Answer:
Hi Motomasa, you are correct that there is a bit of a misrepresentation, or at least a glossing-over, in the standard description of the function of ATP. The "energy-storing" capacity of ATP is NOT in the forming and breaking of the covalent phosphate to phosphate bonds. ATP -> ADP releases energy by two mechanisms. First because the process of hydrolysing the y-phosphate (the terminal phosphate) releases energy. And second because ATP and ADP are maintained out of equilibrium in cells. The action of utilizing an ATP brings the system closer to equilibrium, which releases energy.
There is a required energy input to break the phosphate to phosphate bond. This is the activation energy. However, the energy released upon hydrolysis and moving the system towards equilibrium are of greater magnitude than the activation energy input. I hope this helps!
