A relationship between the Nusselt number and the chemical conversion arising from an energetic reaction in fully developed laminar or turbulent flow through a heated or cooled tube is formulated by the speculative adaptation and extension of a closed-form solution for an idealized case. This relationship may be interpreted as an analogy between reaction and heat transfer. It has a wider scope than the classical analogies between momentum and heat transfer but is inferior to them in the sense that it incorporates an arbitrary coefficient whose dependencies have not yet been completely resolved. The analogy was derived for a single first-order irreversible equimolar homogeneous reaction (restrictions that can be relaxed) and neglects entrance effects and changes in density and viscosity. The primary and unique contribution of the analogy is the mathematical representation and functional explanation of the chaotic and gross variation of the Nusselt number resulting from the combination of an energetic reaction and compensatory heat exchange. (c) 2006 American Institute of Chemical Engineers AIChE J, 52: 3645-3657, 2006.