The surface diffusion coefficient (D_s) of Au atoms in 0.5 M H₂SO₄ at 298 K has been determined from the time dependence of the surface roughness factor of electrodispersed Au electrodes in 0.5 M H₂SO₄. The value of D_s for 0.5 M H₂SO₄ is 5 × 10⁻¹⁴ cm² s⁻¹, a figure which depends considerably on the presence of adsorbable species in solution. Thus, the adsorption of pyridine produces a remarkable decrease of D_s, whereas the adsorption of Cl⁻ ion results in the opposite effect. The corresponding values of D_s are 1.2 × 10⁻¹⁴ cm² s⁻¹ for 0.5 M H₂SO₄ + 0.1 M pyridine, and 2.5 × 10⁻¹³ cm² s⁻¹ for 0.5 M H₂SO₄ + 5 × 10⁻⁴ M KCl. These results are interpreted through the influence of the adsorbate on the Au surface atom diffusion mechanism.Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas (INIFTA)Facultad de Ciencias Exactas