NCERT Question 9 - Chapter 1 Class 10 - Chemical Reactions and Equations

What does one mean by exothermic and endothermic reactions? Give examples.

Answer

A chemical reaction in which a large amount of heat / energy is produced along with the products is called exothermic reaction.

For example, 

Calcium Oxide (Quick Lime) reacts with Water to produce Calcium Hydroxide (Slaked Lime) and Heat

CaO(s) + H ₂ O(l) → Ca(OH) ₂ (aq) + Heat

Since heat is produced / released in this reaction, this reaction is called an exothermic reaction

A chemical reaction in which a large amount of heat / energy is absorbed is called endothermic reaction.

For example, 

On heating of Calcium Carbonate (limestone) 

It decomposes into Calcium Oxide (Quick Lime) + Carbon Dioxide

CaCO ₃ (s)     →     CaO(s) + CO ₂ (g)

                        Heat

Since heat is absorbed in this reaction, this reaction is called an endothermic reaction.