5.23   describe the manufacture of ammonia by the Haber process, including the essential conditions:

i     a temperature of about 450°C

ii    a pressure of about 200 atmospheres

iii   an iron catalyst

Key equation:

N2(g) + 3H2(g) ⇌ 2NH3(g)

More facts to learn!

Why does the Haber Process operate at 200 atm and 450 ºC?

High pressure is good. It increases the yield (as explained above), and also the rate. We don’t make the pressure higher still, because the increased cost of doing that is not worth the relatively low extra increase in yield and rate.

High temperature is bad for the yield (as explained above). However, we use a high temperature to get a reasonable rate. It is a compromise between yield and rate. There is no point in having a yield of 100 % if it takes all month to make one tonne of ammonia!  (This is why the catalyst is so useful. If we didn’t use a catalyst, the temperature would have to be higher still to get a reasonable rate, and the yield would be even lower).