The Haber Process Worksheet printable pdf download

C h e m g u i d e – a n s w e r s

THE HABER PROCESS

1. a) 1 volume of nitrogen to 3 volumes of hydrogen (or: in the ratio of 1 mole of nitrogen to 3 of

hydrogen; or: in equation proportions)

b) 400 - 450°C

c) 200 atmospheres (in fact, anything from this up to about 1000 atm would be OK)

d) iron

e) The equilibrium mixture of gases is cooled. Because of the very high pressures, the ammonia

turns to liquid and can be separated from the unreacted gases which can be recycled.

2. a) the choice of temperature:

Equilibrium: The production of ammonia is exothermic:

According to Le Chatelier, if you lower the temperature the system would react by countering this

by favouring the exothermic change. That means that a low temperature would give a higher

percentage conversion into ammonia.

Rates: At a low temperature, the formation of ammonia is very slow (or even non-existent).

Increasing the temperature increases the rate at which equilibrium is reached. However, a high

temperature means a low percentage yield of ammonia.

Economics: There are no extra factors to consider here. The temperature is chosen as a

compromise to give the best possible yield of ammonia reasonably quickly.

b) the choice of pressure:

Equilibrium: A high pressure favours the reaction which produces fewer molecules. Fewer

molecules produce a lower pressure. This is consistent with Le Chatelier's Principle – countering

the change you have made. So in this case, to get the maximum percentage conversion to ammonia

you would choose a very high pressure.

Rates: High pressures bring molecules closer together and so increase collision rates , increasing

the rate of reaction.

Economics: Very high pressures are expensive to produce. They need very strong pipes and

containment vessels, and lots of energy to generate. The pressures actually used are a compromise

on economic grounds.

The Haber Process Worksheet