The adsorption equilibrium constant Kads estimated from the isotherm slope can be used to calculate the Gibbs energy of adsorption using the equation: Negative values of the change in the Gibbs energy indicate that in a 0.05 M NaCl solution the adsorption of molybdate ions on the surface of AZ31-xLi alloys proceeds spontaneously and thermodynamically irreversibly. It suggests that adsorption occurs immediately after the injection of the inhibitor into the system, which is also supported by the g-DEIS data. Adsorption processes for which the change in the Gibbs energy is more negative than -20 kJ/mol are usually of a physical nature, while those with change in the Gibbs energy below -40 kJ/mol correspond to chemisorption . The values between -20 and -40 kJ/mol correspond to mixed type of adsorption. However, caution should be taken for this parameter due to the relatively high used concentrations of the inhibitor.