A CAPACITANCE STUDY OF THE SILVER(I) COPPER DISPLACEMENT REACTION/

Metal displacement (cementation) reactions are usually diffusion contr olled and conform to first order kinetics. When a displacement reactio n is carried out in a batch reactor, positive deviations from a first order rate plot are commonly observed once the deposit becomes suffici ently thick. It has been suggested that these rate enhancements are th e result of changes in deposit structure resulting in increases in sur face area. Another theory argues that the rate enhancements are due to turbulence associated with increasing roughness of the deposit. In th is paper, an attempt is made to discriminate between these two possibi lities by measuring the capacitance of a copper electrode immersed in a silver(I) solution. It was found that no anomalous capacitance chang es were observed corresponding to the region in which rate increases w ere observed. This suggests that turbulence effects, rather than area effects, are responsible for the increased reaction rate. Capacitance measurements were also conducted for the reaction between silver(I) an d copper in the presence of cyanide which caused the silver to deposit in a thin uniform layer on the copper surface, thus blocking the disp lacement reaction. It was found that the capacitance changed very litt le with time under these circumstances.