Quick bio question Watch
Hope this answers your question?
Yes you are correct, breaking bonds is an endothermic process; energy has to be absorbed for bonds to be broken. However, the Pi group reacts with water to form orthophosphate and ADP gains a hydrogen (is reduced) during this process. So the net energy in the system is exothermic, as the net energy from the bonds formed in the system is higher than the energy used to break them. Moreover, it is kinetically favourable for ATP to be hydrolysed to ADP, as the highly negative, polar phosphate groups mean the molecule is relatively unstable. So it is a very rapid reaction that can release a lot of energy. Coupled with the mechanisms to regenerate ATP, this explains why ATP is a very useful molecule for cells.
I've been taught in lectures that when the phosphate is broken off, there is increased resonance of the phosphate group double bond that releases energy and also there is repulsion between the negatively charged phosphates (one that is released and those on newly-formed ADP) that creates and releases energy