Question

- In the opposite case, as the energy of the molecules decreases, the motion of the molecules Decreases. Where does the extra energy go?

Answer 1

Answer: It gets wasted in various forms.

Explanation: The most common way of this energy being wasted is called "waste heat".

Waste heat is the unused heat given to the surrounding environment (in the form of thermal energy) by a heat engine in a thermodynamic process (like a chemical reaction as you said) in which it converts heat to useful work.