Why does ATP contains a large amount energy?

ATP is a molecule with three phosphate groups attached to a DNA base (A). the third and second phosphate are often removed in chemical reactions and the energy released from breaking these bonds is carefully channelled to catalyse other chemical reactions in the cell.

ATP is also kept away from equilibrium of its chemical reaction, meaning in the cells there are many more molecules of ATP products made when phosphates are removed to give ADP or AMP:

ATP <-----> ADP + Phosphate

ATP <-----> AMP + Di phosphate (2 phosphates)

By the cell maintaining ATP at high concentrations and ADP and AMP at low concentrations the energy released from breaking ATP down to ADP or AMP is much larger than if there were equal amounts of ATP, ADP and AMP. This is why ATP is said to contain energy, like pushing a Bowling ball to the top of a hill and then letting it roll down ATP releases energy when it is turned into its products.