AbstractThe calculation of the electric potential and the ionic concentrations in the neighhourhood of a monolayer containing fatty acids or other, partially ionized, organic acids is discussed in order to get a basis for the understanding of reaction rates in unimolecular layers. The systems tinder connsideration show several features allowing straightforward theoretical reasoning. It seems difficult however to reach a detailed description without further experimental study. Therefore a simplifying treatment using the well‐knownGouy‐Chapmanmethod is deemed to he acceptable at this stage to serve as a lead in experimental resea