Chemical reaction that release energy in the form of heat, light and sound are called exothermic reaction.Reaction that observed energy or required energy in order to proceed is called endothermic reaction

Exothermic reaction :An exothermic reaction is a chemical reaction that releases energy in the form of light or heat.It gives net energy to its surroundings. That is, the energy needed to initiate the reaction is less than the energy that is subsequently released.

reactants → products + energyExamples of exothermic reactions:

Calcium oxide reacts vigorously with water to produce slaked lime(Calcium hydroxide) used in white washing releasing large amount of heat.

Burning of natural gas:when methane reacts with oxygen it releases vast amount of heat and cabon oxide and water.

2. Endothermic reaction :An endothermic reaction is any chemical reaction that absorbs heat from its environment.

reactants + energy → productsExample of endothermic reactions :

Melting of ice: Ice takes heat from the surroundings and turns in to liquid water.

Decomposition of Calcium Carbonate: When limestone is heated at above 900ºC it decomposes into quick lime and releases carbondioxide. CaCO3(limestone)-------------> CaO(quick lime) + CO2