Matter, Atoms and Molecules RRB PYQ

The reaction CaCO3 → CaO + CO2 is a classic example of a thermal decomposition reaction.

A decomposition reaction involves a single compound breaking down into two or more simpler products. This type of reaction is generally endothermic, requiring energy in the form of heat, light, or electricity. For example, water (H2O) decomposes into hydrogen (H2) and oxygen (O2) when electricity is applied. Decomposition reactions are vital in industrial processes and the natural breakdown of organic materials.

In the reaction Ca(OH)2 + A → CaCl2 + H2O, hydrochloric acid (HCl) acts as reactant A, reacting with calcium hydroxide to produce calcium chloride and water, exemplifying a neutralisation reaction. The balanced equation is: Ca(OH)2 + 2HCl → CaCl2 + 2H2O. Neutralisation involves an acid and a base reacting to yield water and a salt, with no excess hydrogen or hydroxide ions present.

In a chemical equation, the reaction conditions, like temperature, pressure, or catalysts, are typically indicated above or below the arrow. Above the arrow is most common for conditions such as temperature or catalysts, while below may show additional specific conditions. This placement helps chemists understand and replicate the conditions necessary for the reaction to proceed effectively and obtain consistent results.

Chlorine gas reacts with potassium iodide solution in a displacement reaction, where chlorine displaces iodine from the solution to form potassium chloride and iodine. In displacement reactions, one element replaces another in a compound based on reactivity.

In a gas or liquid, particles have enough kinetic energy to completely overcome intermolecular forces. This results in particles being far apart with large empty spaces between them, moving randomly and quickly in all directions, which explains how ink spreads evenly in water without stirring.

Rancidity occurs due to the oxidation of fats and oils, which leads to unpleasant smells and flavors. This process can be accelerated by factors like water, exposure to metal atoms, and microbial activity. Corrosion refers to the deterioration of metals through chemical reactions with their environment.

Covalent compounds typically dissolve in organic solvents but not in water. They are formed by sharing electrons, do not generally form ions, and are poor conductors of heat and electricity due to the absence of free electrons or ions.

During the electrolysis of water, hydrogen and oxygen gases are released in the ratio 2:1 by volume. Water contains two hydrogen atoms and one oxygen atom, as shown by its formula H2O. The process breaks water into hydrogen at the cathode and oxygen at the anode. The balanced reaction is 2H2O → 2H2 + O2, which clearly shows the 2:1 gas ratio.

Carbon cannot form a C4+ ion because removing four electrons requires a tremendous amount of energy. Due to carbon's small size and high ionization energy, it tends to share electrons rather than lose or gain them. This makes forming a C4+ ion highly unfavorable and impractical under normal conditions.