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

Sodium(Na) and Potassium (K) are metals located in the s-block of the periodic table and are highly reactive. That's why it is kept immersed in kerosene to avoid contact with air. They remain inactive in kerosene.

When silver comes into contact with sulphur, a chemical reaction occurs, resulting in the formation of silver sulphide (Ag₂S). It is a black compound that causes the silver to appear tarnished or blackened.
This reaction is commonly observed when silver jewellery or silverware is exposed to sulphur-containing compounds, such as hydrogen sulfide (H₂S) gas in the air.

The presence of any of the following changes helps us to determine that a chemical reaction has taken place: Formation of new substance(s), Change in state, Change in colour, Change in temperature, Formation of a precipitate, Evolution of a gas.

When magnesium reacts with oxygen in the air during combustion, it forms magnesium oxide (white, powdery substance). The chemical equation for this reaction - 2Mg + O₂ → 2MgO. Magnesium (Mg) Atomic number - 12 discovered by Joseph Black in 1755.

Sublimation is the process in which a solid directly converts into a gas without going through the liquid phase. Example - Camphor, naphthalene, ammonium chloride, iodine, and dry ice. Nitrogen - {(N), atomic number - 7}. Sucrose - C₁₂H₂₂O₁₁. Calcium - {(Ca), atomic number - 20}.

Thermal decomposition reaction: A reaction in which a compound breaks down into simpler substances upon heating. Electrolytic decomposition reaction: A reaction in which a compound is broken down into its constituent elements using an electric current.
Photo decomposition reaction: A reaction in which a substance is broken down into simple substances by exposure to light (photons). Exothermic reaction: a chemical reaction that releases energy in the form of light or heat.

Law of Constant Proportion (Joseph Proust) - A chemical compound always contains exactly the same proportion of elements by mass. Law of Reciprocal Proportion (Ritcher) - When two elements combine separately with the same mass of the third element then the ratio of their masses in which they do so are either the same or a simple multiple of the mass ratio in which they combine with each other. Law of Conservation of Energy - Energy can neither be created nor be destroyed but can be transformed from one form to another.

Exothermic reactions (combustion reaction) : CH₄(g) + 2O₂ (g) → CO₂ (g) + 2H₂O (g) + Heat.

Ethanol: It is liquid at room temperature because molecules are strongly associated with each other due to the presence of hydrogen bonding. It is commonly called alcohol and is the active ingredient of all alcoholic drinks.
In addition, because it is a good solvent, it is also used in medicines such as tincture iodine, cough syrups, and many tonics. It is also soluble in water in all proportions.

Single displacement reaction - Chemical reactions in which one element replaces another element from its salt or compound. Example : Fe (Iron) + CuSO₄ (Copper sulphate) → FeSO₄ (Ferrous sulphate) + Cu (Copper).
Double displacement reaction - A part of two ionic compounds is exchanged and makes two new components. Example : NaOH + NH₄Cl → NaCl + NH₄OH. Combination reaction - Two or more substances combine to form a single new substance. Example : H₂ +Cl₂→ 2HCl.
Decomposition reaction - One reactant breaks down into two or more products. Example : H₂CO₃→ H₂O + CO₂ .