Preparation of Ammonia

• Using a strong base to heat ammonium salts: Ammonia is made on a small scale by heating ammonium salts with a strong base.

(NH₄)₂SO₄ + 2NaOH + Heat→2NH₃ + 2H₂O + Na₂SO₄  

NH₄Cl+KOH+Heat→NH₃+H₂O+KCl

• Ammonia is made in the lab by heating a mixture of slaked lime and ammonium chloride.

2NH₄Cl+Ca(OH)₂+Heat→2NH₃+2H₂O+CaCl₂

• The hydrolysis of metal nitrides, such as magnesium and aluminium nitride, with water or alkalis, can also yield ammonia gas.

Mg₃ N₂+6H₂O→2NH₃+3Mg(OH)₂

AlN+3H₂O→NH₃+Al(OH)₃

By passing ammonia gas over quicklime, it is dried (CaO). Because ammonia is a basic gas, it cannot be dried by passing it through concentrated sulphuric acid or phosphorus pentoxide, as it will react with them to generate ammonium sulphate or ammonium phosphate. Calcium chloride cannot be used to dry ammonia gas because calcium chloride creates ammoniates.

Preparation of Ammonia by Haber Process

On a commercial scale, ammonia is manufactured by Haber’s process.

N₂(g) + 3H₂(g) ⇌ 2NH₃(g) ; ΔH^∘=–92.4kJ/mol

This is a reversible, exothermic reaction that occurs when the volume decreases. As a result, according to Le Chatelier’s principle, the best conditions for producing ammonia are:

1. Low temperature: Because the forward process is exothermic, the generation of ammonia is favoured at low temperatures. The rate of reaction, however, will be slow at low temperatures. The reaction’s optimal temperature has been determined to be around 700K.
2. High pressure will favour the creation of ammonia since the forward reaction happens with a decrease in volume. At a pressure of 200×10⁵Pa (200 atmospheres), the reaction is normally carried out.
3. Catalyst: The reaction rate is relatively slow, at roughly 700K. Iron oxide is used as a catalyst, along with a minor amount of K₂O and Al₂O₃. The addition of molybdenum as a promoter improves the efficiency of the catalyst.

Haber’s technique compresses a mixture of N₂ and H₂ in a 1:3 molar ratio to roughly 200-atmosphere pressure. After cooling, the compressed gases are transported through a soda-lime tower to remove moisture and carbon dioxide. These are then fed into a catalyst chamber containing iron oxide, a small amount of k₂O, and Al₂O₃. When the two gases combine to make ammonia, the chamber is heated electrically to a temperature of 700K. Because the process is exothermic, the heat generated keeps the temperature at the desired level, and no additional electrical heating is necessary.

The gases seeping from the chamber contain around 15–20 % ammonia, with the rest being nitrogen and hydrogen with no reaction. They pass via the condensing pipe, which liquefies the ammonia in the receptor and collects it. The unreacted gases are pumped back to the compression pump, where they are mixed with a new gas combination.

Ammonia (NH₃) is a colorless gas with a sharp, pungent odor. It is a compound of nitrogen and hydrogen and plays a crucial role in both the industrial sector and biological processes.

Let’s learn about ammonia in detail, including its structure, properties and uses.