Chemical Changes and Reactions — CHEMISTRY STD 9 — Question
ICSE BoardEnglish MediumSTD 9CHEMISTRYChemical Changes and Reactions5 Marks
Question
Define exothermic and endothermic changes. Give two example in each case.
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Answer
Exothermic Reaction
The chemical reactions which proceed with the evolution of heat energy are called exothermic reactions.
Examples:
Carbon burns in oxygen to form carbon dioxide and heat energy is produced.
$C + O_2 → CO_2 +$ Heat
Water added to quick lime (calcium oxide), slaked lime (calcium hydroxide) is produced with a lot of heat energy.
$CaO + H_2O → Ca(OH)_2 +$ Heat
Endothermic Reaction
The chemical reactions which proceed with the absorption of heat energy are called as endothermic reactions.
Examples:
When nitrogen and oxygen are heated together to a particular temperature of about $3000^oC$, nitric oxide gas is formed.
$N_2 + O_2 + Heat → 2NO$
Calcium carbonate decomposes into carbon dioxide and calcium oxide when heated to a temperature of about $1000^oC.$
$CaCO_3 +$ Heat $→ CaO + CO_2$
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