Endothermic and Exothermic?Watch
Exothermic means that the reaction "gives out" thermal energy.
Thermal energy means heat.
Therefore a reversible reaction means that the reaction between the two or more chemicals both absorbs (takes in) and emits (gives out) heat. Reversible means that a reaction can do two things.
To get the reactants back by the product (back reaction), energy has to be spent again. Without that energy, the product cannot be 'divided' in the reactants.