Railway Science (Chemistry-Chemical Reaction) (Part-VII)

Thermal decomposition - It is a chemical process of breaking down Compounds due to high temperatures. Heat is required to break chemical bonds in the substance being decomposed.
This reaction is frequently endothermic. Reaction - NH₄NO₃ (Ammonium Nitrate) → N₂O (Nitrous Oxide) + 2H₂O (Water) and CuCO₃ (Copper Carbonate) → CuO (Copper Oxide) + CO₂ (Carbon Dioxide).

When CO₂ reacts with lime water {Ca(OH)₂} it turns into Calcium Carbonate (CaCO₃) which is of milky color. CO₂ (Carbon Dioxide)+ Ca (OH)₂ (Lime Water) → CaCO₃ (Calcium Carbonate) + H₂O (Water). Sulphur dioxide can also turn Milky when reacting with lime water. SO₂ (Sulphur dioxide) + Ca(OH)₂ (Lime Water) → CaSO₃ (Calcium sulfite) + H₂O (Water).

SnCl₂ (Stannous chloride) + 2HgCl₂ (Mercury (II) Chloride) → Hg₂Cl₂ (Mercury (I) Chloride ) + SnCl₄ (Stannic Chloride). In the given reaction oxidation of stannous chloride to stannic chloride is occurring because of the addition of electronegative element chlorine to it. This increases the oxidation state of Sn from +2 to +4.

Lead nitrate on heating decomposes to lead monoxide, nitrogen dioxide and oxygen. 2Pb(NO₃)₂ (Lead nitrate) → 2PbO (lead oxide) + 4NO₂ (Nitrogen dioxide) + O₂(Oxygen).
NO₂ (Nitrogen dioxide) is released, along with oxygen, as a reddish-brown gas. Compound - Nitrogen dioxide - NO₂ , Nitrogen pentoxide - N₂O₅ , Nitric Oxide - NO.

Carbon Dioxide (CO₂) appears as a colorless, odorless gas at atmospheric temperatures and pressures. Relatively nontoxic and noncombustible. It is used as a refrigerant, in fire extinguishers, promoting the growth of plants in greenhouses, When Baking Soda (Sodium Bicarbonate (2NaHCO₃) is heated, it progressively decomposes to generate sodium carbonate (Na₂CO₃), water (H₂O), and carbon dioxide (CO₂) gas. The reaction is decomposition reaction : 2NaHCO₃ → Na₂CO₃ + H₂O + CO₂ .

Redox reaction - The reactions in which oxidation and reduction take place simultaneously. Oxidation Reaction - A reaction in which either the addition of Oxygen takes place or the removal of Hydrogen takes place.
Reduction Reaction - A reaction in which either the addition of Hydrogen takes place or the removal of oxygen takes place. The species that loses electrons is said to be oxidized, while the species that gains electrons is said to be reduced.

It is formed due to the precipitation of the insoluble suspension of Calcium carbonate: The precipitate of Calcium carbonate will settle down at the bottom. Ca(OH)₂ (Calcium hydroxide) + CO₂ (Carbon Dioxide) → CaCO₃↓ (Calcium carbonate) + H₂O (water).
Properties - It is a calcium salt, a carbonate salt, a one-carbon compound and an inorganic calcium salt. Uses - It has a role as an antacid, a food coloring, a food firming agent and a fertilizer.

Reaction - Na₂CO₃ + 2HCl → 2NaCl + H₂O + CO₂ The acid (HCl) reacts with the base (Na₂CO₃) to form a salt (NaCl), water (H₂O) and carbon dioxide gas (CO₂). The reaction releases carbon dioxide gas which appears as bubbles and causes brisk effervescence.

Electrolytic decomposition of solution gives Cl₂ (g) at the anode (positive electrode) and 𝐻₂ (g) and NaOH (aq) are formed at cathode (negative electrode). The whole process is known as the chlor-alkali electrolysis process.

Reaction - Zn (Zinc) + FeCl₂ (Iron Chloride) → ZnCl₂ (Zinc Chloride) + Fe (Iron). Displacement reactions can be used to find out the relative reactivities of metals.
A more reactive metal displaces a less reactive metal from its salt solution. Example: Zn (Zinc) + CuSO₄ (Copper Sulphate) → ZnSO₄ (Zinc Sulphate) + Cu (Copper).