When the chemical bond between the second and third phosphate groups of an ATP molecule is broken, energy is released.

Here's a breakdown:

* ATP (Adenosine Triphosphate): This is the primary energy currency of cells. It has three phosphate groups attached to an adenosine molecule.

* Bond Breaking: The bond between the second and third phosphate groups is a high-energy bond. When this bond is broken, the third phosphate group is released, leaving behind ADP (Adenosine Diphosphate).

* Energy Release: The breaking of this bond releases a significant amount of energy, about 7.3 kcal/mol (kilocalories per mole).

This energy is then used by cells to power various cellular processes, such as muscle contraction, nerve impulse transmission, and protein synthesis.