What must happen in order for a chemical reaction to be specifically classified as endothermic instead of exothermic is that energy is absorbed in the form of heat.
Chemical reactions can be exothermic or endothermic depending on whether it gives off or absorb energy (in the form of heat).
When energy is given off by a reaction, the temperature of the reaction vessel becomes warmer than the initial temperature before the reaction. Such a reaction is said to be exothermic.
For endothermic reactions, heat energy is absorbed from the surrounding. Thus, the reaction vessel appears colder when compared to the initial temperature before the reaction.
More on exothermic and endothermic reactions can be found here: https://brainly.com/question/4345448
