The Haber process - choosing a temperature

A compromise temperature

The forward reaction in the Haber process is exothermic [exothermic: Heat energy is released in an exothermic reaction. We know this because the surroundings get warm. ]. This means that if the temperature is increased, the position of equilibrium moves in the direction of the reverse reaction, and less ammonia is formed.

The effect of varying the temperature in the Haber process

You might think that a low temperature would be a good choice for the Haber process: if the forward reaction is exothermic, the yield of product at equilibrium [equilibrium: If the rate of the forward reaction and the rate of the back reaction in a reversible reaction are equal, the reaction is in equilibrium. ] is increased at lower temperatures. However, if the temperature is too low the rate of reaction will be too low. This would make the process uneconomical. So a compromise temperature is chosen: low enough to get a good yield of ammonia but high enough to obtain a reasonable rate of reaction.

An iron catalyst

The presence of a catalyst [catalyst: A catalyst changes the rate of a chemical reaction without being changed by the reaction itself. ] does not affect the position of the equilibrium, but it does increase the rate of the reaction. This means the ammonia is produced in a shorter time, reducing the cost of the process. Iron is a cheap catalyst.