Occurrence and Preparation of Ammonia

Ammonia is the most important compound of nitrogen. Its chemical formula is .

It is the starting material for the preparation of many other compounds of nitrogen.

Let us first find out how ammonia occurs in nature.

It is a chemical found in trace amounts in nature, produced by nitrogenous animal and vegetable matter.

Ammonia and some of its salts are also found in rainwater.

Moving on, let us look at how ammonia can be prepared.

In the earlier days, it was mostly prepared by treating urea with water and heating it

It can also be prepared by heating an ammonium salt with a strong alkali like either in solid or in the aqueous form.

Let us at go on to find out how ammonia is prepared industrially.

Generally, for industrial usage, ammonia is prepared by Haber’s process.

Chemical equation involving haber process is this:

In this process, first a mixture of nitrogen and hydrogen is taken in the ratio of 1:3.

It is then compressed to 200-900 atm with a compressor.

Then the compressed gas mixture is cooled and passed through a soda lime tower which absorbs moisture and carbon dioxide.

The gas mixture from the soda tower is passed over the catalyst maintained at 725-775K in an electrically heated chamber.

The gases coming out of the electrical chamber contain 10-20% of ammonia and they are cooled in a refrigerating column.

This residual mixture still contains nitrogen and hydrogen and it can be recirculated for the conversion into ammonia.

Let us now look at the favourable conditions for obtaining the maximum yield of ammonia.

On going from the reactant side to the product side, there is decrease in the number of moles.

This decrease in number of moles also indicates a decrease in volume.

As the volume decreases on the product side, increasing the pressure will move the reaction forward.

This is accordance with Le-chatelier's principle.

Also, since energy is released in the above reaction it is an exothermic reaction

So low temperature favours the forward reaction.The optimum temperature is 720-770K

In order to increase the rate of reaction, suitable catalyst is also required.Finely divided iron is used as a catalyst widely.

Nowadays, iron oxide mixed with small amounts of and are also used as a catalyst.

To support the catalyst in the reaction, substance called promoter is added.

In this haber process, molybdenum is used as a promoter to support iron (which is a catalyst).

So to conclude, the favourable conditions for the maximum yield of ammonia are: low temperature, high pressure and a catalyst.

And the optimum conditions are:

LET US RECALL WHAT WE HAVE LEARNT..

Ammonia is a very important compound of nitrogen with wide range of applications. It is earlier prepared from urea.

It can be prepared from other alkalis like caustic soda or calcium hydroxide.

But Ammonia is mainly prepared by Haber’s process. This reaction is favoured by low temperature and high pressure.

Fe is used as a catalyst and Mo is used as promoter.The output of the haber reaction is high when compared to other preparation methods

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