Define exothermic and endothermic reactions. Give two examples of each.
Exothermic reactions: The chemical reaction in which heat is given out is called exothermic reactions. It causes rise in temperature. .
e.g. (i) When carbon bums in oxygen to form carbon dioxide, a lot of heat is produced.
C + O2 → CO2 + heat.
When water is added to quicklime a lot of heat is produced which boils the water.
CaO + H2O → Ca (OH)2 + Heat.
Endothermic reaction: A chemical reaction in which heat is absorbed is called endothermic reaction. It causes fall in temperature.
e.g. (i) When nitrogen and oxygen together are heated to a temperature of about 3000°C, nitric oxide gas is formed.
N2 + O2 + heat → 2NO (g)
(ii) Decomposition of calcium carbonate into carbon dioxide and calcium oxide when heated to a 1000°C.
CaCO3 + Heat → CaO (s) + CO2 (g)