Question

What is called an endothermic reaction​

Answer 1

An endothermic process is any process with an increase in the enthalpy H (or internal energy U) of the system. In such a process, a closed system usually absorbs thermal energy from its surroundings, which is heat transfer into the system.

Answer 2

Reaction in which heat is absorbed is called an endothermic reaction.

Example : When ammonium chloride is dissolved in water an endothermic reaction takes place.