Chemical Reactions — Question 13

Exothermic Reaction

A chemical reaction in which heat is given out is called an exothermic reaction.

Examples:

1. When carbon burns in oxygen, carbon dioxide is formed and a lot of heat is produced.
   C + O₂ ⟶ CO₂ + Heat
2. When water is added to quicklime, slaked lime is formed and along with it a large amount of heat energy is produced.
   CaO + H₂O ⟶ Ca(OH)₂ + Heat

Endothermic Reaction

A chemical reaction in which heat is absorbed is called an endothermic reaction.

Examples:

1. When nitrogen and oxygen gas are heated together to a temperature of about 3000°C, nitric oxide gas is formed.
   N₂ + O₂ $\xrightarrow[3000\degree\text{C}]{\text{heat}}$ 2NO
2. When calcium carbonate is heated at 1000°C, it decomposes to give calcium oxide and carbon dioxide.
   CaCO₃ $\xrightarrow[1000\degree\text{C}]{\text{heat}}$ CaO + CO₂