Balancing equations – the Haber process –
The reaction between nitrogen and hydrogen to produce ammonia
Pre-story: Three hydrogen molecules and one nitrogen molecule are needed (eight students) holding ‘bonds’
to join them and band hats to identify them as H or N atoms. Students need to practise having the right
number of pieces of paper to make new bonds in the product molecules. For the freeze frame at the end, a
further three hydrogen and one nitrogen molecules are needed (eight more students with hats and bonds).
Narrator
Hydrogen and nitrogen molecules are mingling with one another in a big, steel container.
Action: Molecules swirl around each other gently, occasionally bumping into one another but just bouncing
off.
Narrator
The chemical engineer turns up the heat and turns up the pressure.
Action: A student wearing a lab coat and safety goggles on comes along and waves the flame and pressure
gauge at the molecules in a dramatic fashion.
Narrator
Molecules of ammonia are produced slowly, which float off (or if the pressure is great
enough settle down as a liquid).
Action: Hydrogen molecules ‘break bonds’ – one H holds on to piece of paper; nitrogen molecules ‘break
bonds’ – one N holds on to piece of paper; three H atoms join to one N atom on opposite sides, making sure
a piece of paper is there for each new N–H ‘bond’ (more paper is needed). There will be two new NH3
molecules made.
Freeze frame
Narrator
Here is the balanced equation for the reaction between hydrogen and nitrogen.
Action: The extra three hydrogen molecules and one nitrogen molecule line up to the left of the two
ammonia molecules. Another student holds the large arrow in between reactants and product molecules
pointing from left to right.
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© Ian Abrahams and Martin Braund (2012) Performing Science. London: Continuum.