ATP is an unstable molecule which hydrolyses to ADP + Pi and further AMP + Pi, when it is in equilibrium with water. The high energy of the molecule comes from the two high energy phosphate bonds. The bond between phosphate molecules in AMP and ADP are called phosphoanhydride bonds. These· phosphoanhydride bonds are energy rich and contain about 30.5 kJ/mol.
$ATP + H_2 O \to ADP + Pi \: \Delta - 30.5 kJ/mol$
$ATP + H_2O \to AMP+ Pi \: \Delta - 61 kJ/mol$