Final answer:
In an exothermic reaction, the energy stored in the reactants before they are mixed is chemical energy. When the reaction occurs, this potential energy is released as thermal energy (heat) and/or kinetic energy (motion).
Step-by-step explanation:
In an exothermic reaction, the energy stored in the reactants before they are mixed is chemical energy. Chemical energy is a type of potential energy that is stored in the chemical bonds of a compound. When the reaction occurs, this potential energy is released as thermal energy (heat) and/or kinetic energy (motion).