An endothermic reaction is one that takes in light or heat energy. For example, the enthalpy of solution for acetic acid dissolving in water is negative so it uses heat and hence is exothermic The...
Well those would typically be called exothermic reaction, which could include any reaction in which heat was not added to start the reaction, like the addition of sodium to water, or the combination...
Endothermic is the opposite of exothermic. [PLEASE EXCUSE THE CAPS, I CAN'T SEE LOWER CASE WELL ENOUGH TO CHECK MY TYPING] ... THERE ARE SEVERAL FAMILIAR EXOTHERMIC REACTIONS, SUCH AS IN ADDING WATER...