What happens to the energy released by an exothermic reaction?
The energy released in a reaction can take on a variety of forms. Some examples are listed below...
The most common form for the energy released would be heat. This is the case of burning a fuel for example. However, a large amount of the energy becomes visible light as well.
If the fuel in burned in the engine of an automobile, it produces heat, motion, sound and ultimately, electrical energy as well (through the spinning motion of the alternator).
The energy of the reaction in an electrochemical cell produces electric potential energy (but hopefully very little heat) as it supplies high-energy electrons to the anode of the cell.
Hopefully that gives you some idea of the variety of useful energy forms that can result from exothermic reactions.