Correct Option
The correct option is 1 and 2 only
Explanation
Chemical reactions are classified based on energy changes. Exothermic reactions are those in which heat is evolved or released along with the formation of products. Conversely, endothermic reactions require energy (in the form of heat, light, or electricity) to break down reactants.
Statement-wise Analysis
- Statement 1 is Correct: The reaction of quick lime (Calcium oxide, CaO) with water to form slaked lime (Calcium hydroxide, Ca(OH)2) is a combination reaction. This process releases a large amount of heat, making it highly exothermic.
- Statement 2 is Correct: The decomposition of vegetable matter into compost is carried out by microbes. This biological breakdown releases energy in the form of heat, classifying it as an exothermic reaction.
- Statement 3 is Incorrect: The thermal decomposition of calcium carbonate (CaCO3) into calcium oxide and carbon dioxide requires the supply of heat energy. Since energy is absorbed to break the bonds, it is an endothermic reaction.
- Statement 4 is Incorrect: The decomposition of silver chloride (AgCl) into silver and chlorine occurs in the presence of sunlight. The reaction absorbs light energy to proceed, making it an endothermic process (specifically, a photochemical decomposition).
Key Takeaway: Generally, decomposition reactions are endothermic as they require energy to break bonds, whereas combination reactions and respiration/decomposition of organic matter are exothermic as they release energy.