A chemical reaction in which thermal energy is released is exothermic.
Explanation:
In an exothermic reaction, the net heat energy that gets generated tends to be lesser than the heat energy required to initiate the reaction. The activation energy helps in removing the energy from the chemical bonds in the reactant.
The product in question has lesser heat and has more compactness after the reaction. The released energy in the process makes the surrounding warmer, such as a campfire that releases energy in form of heat and light into the surrounding.