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

Redox reaction:- It is a chemical reaction in which reactants lose and gain electrons. The chemical equation for the reaction is: CuO + H₂ → Cu + H₂O. In this reaction, copper oxide (CuO) is reduced to copper (Cu) while hydrogen (H₂) is oxidized to water (H₂O).
The reduction of copper oxide involves the gain of electrons by copper ions, while the oxidation of hydrogen involves the loss of electrons by hydrogen atoms.

Double displacement. Example - AgNO₃ (Silver nitrate) + NaCl (sodium chloride) → AgCl (silver chloride) + NaNO₃ (sodium nitrate).
Displacement reaction - Chemical reaction in which a more reactive element displaces a less reactive element from its compound. Example - Zn (Zinc) + FeSO4 (ferrous sulfate) → ZnSO4(Zinc sulfate) + Fe (Iron).

The Reaction is: NaOH (sodium hydroxide) + HCl (hydrochloric acid) → NaCl (sodium chloride) + H₂O (Water). It is a type of neutralization reaction. neutralization reaction - an acid and a base that results in an ionic compound and possibly water. it is represented by (acid + base → water + salt).

Copper carbonate - A green blend that is formed when the copper reacts with carbon dioxide. Blue-green algae - A type of bacteria that can grow on copper utensils, but they are not responsible for the green coating.
Lichen - A type of plant that can grow on copper utensils, but it is not responsible for the green coating. Magnesium carbonate - A white compound that is not formed when the copper reacts with humid air.

Galvanic Cell - An electrochemical cell that converts the chemical energy of spontaneous redox reactions into electrical energy. Clark cell - A wet-chemical cell that produces a highly stable voltage.
Electrolytic cell - Any device in which electrical energy is converted to chemical energy, or vice versa. Electrochemical cells - A power generating device that turns chemical energy into electrical energy. Types of Cells - Primary Cell, Secondary cell, Reserve cell, Fuel cell.

Endothermic Reaction: Chemical reactions in which the reactants absorb heat energy from the surroundings to form products.

Carbon dioxide (CO₂) reacts with limewater (a solution of calcium hydroxide, Ca(OH)₂), to form a white precipitate (appears milky) of calcium carbonate, CaCO₃ .

Metals react with water and produce a metal oxide and hydrogen gas. Metal oxides that are soluble in water dissolve in it to further form metal hydroxide. Metals like aluminum, iron and zinc do not react either with cold or hot water. But they react with steam to form the metal oxide and hydrogen. Metals such as lead, copper, silver and gold do not react with water at all.

Corrosion refers to the process by which metals are gradually destroyed or deteriorated due to chemical or electrochemical reactions with their surrounding environment. Galvanisation is a method of protecting steel and iron from rusting by coating them with a thin layer of zinc.

The balanced chemical equation for the combustion of iron (Fe) in the presence of oxygen (O₂) to form iron oxide (Fe₂O₃) is : 4Fe + 3O2 → 2Fe₂O₃