Why is app such a good repository of potential energy?
The key ideas for this answer are to consider both the electrostatic repulsion of the phosphates and entropy.
Each phosphate brings in negative charges. the more phosphates, the more repulsion there is.
Entropy is found in the form of
1) numbers of molecules (1 in ATP vs 2 in ADP and Pi and 3 in AMP and 2 Pi.)
2) Resonance structures. More combinations of resonance structures are found in ADP and Pi than in ATP.