The free-energy change (ΔG) of the hydrolysis of ATP to ADP and Pi may vary considerably with variations in pH temperature atmospheric pressure and concentrations of reactants and products. The free-energy change (ΔG) of the hydrolysis of ATP to ADP and Pi is approximately -7.3 kcal/mole but it varies from species to species. The free-energy change (ΔG) of the hydrolysis of ATP to ADP and Pi is constant at -7.3 kcal/mole.