Railway Science (Chemistry-Chemical Reaction)

Neutralization reaction - An acid-base reaction in which an acid reacts with a base to form salt and water. Example - 2LiOH + H₂SO₄ → Li₂SO₄ (Lithium Sulphate) + 2H₂O (water). The pH of the neutralized solution depends upon the acid strength of the reactants and their concentrations.
There are 4 types of neutralization reactions, depending on whether the acid and base are strong or weak: Strong Acids and Strong Bases, Strong Acids and Weak Bases, Weak Acids and Strong Bases, Weak Acids and Weak Bases.

Neutralization reaction - A chemical reaction in which an acid and base react together to form salt and water as products. It is a combination of H⁺ ions and OH⁻ ions which form water.
Example - Acid + Base → Water + Salt. Chemical names - NaOH (Sodium hydroxide), HCl (Hydrochloric acid), HNO₃ (Nitric acid), NaCl (Sodium chloride), KNO₃ (Potassium nitrate).

CuSO₄ (Copper Sulphate) + Ca (Calcium) → CaSO₄ (Calcium Sulphate) + Cu(Copper). Examples of some chemical reactions:- Combination Reaction (3 H₂ + N₂→ 2 NH₃), Decomposition Reactions (H₂CO₃ → H₂O + CO₂), Combustion Reactions (C₂H₄ + 3 O2→ 2 CO2 + 2 H₂O), Acid Base Neutralization Reactions (HCl + NaOH → H₂O + NaCl), Double Replacement Reactions (Na₂CO₃ + BaBr₂ → 2 NaBr + BaCO₃), Redox Reactions (Zn + CuCl₂ → Cu + ZnCl₂).

An oxidation-reduction reaction (redox reaction) is a chemical process in which electrons are transferred between two reactants that are involved. Oxidation reaction is a process in which oxygen is gained, or hydrogen is lost. Reduction reaction is one in which hydrogen is gained, or oxygen is lost. The addition of an oxygen atom to ethanol produces ethanoic acid. Since the hydrogen atom is removed and oxygen is added it is an oxidation process.

Photo decomposition Reaction is a chemical reaction in which a compound gets broken down into simple substances under its exposure to light. When silver chloride crystals which are white in colour are kept under sunlight, they turn into gray color as it loses chlorine gas.
A single compound, i.e AgCl is breaking down when exposed to light and producing different compounds - Silver(Ag) and Chlorine(Cl). Therefore, this reaction is a photo decomposition reaction.

A chemical reaction is in which the bonds are broken within reactant molecules, and new bonds are formed within product molecules in order to form a new substance.
Eg; metabolism of food in our body, a burning candle etc. A chemical equation is a mathematical statement which symbolizes the product formation from reactants while stating certain conditions.
In order to assure the law of conservation of mass, a chemical equation must be balanced i.e. the number of atoms on both sides must be equal called the balancing of the equation.

Oxidation - Gain of Oxygen or loss of Hydrogen (loss of electrons). Reduction - Gain of Hydrogen or loss of Oxygen (gain of electrons).
Oxidizing agents - Add oxygen to another substance or remove hydrogen from it (take electrons). Reducing agents - Remove oxygen from another substance or add hydrogen to it (give electrons).

The chemical reaction will be NaOH (aq) + HCl (aq)→NaCl (aq) + H₂O (l). It is an example of a double displacement reaction. Neutralization reaction - chemical reaction in which an acid and base quantitatively react together to form a salt and water as products.

Electrolytic Decomposition Reaction - Decomposition of any molecule by using electricity. Example, Electrolysis of water - 2H₂O→2H₂ + O₂ and 2NaCl  →2Na + Cl₂ .
Thermal decomposition reaction - when heat is applied on any chemical compound or molecule, it breaks down (decomposes) into two or more (multiple) chemical substances.
Example - ZnCO₃→ ZnO + CO₂ and 2KCIO₃→2KCl + 3O₂ . Photolytic decomposition reaction - which requires the presence of light. Example - 2AgBr → 2Ag + Br₂ .

Combination reaction - Two or more compounds combine to form one compound. A + B → AB. Decomposition reaction - a complex molecule breaks down to make simpler ones.AB → A + B.
Examples - ZnCO₃ → ZnO + CO₂ & 2NaCl → 2Na + Cl₂ . Displacement reaction - One element gets displaced with another element in the compound. A + BC → AC + B. Example - MgCl₂ + Na→ 2NaCl + Mg.