alleryIdentify the reaction that is exothermic:
ACaO + H$_2$O $\longrightarrow$ Ca(OH)$_2$ + heat
B2KClO$_3$(s) $\longrightarrow$ 2KCl(s) + 3O$_2\uparrow$
CCaCO$_3$(s) $\longrightarrow$ CaO(s) + CO$_2\uparrow$
DCaCO$_3$ + heat $\longrightarrow$ CaO + CO$_2$
Answer & Solution
Correct answer: A. CaO + H$_2$O $\longrightarrow$ Ca(OH)$_2$ + heat
1. An exothermic reaction shows heat released on the product side.
2. In CaO + H$_2$O $\longrightarrow$ Ca(OH)$_2$ + heat, 'heat' appears with the products, so heat is given out, making it exothermic.
3. The two decompositions (KClO$_3$ and CaCO$_3$ giving CaO + CO$_2$) require heating, i.e. heat taken in, hence endothermic.
4. The reaction written with 'heat' as a reactant absorbs heat and is also endothermic.
_Source: Balbharati (Maharashtra Board) Class 10 Science & Technology, Ch 3 "Chemical Reactions and Equations", p.55_
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