C3.5 The Haber process and yield

Question 1

What is ammonia?

Answer 1

A compound of nitrogen and hydrogen (NH3)

• Colourless
• Strong smell
• Weak alkali

Question 2

What can ammonia be used for?

Answer 2

• Plant fertilisers (nitrogen = energy)
• Explosives
• Dyes
• Nylon
• Nitric acid production

Question 3

What materials are needed for the Haber process?

Answer 3

Hydrogen and nitrogen

Question 4

Is the reaction to produce ammonia reversible?

Answer 4

yes

N2(g) + 3H2(g) (Equilibrium symbol) 2NH3(g)

Question 5

What are the conditions needed for the Haber process?

Answer 5

• High temp (abt 450)
• High pressure (200 atmos)
• Iron as catalyst

Question 6

What are the stages of the Haber process?

Answer 6

• Hydrogen and nitrogen are pumped into the compressor through pipes.
• The gases are pressurised to about 200 atmospheres of pressure inside the compressor.
• The pressurised gases are pumped into a tank containing beds of iron catalyst at about 450°C. In these conditions, some of the hydrogen and nitrogen will react to form ammonia.
• The unreacted nitrogen and hydrogen, together with the ammonia, pass into a cooling tank. The cooling tank liquefies the ammonia, which can be removed into pressurised storage vessels
• The unreacted hydrogen and nitrogen gases are recycled by being fed back through pipes to pass through the hot iron catalyst beds again.

Question 7

How does a changing pressure affect the yield of ammonia?

Answer 7

If the pressure is increased, the reactants that produce the least number of gas molecules is favoured

In the haber process, this means the reation producing ammonia is favoured

Question 8

How does temperature affect the yield of ammonia?

Answer 8

If the temperature is increased, the yield from the endothermic reaction is INCREASED
If the temperature is decreased, the yield from the endothermic reaction is DECREASED

In the Haber process, the temperature is decreased which favours the exothermic production of ammonia

Question 9

Why is the pressure used in the Haber process not higher than 200 atmospheres?

Answer 9

Achieving a high pressure requires a lot of energy which is expensive, also tough pipes are also required
200 atmospheres is the optimum pressure that is cost effective and also efficient

Question 10

Why is 450 degrees celcius the optimum temperature?

Answer 10

The temperature needs to be able to compensate the activation energy required to begin the reaction
It cannot be too low or the rate of reaction will be too slow to be efficient

Question 11

What does a company need to consider when producing ammonia, eg what conditions, temperatures,pressures ?

Answer 11

• The cost to produce the energy and pressure required
• The disposal of unused reactants (raw materials are recycled)
• The length of the process is costly (catalysts are used to speed it up)