Ammonia 

Ammonia (NH₃) is a colourless gas with a sharp, pungent odour. It comprises nitrogen and hydrogen and is vital for various industrial applications and biological processes.

1.0Introduction     

Ammonia, with the chemical formula NH₃, is a nitrogen- and hydrogen-based compound consisting of one nitrogen and three hydrogen atoms.

Ammonia is produced by decomposing nitrogenous organic matter, such as urea (NH₂CONH₂).

           NH₂CONH₂ + 2H₂O → (NH₄)₂CO₃  ⇌ 2NH₃ + CO₂ + H₂O

The natural breakdown of animal and plant matter releases ammonia because the nitrogen compounds present decompose as the organisms die or decay. Additionally, ammonia can be found in soil as ammonium salts.

2.0Structure Of Ammonia 

The ammonia molecule is formed when three sp³ hybrid orbitals of nitrogen overlap with three s hydrogen orbitals. A lone pair of electrons occupies the fourth sp³ hybrid orbital of nitrogen, giving the ammonia molecule its trigonal pyramidal structure.

The H-N-H bond angle in ammonia is 107.8°, and the N-H bond length is 101.7 pm. The bond angle is smaller than the tetrahedral angle of 109°28' due to lone pair-bond pair repulsion, which pushes the N-H bonds somewhat inward. In its liquid and solid forms, ammonia is linked through hydrogen bonding.

3.0Physical Properties of Ammonia

4.0Chemical  Properties of Ammonia

Nessler's Reagent Reaction:

• Ammonia gives a reddish-brown precipitate with Nessler's reagent (potassium tetraiodomercurate(II), K₂HgI₄).
• This reaction is used as a qualitative test for the presence of ammonia.

Combustibility:

• Ammonia neither burns nor supports combustion.

Basic Nature:

• Dry ammonia is neutral.
• Aqueous ammonia (ammonium hydroxide, NH₄OH) acts as a weak base.

Reactions

1. With Acids:

• Ammonia reacts with acids to form ammonium salts: 

NH₃(g) + HCl(g) → NH₄Cl(s)

2NH₃(g) + H₂SO₄ → (NH₄)₂SO₄

2. With Metallic Salts:

• Ammonia dissolved in water forms ammonium hydroxide:   

NH₃+ H₂O → NH₄OH

• Ammonium hydroxide reacts with metallic salts to form insoluble precipitates: 

NH₄OH + FeCl₃ → 3NH₄Cl + Fe(OH)₃

NH₄OH + CuSO₄  → (NH₄)2SO₄ + Cu(OH)₂

3. Formation of Urea:

• Ammonia reacts with carbon dioxide to form urea at 423 K and 150 atmospheric pressure

2NH₃ + CO₂ → NH₂CONH₂ + H₂O

4. Dissociation of Ammonia:

• Ammonia can dissociate into nitrogen and hydrogen when passed through a red-hot tube or electric spark:

 2NH₃  ⇌  N₂ + 3H₂

5. Oxidation of Ammonia:

• Ammonia reacts with oxygen when heated in the presence of platinum at 800°C to yield nitric oxide: 

4NH₃ + 5O₂→ 4NO + 6H₂O + heat energy

• Nitric oxide then reacts with oxygen to form nitrogen dioxide: 

2NO + O₂ → 2NO₂

6. Reaction with Metal Oxides:

• Ammonia reduces metal oxides to free metals:

 2NH₃ + 3CuO → 3Cu + 3H₂O + N_2​

7. Reduction of Halogens:

• Ammonia reduces halogens to hydrogen halides: 

2NH₃ + 3Cl₂ → N₂+ 6HCl

5.0Formation and Production of Ammonia

Ammonia (NH₃) is found in small quantities in the air and soil, primarily formed by the decay of nitrogenous organic matter such as urea. The decomposition reaction is as follows:

• NH₂CONH₂ + 2H₂O → (NH₄)2CO₃  → 2NH₃ + CO₂ + H₂O

Small Scale Production

Ammonia can be obtained from ammonium salts by treating them with caustic soda (NaOH) or calcium hydroxide (Ca(OH)₂). The reactions are:

• 2NH₄Cl  + Ca(OH)₂  → 2NH₃  + 2H₂O + CaCl₂
• (NH₄)₂SO₄ + 2NaOH →  2NH₃  + 2H₂O +  Na₂SO₄

Large Scale Production: Haber’s Process

Ammonia is manufactured using the Haber’s process on a large scale. The chemical reaction for ammonia synthesis is:

•  N₂(g) + 3H₂(g) ⇌ 2NH₃(g);       (ΔH ⁰ = −46.1 kJ mol⁻¹)

According to Le Chatelier's principle, high pressure favours the formation of ammonia. The optimal conditions for ammonia production include:

• Pressure: 200 × 10⁵ Pa (approximately 200 atm)
• Temperature: ~ 700 K
• Catalyst: Iron oxide with small amounts of K₂O and Al₂O₃ contributes to increasing the equilibrium attainment rate.

Iron was used as a catalyst, and molybdenum was used as a promoter.

6.0Preparation of Ammonia

Ammonia can be prepared using the following methods:

• From Ammonium Chloride Ammonia gas is commonly produced in laboratories by heating ammonium chloride (NH₄Cl) with slaked lime (Ca(OH)₂).

           2NH₄Cl + Ca(OH)₂  + Heat → 2NH₃ + 2H₂O + CaCl₂

• Hydrolysis of Metal Nitrides Ammonia gas can also be produced by hydrolysing metal nitrides such as magnesium nitride and aluminium nitride with water or alkalis.

           Mg₃N₂  +  6H₂O  →  2NH₃  + 3Mg(OH)₂

           AlN  +  3H₂O  →  NH₃  + Al(OH)₃

7.0Uses of Ammonia

Ammonia has a variety of uses across different industries due to its chemical properties. Here are some of the key uses of ammonia:

• Refrigerant: Ammonia in its aqueous state (ammonium hydroxide) is used as a refrigerant, particularly in industrial refrigeration systems. Its excellent thermodynamic properties make it efficient for heat absorption and transfer.
• Manufacturing of Urea: Ammonia produces urea (NH₂CONH₂), a widely used nitrogenous fertilizer. Urea provides essential nitrogen to plants, enhancing their growth and productivity.
• Cleaning Agent: Ammonia, also known as azane, possesses strong cleansing properties. It effectively removes grease and stains, making it a common ingredient in household and industrial cleaning products.