energy stored in the reactants breaking bonds of the reactants kinetic energy absorbed by the reaction potential energy absorbed by the reaction
I gave my students this multiple choice question: A teacher demonstrates a chemical reaction. A student observes that the test tube in which the reaction occurs becomes warm. What is the source of the thermal energy generated by the reaction?

Only one answer is correct among these 4 choices:
- energy stored in the reactants
- breaking bonds of the reactants
- kinetic energy absorbed by the reaction
- potential energy absorbed by the reaction

Could you tell me which one is correct?

energy stored in the reactants