Haber Process HQ

Making ammonia from air

The Haber process makes ammonia, a gas the world needs to make fertilisers that feed crops. The two raw materials are cheap and plentiful: nitrogen comes from the air and hydrogen comes from natural gas. They are combined in the reaction N2 plus 3H2 gives 2NH3. This reaction is reversible, so the ammonia can break back down, and only some of the gases combine each time. To get a good amount at a sensible speed, industry uses a high pressure, a temperature of around 450 degrees Celsius and an iron catalyst. As you will see, that temperature is a careful compromise between how fast the reaction goes and how much ammonia it makes. This module explains the process and those conditions.

Haber words

Learn these before you match any condition, and remember the reaction can run both ways.

Rate against yield

The temperature choice is a tug of war, because what helps the speed hurts the amount made. The forward reaction is exothermic.

How to explain the compromise

For a top answer, take each condition and say what it does to two things: the speed and the amount made. High pressure and the iron catalyst are easy, since both help without a downside worth worrying about. Temperature is the clever bit. Around 450 degrees Celsius is chosen not because it is best for either alone, but because a cooler run would crawl and a hotter run would waste the ammonia. Name the winner for each and justify the middle ground.

Match the condition to why it is used

Where do the raw gases come from?

A factory needs the two raw gases to run the Haber process. Where does the hydrogen come from?

• From natural gas.
• From the air.
• From limestone.
• From iron ore.

Conditions in the Haber process

Select the TWO conditions actually used in the Haber process.

• A high pressure
• An iron catalyst
• No catalyst at all
• A very low pressure

Hydrogen needed

In the reaction N2 plus 3H2 gives 2NH3, nitrogen and hydrogen react in the ratio 1 to 3 by volume. To react fully with 2 units of nitrogen, how many units of hydrogen are needed?

Order the Haber process

Put the stages of the Haber process in order, earliest first.

• Nitrogen from the air and hydrogen from natural gas are obtained
• The gases pass over an iron catalyst at high pressure and about 450 degrees Celsius
• Some of the gases combine to form ammonia
• The ammonia is removed and the unreacted gases are recycled

Complete the facts

The Haber process makes the gas _____, written NH3. Its nitrogen is taken from the _____ and its hydrogen from natural gas. Because the reaction can run in both directions it is described as _____. The reaction is sped up by an iron _____.

Match the part to its role

Spot the true Haber facts

Tap the TWO statements that are true about the Haber process.

• The reaction that makes ammonia is reversible
• An iron catalyst speeds the reaction up
• The nitrogen is taken from natural gas
• The temperature is set only for the highest yield

Judge the conditions

Read each case and choose the best response, with a reason.

• A factory owner suggests running much cooler to raise the ammonia yield. What is the honest drawback of a much lower temperature?
• An engineer asks why an iron catalyst is added. What is the best reason?
• A student writes that 450 degrees Celsius simply gives the highest yield. How should the answer be corrected?

Explain the Haber conditions

A company runs the Haber process to make ammonia. Explain the conditions it uses and why the temperature is a compromise.

• Name the raw materials and where nitrogen and hydrogen come from
• State that the reaction is reversible
• Explain what the high pressure and the iron catalyst do
• Explain why a lower temperature would raise yield but is not used
• Finish with a judgement on why around 450 degrees Celsius is chosen