Ammonia is an important chemical used worldwide in products such as fertilisers and dyes. But how do we produce ammonia? We use an industrial method called the Haber process. Named after its inventor Fritz Haber and Carl Bosch in the 20th century, it is a complex process involving the reversible reaction of nitrogen and hydrogen under specific conditions.
- Firstly, we shall find out what the Haber process is and look at its main stages.
- Then, we shall explore a Haber process diagram to visualise the stages.
- After that, we shall look at the Haber process equation and how this relates to equilibrium.
- Finally, we will explore the conditions of the Haber process and the compromises made.
What Is The Haber Process?
The Haber process is a process carried out in order to manufacture ammonia. Ammonia is manufactured because it is used to produce fertilisers that are nitrogen-based.
The Haber process requires two key raw materials in order to be carried out - hydrogen and nitrogen. Nitrogen can be obtained from the air and hydrogen can be obtained from natural gas and other sources.
Fig. 1: Ammonia structure.
Stages Of The Haber Process
- The hydrogen and nitrogen are pumped into a compressor with the use of pipes.
- The hydrogen and nitrogen mixture is compressed inside the compressor at a pressure of 200 atm (atmospheres) and a temperature of 450 degrees Celsius.
- The gases are pumped into a reaction vessel that contains an iron catalyst.
- The gases are cooled in the cooling tank and the ammonia is liquified and left to separate/be removed.
- The unreacted nitrogen and hydrogen are recycled by returning back to the reaction vessel so that they are not wasted.
Fig. 2: This diagram above illustrates the stages of the Haber process as explained.
Haber Process Diagram
Here's a visual summary of the Haber process:
In the following sections, we will look at the conditions of the Haber process and explain each step in more detail.
The Haber Process Conditions
The conditions of the Haber process are:
• An iron catalyst.
• Temperature of 450 degrees Celsius.
• Pressure of 200 atmospheres.
All these conditions are compromised to produce a fair amount of yield with a reasonable cost and time.
The Temperature of the Haber Process
The temperature used for the Haber process as outlined is 450 degrees Celsius. The forward reaction is exothermic so if the temperature is lowered then the yield of ammonia would increase, however, the rate of reaction would decrease meaning that the reaction will be slow.
On the other hand, if a higher temperature is used then the yield of ammonia would decrease and the yield of reactants would increase which is not the objective of this process. Therefore, a temperature of 450 degrees Celsius is used as a compromise.
Pressure during the Haber Process
The pressure used for the Haber process is approximately 200 atmospheres. If the pressure is increased then this leads to an increase in the yield of ammonia as there are fewer molecules on the right-hand side of the equation (product side).
However, If a lower pressure is used then the yield of reactants increases as there are more molecules on the left-hand side of the equation. High pressures are very expensive due to the high costs of energy and can be dangerous. Therefore, a pressure of 200 atmospheres is a compromise where the yield of ammonia being produced is low but is produced safely.
Catalyst in the Haber Process
The catalyst used in the Haber process is an iron catalyst. The position of the equilibrium is not affected by the catalyst but the rate of reaction is. A catalyst can be used to increase the rate of reaction as it lowers the activation energy by providing an alternative pathway.
The use of a catalyst also allows for a lower temperature to be used so that a reasonable amount of yield is produced. If a catalyst wasn't used then the reaction would have been carried out at higher temperatures. This would lead to a higher cost and less production of the yield.
The Haber Process Equation And Equilibrium
When ammonia is produced by the reaction between hydrogen and nitrogen, the reaction is said to be reversible. This means ammonia can be converted back into nitrogen and hydrogen. The symbol used for the term "reversible" in chemistry is ⇌.
The word equation for this reaction is:
The symbol equation for this reaction is:
This reaction leads to dynamic equilibrium because of the forward and backward reactions occurring continuously. The position of the equilibrium is affected by a number of factors such as temperature and pressure. For example, if the pressure increases then the yield of ammonia also increases at any given temperature.
However, the actual conditions used are chosen according to the different considerations such as cost, availability, and supplies of raw materials. Companies in this industry have to consider the costs of extraction of raw materials and the costs of the production of energy in order to make sure the process is practicable.
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