Classify the following chemical reactions as exothermic or endothermic:

A. Electrolysis of water

B. Burning of natural gas

C. Decomposition of calcium carbonate

D. Burning of magnesium ribbon in air

Exothermic reaction is reaction in which heat is generated during the reaction and endothermic reaction is one in which heat is absorbed from the surrounding during the reaction.

A. Electrolysis of Water

During the electrolysis of water, heat is required to break the water molecule and hence the reaction is endothermic.

B. Burning of natural gas

During the burning of natural gas heat is generated and hence it is an exothermic reaction.

C. Decomposition of calcium carbonate

To break calcium carbonate heat is required and hence it is an endothermic reaction.

D. Burning of magnesium ribbon in air

Burning of magnesium ribbon is a highly exothermic reaction and so much heat is generated that the ribbon gives off UV rays during the reaction.