Micromixing in Capillary Channels is a important aspect that applies to different processes, such as electro-assisted drug delivery, micro-electrophoretic separations, soil remediation among others. In these cases, the hydrodynamics of a system can considerably change the dispersion of solute inside a capillary channel, due effect of buoyancy driven type flows on effective parameters, i.e., effective dispersion coefficient and effective convective velocity. This contribution includes a reactive surface at the walls (first order) to analyze retardation effects. In this approach, explicit analytical expressions have been derived for the effective parameters as a function of the ambient temperature, skew temperature parameter and net mass flow. The spatial averaging method, in combination with the solute species continuity equation, has been use to determine the effect of buoyancy driven type flows on “effective parameters” and to predict the macroscopic behavior of the system in a rectangular geometry. Several illustrations are presented to demonstrate the “macromixing” and retardation effect caused by buoyancy and wall reaction respectively. Specific cases of effective dispersion coefficient and effective convective velocity trends as function of the Thiele modulus, Grashoff and Schmidt numbers are analyzed.