospheres.
The most important factor in deciding
what conditions to use is therefore not
yield, but total cost.
What costs are involved in the
industrial production of ammonia?
 raw materials
 equipment
 energy
 wages
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New Information for Learning Outcome 3
What else can be done to maximise productivity in the manufacture of
ammonia?
 An iron catalyst is used to increase the rate of reaction. It speeds
up both the forward and backward reaction, so the position of
equilibrium is not affected.
 The ammonia is cooled, liquefied and then removed as it is
produced. This causes the equilibrium to shift to the right to
produce more ammonia.
 Unreacted nitrogen and hydrogen are recycled and given another
chance to react.
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Demonstrate your
Learning for Outcome 3
Create
Evaluate
(B)
How would a low
temperature and low
pressure effect the
amount of ammonia
made in the Haber
process?
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(A*)
Explain the compromises in
conditions that are made
during the Haber process.
Analyse
Apply
Understand
Understand (D)
Remember
What is a catalyst and why is
it used in the Haber
process?