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

Combination reaction - A reaction in which two reactants combine to form one product. Example of combination reaction - NH₃ (Ammonia) + HCl (Hydrochloric Acid)→ NH₄Cl (Ammonium Chloride), 2H₂ + O₂ → 2H₂O (Water), C + O₂ CO₂ → (Carbon Dioxide).

A reaction which has an equal number of atoms of all the elements on both sides of the chemical equation is called a balanced chemical equation.
Example - 3Fe (s) + 4H₂O (l) → Fe₃O₄ (s) + 4H₂ (g).

Double displacement reaction: A reaction in which two reactants exchange ions to form two new compounds. Decomposition reaction: A chemical reaction in which one reactant breaks down into two or more products. Example: 2HgO(s)→2Hg(l)+O₂(g).
Combination reaction: A reaction in which two or more substances combine to form a single new substance. Example: 2Na(s) + Cl₂(g) → 2NaCl(s). Single Displacement reaction: A reaction that replaces part of one reactor with another. Example : Fe + CuSO₄ (aq)→FeSO₄(aq) + Cu (s).

Exothermic reaction is a reaction that releases energy into the environment in the form of heat. Examples include any combustion process, rusting of iron, and freezing of water. Endothermic reactions are chemical reactions in which the reactants absorb heat energy from the surroundings to form products. Examples: melting ice cubes and melting solid salts.

The chemical equation is:- (Pb(NO₃)₂(aq) + 2 KI(aq)→ PbI₂(s)+ 2KNO₃(aq). When aqueous lead nitrate is added to potassium iodide, Iodide ion displaces nitrate from lead nitrate and Nitrate displaces iodine from potassium iodide. Thus, two new products, Potassium nitrate and lead iodide are formed. Lead(II) nitrate (Pb(NO₃)₂) is an inorganic compound.

A reaction in which energy is released in the form of light or heat. CaO(quick lime) + H₂O ⟶ Ca(OH)₂ (slaked lime) + heat. A dissociation reaction when larger molecules will dissociate to form new molecules by the use of some energy.
A double displacement reaction in which the reactant ions exchange places to form new products. A displacement reaction that replaces part of one reactor with another.

Discovered by - Henry Cavendish (1766). Isotopes of Hydrogen - Protium ( ¹H), Deuterium ( ²H), and Tritium ( ³H). Uses - Energy production, Chemical production, Food production, Semiconductor production, Welding and metalworking, Medical applications, Balloons.
Chemical reaction - Process in which one or more reactants are converted to one or more different products. Displacement reaction - Reaction that replaces part of one reactant with another. Eg - Zn (Zinc) + 2HCl (Hydrochloric Acid) → ZnCl₂ (Zinc Chloride) + H₂ (Hydrogen).

A neutralization reaction is a combination of H⁺ ions and OH⁻ ions which form water. Acid + Base → Salt + Water. HCl (hydrochloric acid) + NaOH (sodium hydroxide) → NaCl (Sodium Chloride /Common Salt /table salt) + H₂O (Water). Strength of Acid and Base is measured on pH scale (1-14) - below 7 (acidic nature) and above 7 (basic nature).

CaO (Calcium oxide) + H₂O (Water) → Ca(OH)₂ (Calcium hydroxide / Slaked lime) : Combination reaction. It liberates heat therefore, this is an exothermic reaction. A neutralization reaction is a combination of H⁺ ions and OH⁻ ions which form water. Reaction - Acid + Base → Salt + Water. Nitric Acid (HNO₃). Potassium hydroxide (KOH). Phosphoric acid (H₃PO₄). Tripotassium phosphate (K₃PO₄).

SO₂ (Sulphur dioxide) + 2H₂S (Hydrogen Sulphide) → 3S (Sulphur) + 2H₂O (water). It is an example of redox reaction (combination of oxidation and reduction reaction).