Reaction in which heat is given out along with the products is called exothermic reaction:
Example:
1. Burning of methane gas releases a large amount of energy. Hence it is an exothermic reaction.
2. Reaction of calcium oxide and water
Reactions that absorb energy or require energy in order to proceed are called endothermic reactions.
Example :
(a) When ammonium chloride is dissolved in water in a test tube, the test tube becomes cold.
(b) Reaction of barium hydroxide with ammonium chloride.
