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

2 Mg (Magnesium) + O₂ (Oxygen) → 2MgO (Magnesium oxide). When a reactant loses electrons during a reaction, it is called Oxidation. It is the gain or addition of oxygen.
Example - C + O₂ → CO₂ (oxidation of carbon). When a reactant accumulates electrons during a reaction, it is called Reduction. It is the loss of oxygen. Example - Addition of hydrogen. N₂ + 3H₂ → 2NH₃ (reduction of nitrogen).

HCl (Hydrogen chloride) + CuO (Copper oxide) → CuCl₂ (Copper (II) chloride) + H₂O (water). This is a double displacement reaction ( in which two reactants exchange ions to form two new compounds).
Example - Silver nitrate reacts with sodium chloride to form silver chloride and sodium nitrate.

Carbon dioxide (CO₂) + Lime water [Ca(OH)₂ ] → Calcium Carbonate(CaCO₃) + Water (H₂O). In this reaction turning lime water into milky is a standard test of carbon dioxide. Reactions in which heat is released along with the formation of products are called exothermic chemical reactions. Examples - Burning of natural gas CH₄ (Methane) + 2O₂ (Oxygen) → CO₂ (Carbon dioxide) + 2H₂O (Water).

Zn (zinc) + 2AgNO₃ (silver nitrate) → Zn  (N𝑂₃)₂  (zinc nitrate) + 2Ag (silver). Balanced chemical equation - A chemical equation in which the number of each type of atom is equal on both sides of the equation.
A single displacement reaction is a reaction in which a single element is replaced by another element that is part of a compound.

Combination reaction is a reaction in which two or more substances combine to form a single new substance. Example - CO(Carbon monoxide) +2𝐻₂ (Hydrogen) → C𝐻₃OH(Methanol). 2Mg(Magnesium)  + 𝑂₂ (Oxygen) → 2MgO(Magnesium 2 Oxide)

2PbO (Lead oxide) + C (Carbon) → 2Pb (Lead) + 1CO₂ (Carbon Dioxide). Lead (Pb) - Atomic number (82), Atomic mass (207.2). Properties - low melting point, ease of casting, high density, low strength, ease of fabrication, acid resistance.
Uses - batteries, gas sensors, pigments, ceramics, and glass industry. Carbon: Atomic number (6), Atomic mass (12). Properties - Boiling Point(4827°C), isotopes (carbon-12, carbon-13 and carbon-14).

Exothermic reaction - Energy is released during the process of respiration. Example - Snow Formation in Clouds, Burning of a Candle, Rusting of Iron, Burning of Sugar.
Examples of Endothermic reaction - photosynthesis, evaporating liquids, melting ice, dry ice, alkane cracking, thermal decomposition, ammonium chloride in water.
Example of Redox reaction - PbO (Lead oxide) + H₂ (Hydrogen) → Pb (Lead) + H₂O (Water). Example of Displacement reaction - Mg (Magnesium) + 2HCl (Hydrochloric Acid) → MgCl₂ (Magnesium Chloride) + H₂ (Hydrogen). Zn (Zinc) + H₂SO₄ (Sulphuric Acid) → ZnSO₄ (Zinc Sulphate) + H₂ (Hydrogen).

Combination Reaction - A reaction in which two or more reactants combine to form a single product. X + Y → XY. Calcium hydroxide (slaked lime) is formed by mixing water and calcium oxide (CaO). CaO + H₂O → Ca(OH)₂ .

A reaction in which one element is replaced by another element of the compound is known as displacement reaction. Examples- 2NaCl (Sodium Chloride) + F₂ (Fluorine) → 2NaF (Sodium fluoride) + Cl₂ (Chlorine), 2HCl (Hydrochloric acid) + Zn (Zinc) → ZnCl₂ (Zinc Chloride) + H₂ (Hydrogen).

Barium sulfate (BaSO₄) - It is a white crystalline solid that is odorless and insoluble in water. It is used to help diagnose or find problems in the esophagus, stomach and bowels.
It is a radiographic contrast agent. Potassium Sulfate (K2SO₄) occurs naturally in volcanic lava and salt lakes. It appears as a colourless to white crystalline powder or crystals.
Potassium Chloride (KCl) is a mineral (electrolyte) and it provides potassium for the body. Barium chloride (BaCl₂) is an odorless white crystalline solid that is used in the manufacture of various barium salts.