Diffusion and convection to an electrode with an irreversible reaction is allegedly a much simpler mass-transport problem than the same problem for a quasireversible reaction. This seems self-evident, since in the quasireversible case the mass transport of the product species has to be included, not just the reactant species. This leads to a coupled mass transport problem, and that has to be harder, right? Well, not necessarily. Under the common assumption that the diffusivities are equal, the quasireversible concentration profiles and current density can be trivially derived from the irreversible ones. One just replaces the forward rate constant by the sum of the forward and backward rate constants, scales the result and adds a constant. What could be simpler than that?

I show that this works under most of the convective diffusion situations encountered in electrochemistry. Of course there are some restrictions. On the other hand, for some cases the condition of equal diffusivities can be relaxed. I give some examples of where this is more than just a curiosity in relating known results in classic electrochemistry. In particular, it can lead to more efficient numerical analysis schemes.

[1] D.A. Harrington, Electrochim. Acta., 308, 152 (2015).