Think of it this way - there can be no endothermic change without a simultaneous exothermic change.

For example, if you put a cold spoon into a hot cup of coffee, there will be a flow of thermal energy from the hot coffee to the cold spoon, due to their temperature difference (delta T). Now, is this endothermic or exothermic? Both. The spoon is undergoing an endothermic change, and one consequence of that (not the only one) is an increase in temp. What about the coffee? Exothermic. The flow of thermal energy will stop when they reach thermal equilibrium (same temp, or delta T = 0)

A chemical reaction that is exothermic can be measured by surrounding it with a water bath, letting the water absorb the released energy, and keeping the reactants and products at constant temperature. Since the "calorie" is defined by the specific heat of water, the increase in the water temp can be used to quantify the amount of energy released by the reaction at constant T.

Without this "working fluid" (water) the reactants and products themselves can absorb the released energy and undergo an increase in temp.

Hope this makes sense.

sg