Please choose the correct answer to the 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?

Answer1: energy stored in the reactants Answer2: breaking bonds of the reactants Answer3: kinetic energy absorbed by the reaction Answer4: potential energy absorbed by the reaction

Answer format: answer1/answer2/answer3/answer4
Answer: answer1