Thermodynamic evaluation of diffusion in isothermal and periodic regimes using Arrhenius linearization

This study evaluated the thermodynamic activation parameters associated with the diffusion process in systems operating under isothermal and periodic conditions, aiming to elucidate the influence of temperature and thermal regime on transport mechanisms. Diffusion coefficients were experimentally determined at temperatures of 20, 30, and 40 °C and analyzed using the Arrhenius equation to calculate the activation energy (Ea), enthalpy (ΔH), entropy (ΔS), and Gibbs free energy (ΔG). The results revealed thermally activated behavior, typical of diffusion processes that depend on overcoming energy barriers. The obtained Ea values were 29.082 kJ·mol⁻¹ for the isothermal regime and 29.863 kJ·mol⁻¹ for the periodic regime, indicating discrete differences in the energy required for diffusing species to reach the transition state. Activation enthalpies (ΔH) ranged from 26.477 to 27.416 kJ·mol⁻¹, reflecting the energetic content involved in the formation of the activated complex. Activation entropies (ΔS), negative in all cases (−0.253 to −0.259 kJ·mol⁻¹·K⁻¹), indicate a decrease in structural disorder during the process, suggesting a reorganization of species in the transition state. The Gibbs free energy (ΔG) increased with temperature, ranging from 101.585 to 106.958 kJ·mol⁻¹, a behavior consistent with endoenergetic diffusion processes in which the entropic contribution is unfavorable. Comparison between the isothermal and periodic regimes showed good agreement among the thermodynamic parameters, suggesting similar kinetic mechanisms. These results confirm the applicability of the Arrhenius equation for diffusion analysis and highlight the usefulness of the thermodynamic activation approach as a tool for understanding the energetic and entropic aspects of transport mechanisms in materials subjected to different thermal conditions.