Answer
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Work Step by Step
Compare Figure 29-8 (for hydrogen) to Figure 29-10 (for ATP formation).
The $H_2$ molecule has no activation energy. As the 2 separate hydrogen atoms move closer together, the PE initially falls. The hydrogen atoms can have no kinetic energy, and still move close enough to bond.
In contrast, the reaction to form ATP molecule has an activation energy. As ADP and the phosphate group move closer together, the PE initially rises. The two components need to have some initial kinetic energy in order to move close enough to bond. Part of the initial kinetic energy is released in forming
the ATP molecule, but some remains as the PE of ATP.
The other major difference in the diagrams is that the $H_2$ molecule’s potential energy is less than the potential energy of the 2 atoms when they are far apart.
In contrast, the ATP’s potential energy is greater than the PE of ADP and the phosphate group when they are far apart. This stored energy is released when the bond is broken, and this energy can initiate other chemical reactions.