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Making Ammonia
· Used to make fertilisers and
other chemicals
· Nitrogen and hydrogen are
purified and mixed
· Gases passed over an iron
catalyst at 450oC and 200
atmospheric pressures
· These conditions give fast rate
and reasonable yield…read more

Slide 3

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Making Ammonia
· nitrogen + hydrogen ammonia
· N2(g) + 3H2(g) 2NH3(g)
· Reaction is reversible
· Some ammonia produced breaks
down into hydrogen and nitrogen
again ­ yield only about 15%
· Unreacted gases are recycled so
not wasted…read more

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Temperature and Pressure

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Why is there an optimum
· Products have fewer molecules
of gas than reactants
· So higher pressure = greater
yield of ammonia
· Higher presusre ­ more energy
needed to compress the gas and
need stronger vessels
· 200 atmospheres is a
comprimise between cost and
yield…read more

Slide 6

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Why is there an optimum
· Forward reaction exothermic so
lower temperature the greater
the yield of ammonia
· However rate of reaction
decreases as temperature
lowered and iron catalyst =
· 4500C is a compromise between
yield and time…read more


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