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

Na₂CO₃ + 2HCl → 2NaCl + H₂O+ CO₂ (double displacement reaction). Uses of Sodium Carbonate - In the manufacture of detergents, soaps and paper, as a wetting agent in the brick industry, an abrasive and foaming agent in toothpaste, pH modifier, and water softener. NaOH - Sodium hydroxide. NaCl - Sodium chloride.

(Calcium Oxide - CaO) - A crystalline solid, white in colour. Limestone (Calcium Carbonate - CaCO₃) - A sedimentary rock that occurs naturally.
It is a form of chalk. Slaked lime {Calcium hydroxide - Ca(OH)₂} - An ionic compound, has no colour, and it is like white powder used in plasters and whitewash. Marble - A metamorphic rock consisting of carbonate minerals that recrystallize under the influence of heat, pressure and aqueous solutions.

Chlor-Alkali Process (Electrolysis process) - It is the one in which electricity is passed through an aqueous solution of Sodium chloride or Brine, which will decompose to form Sodium hydroxide.
It is used in the manufacture of chlorine, hydrogen, and sodium hydroxide (caustic) solutions. Electrolysis Reaction - 2NaCl (Sodium Chloride) + 2H₂O (Water) → 2NaOH (Sodium Hydroxide) + Cl₂ (Chlorine) + H₂ (Hydrogen).

Part of one reactant is replaced by part of another reactant. Example - AgNO₃ (Silver Nitrate) + NaCl (Sodium Chloride) → AgCl (Silver Chloride) + NaNO₃ (Sodium Nitrate).

Oxidation reaction - A process that involves the addition of oxygen or any electronegative element or the removal of hydrogen or any electropositive element. Reaction - C + O₂ → CO₂ .
Reduction is a process that involves the addition of hydrogen or any electropositive element or the removal of oxygen or any electronegative element.
Examples: ZnO (Zinc Oxide) + C → Zn + CO. A displacement reaction occurs when another element in a compound is replaced by an element.
Example - 2NaCl (Sodium Chloride) + F₂→ 2NaF (Sodium fluoride) + Cl₂ .
A double displacement reaction is a reaction where part of one reactant is replaced by part of another reactant.
Example - 2NaCl (Sodium Chloride) + CaSO₄ (Calcium Sulphate) → Na₂SO₄ (Sodium Sulphate) + CaCl₂ (Calcium Chloride).

Neutralization reaction is when an acid and a base react to form water and salt, and involves the combination of H⁺ ions and OH⁻ ions to generate water. Examples - HCl (Hydrochloric Acid) + NaOH (Sodium Hydroxide) → NaCl (Sodium Chloride) + H₂O (Water).

Decomposition Reaction - A chemical reaction in which one reactant breaks down into two or more products. Example - CaCO₃ → CaO + CO₂ . Combination Reactions - The reactions in which two or more substances combine to form a single substance. Example - 2Mg + 𝑂₂ → 2MgO and H₂ + Cl₂  → 2HCl.

In a chemical equation the subscript (s) = solid state, + = used to separate multiple reactants or products, → = yield sign; separates reactants from products, ⇋ = replaces the yield sign for reversible reactions that reach equilibrium, ∆ = triangle indicates that the reaction is being heated, (l) = reactant or product in the liquid state and (g) = Gas.

Reduction is the loss of oxygen. Oxidation is the gain of oxygen. A reduction-oxidation (redox reaction) is a chemical reaction in which reduction and oxidation occur at the same time.
Dehydrogenation is a chemical reaction by which hydrogen is removed from an organic compound to form a new chemical.
It is the reverse of hydrogenation. Combination reaction is a type of reaction in which two or more elements or compounds combine to form a single compound.

BaBr₂ (Barium Bromide) is metallic alkaline in nature. Uses - Fractional crystallisation to purify radium and as a precursor in chemicals, photography, and manufacturing of other bromides.
2KBr (Potassium Bromide) + BaI₂ (Barium iodide) → 2KI (Potassium iodide) + BaBr₂ (Barium Bromide). This is a Double Displacement Reaction because the bromide and iodide ions are shifted.
Double Displacement Reaction - A type of reaction where part of one reactant is replaced by part of another reactant. It is represented as AB + CD → AC + BD.