When does coupling occur (when energy is released)?

In Physics coupling occurs when the energy released by an exergonic reaction is used to drive an endergonic reaction. Exergonic reactions are reactions that lose energy as the process takes place while endergonic reactions are reactions that require energy to be driven.

Am example of an exergonic reaction is cellular respiration and an example of a endergonic reaction is photosynthesis. The coupling of the two reactions can work to the advantage of the reactions to give them enough drive to be completed.