State whether the following reactions are endothermic or exothermic :(a) \(\mathrm{NaOH + HCl \rightarrow NaCl + H_2O + Heat}\)(b) \(\mathrm{2KClO_3(s) \xrightarrow{\Delta} 2KCl(s) + 3O_2\uparrow}\)(c) \(\mathrm{CaO + H_2O \rightarrow Ca(OH)_2 + Heat…

Answer: (a) Exothermic; (b) endothermic; (c) exothermic.

(a) \(\mathrm{NaOH + HCl \rightarrow NaCl + H_2O + Heat}\): heat is written on the product side, i.e. heat is given out during neutralisation, so the reaction is exothermic.

(b) \(\mathrm{2KClO_3(s) \xrightarrow{\Delta} 2KCl(s) + 3O_2\uparrow}\): potassium chlorate decomposes only when heat is supplied continuously (shown by Δ over the arrow). As per the textbook, a reaction in which heat has to be supplied is classified as endothermic. (Note: strictly, in thermochemistry the overall decomposition of KClO₃ releases a little heat and the heating only supplies the activation energy; however, the SSC textbook exercise lists it as endothermic, and that is the answer expected in the board examination.)

(c) \(\mathrm{CaO + H_2O \rightarrow Ca(OH)_2 + Heat}\): quicklime reacts with water giving out a large amount of heat, so the reaction is exothermic.