In this article single-step ET is viewed as a reversible first-order kinetic process between two chemical species i and j. In biological (i.e., protein network) applications a chemical species could be a redox-active metal cation or an amino acid . By reversible (or reversibly coupled) it is simply meant that the reverse reaction is modeled with nonzero rate in addition to the forward reaction. The exchange of charge is viewed as reversible in the thermodynamic sense only at infinite time when the rates of exchange are zero; at this point the charge concentrations [i] and [j] no longer change with time. Molarity units are used for sake of chemical convention, although electrical units could be equally employed (say charge units) as the first-order nature of the differential equation permits any units. Excluding network effects of other adjacent and coupled species, charge will (tend to) flow from i to j when j is at lower redox potential. Since this article investigates chemical networks the redox potential of a species is interpreted as its absolute standard Gibbs free energy. In making the analogy to an electric circuit, absolute Gibbs free energy is interpreted as a node voltage. Morever, distances between coupled pairs act as resistances to electron transfer. The semiclassical equation for the rate constants of reversible connection i kij --⇀ ↽-kji j is given by (swap i and j to obtain