Question

How to tell whether reaction is exothermic or endothermic?

Answer 1

If heat is PRODUCED in a reaction,then the reaction is exothermic.

If heat is ABSORBED during the reaction, then the reaction is endothermic.

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Answer 2

If energy is released in a reaction in the form of heat , light , etc is known as exothermic reaction

And

If energy is required for the reaction to take place in the form of heat or light or electricity it is known as endothermic reaction