A coupling reaction is the reaction in which two fragments are joined together to form a new compound.
Example- When phenol is reacted with a diazonium salt to form p-Hydroxyaxobenzene which is an orange dye.
These coupled reactions help ATP molecules to generate a common intermediate. Due to which ATP cleavage (transfer of Phosphate molecule from one ATP molecule to another ATP molecule) to form ADP + P.
By coupling the exergonic reaction of ATP hydrolysis with endergonic reactions, ATP is used by the cells to conduct any function by a mechanism known as phosphorylation, ATP donates the phosphate group to another molecule.
In coupled reactions, means free energy released for the exergonic reaction is greater than the endergonic reaction.