Ostwald Process

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The Ostwald process is considered as one of the most chemical processes or common methods used for the manufacturing of nitric acid. The process of ostwald was developed in the year 1902 by a German chemist named Wilhelm Ostwald. In 1909 He was later awarded with the nobel prize for his research.

Over the years this process has gained popularity as it is the easiest way to produce nitric acid which is also widely used in many areas such as in the production of fertilizers as well as inorganic and organic nitrates or nitro compounds.

In the Ostwald process, Usually ammonia is transformed into nitric acid. Vanadium pentoxide which is denoted by V2O5 is often used as a catalyst during the processing of nitric acid in this method. There are many steps involved in this process. We shall discuss them.

The Ostwald process is defined as a chemical process used for making nitric acid which is written as HNO3. Wilhelm Ostwald developed this process, and inj 1902 he patented it. This process is a mainstay of the modern chemical industry, and it also provides the main raw material for the most common type of fertilizer production in the world. If we look at it historically and practically, then we can see that this process is closely associated with the Haber process, which provides the requisite raw material, ammonia.

Description of the Process

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The process is divided into two stages:

Stage 1

In this stage Ammonia is converted to nitric acid in 2 particular stages. By heating it is oxidized with oxygen in the presence of a catalyst such as platinum with 10% rhodium, on fuses the platinum metal on silica wool, copper or nickel, to form nitric oxide(nitrogen(II) oxide and water as steam. This reaction is considered as strongly exothermic process, making it a useful heat source once initiated:

4NH3(g) + 5O2(g) -> 4NO(g) + 6H2O (g)

ΔH = −905.2 kJ/mol

Stage 2

In this Stage two there encompasses two reactions and is carried out in an absorption apparatus which is containing water. Nitric oxide is oxidized initially again to yield nitrogen dioxide which is nitrogen(IV) oxide.This gas is readily absorbed then by the water, by yielding the desired product nitric acid, albeit in a dilute form, while reducing a portion of it back to nitric oxide as shown below:

2NO(g) + O2(g) -> 2NO2(g)

ΔH = −114 kJ/mol

3NO2(g) + H2O(l) -> 2HNO3(aq) + NO(g)

ΔH = −117 kJ/mol

The NO or nitric oxide is recycled, and the acid is concentrated to the required strength by distillation process.

If the last step is Alternatively carried out in air:

4 NO2(g) + O2(g) + 2H2O(l) -> 4HNO3(aq)

 ΔH = −348 kJ/mol

First phase typical conditions, which overall contribute to yield of about 98%, are:

  • In standard atmospheres pressure is between 4–10 (410–1,000 kPa; 59–150 psi) and

  • The temperature is around 870–1,073 K (600–800 °C; 1,100–1,500 °F).

A complication that is to be considered is that it involves a side-reaction in the first step that reverts the nitric oxide back to nitrogen is shown below:

4NH3 + 6NO -> 5N2 + 6H2O

This is considered as a secondary reaction which is minimised by reducing the time the gas mixtures are in contact with the catalyst.

Looking at the Overall reaction

The first equations overall reaction is the sum of the, 3 times the second equation, and 2 times the last equation; and at the end all divided by 2:

2NH3(g) + 4O2(g) + H2O(l) -> 3H2O(g) + 2HNO3(aq)

ΔH = −740.6 kJ/mol

In the air if alternatively, if the last step is carried out, then the overall reaction is the sum of equation 1, and 2 times the equation 2, and equation 4;at the end again all divided by 2, Without considering the state of water,

NH3(g) + 2O2(g) -> H2O + HNO3(aq)

ΔH = −370.3 kJ/mol


Before getting into the different steps, we can quickly understand the principle or mechanism behind this process. The ammonias conversion to nitric acid simply occurs as a result of oxidation reaction. This oxidation reaction gives us the corresponding nitric oxide which we need. Further, when nitric acid oxidation of the is oxidized nitrous gases are formed and those gases can trap water molecule too. We obtain  As a, we obtain nitric acid. Catalytic oxidation involves O2 and is used where ammonia will give rise to the desired product.

While the process is carried out , there are particular reaction chambers where ammonia is fed from one direction and air through various different paths. Possibilities are there of side reactions occurring as well. If we go to subsequent ammonia the oxidation process will get some other reactions. Usually it happens in the case of dinitrogen. Ammonia is created by the removal of dinitrogen . If we try to oxidize the ammonia, dinitrogen will be given back, there can also be other oxidized forms as well.

In all these, optimizing the reaction condition becomes very important, otherwise, many gases can get together and form with the desired NO.Therefore It is, it is necessary to avoid side reactions.

Moving on, the next stage, it involves the oxidation of NO2 which can also dimerize to give an end result as N2O4. This reaction in the stage is only favoured at low temperatures.

Meanwhile, this process which is known as the Ostwald process is also closely related to Born Haber's Process or cycle.

FAQ (Frequently Asked Questions)

Q1. In Ostwald's Process which catalyst is used?

Ans: The process of ostwald is used to produce nitric acid. Feedstock is the ammonia for this reaction to occur. It is then reacted with water and oxygen using a platinum catalyst to produce nitric acid and this reaction is an exothermic reaction. 

Q2.  Explain Ostwald's Process in chemistry.

Ans: A chemical process is the ostwald's process which is used for making nitric acid. Wilhelm Ostwald developed this process in 1902 and patented it also. Ostwald's process is known as the ministry of the modern chemistry and chemical industry, and provides the main raw material for the most common type of fertilizer.

Q3. Why is Ostwald's Process considered as important?

Ans: The ostwald's process is considered as a very important process because it provides a key ingredient for many of the fertilizers, nitrate ions and these fertilizers improve the plants growth.

Q4. What is the Formula of Nitric Acid?

Ans: The formula of nitric acid is HNO3.