This article proposes a phenomenological method for evaluating the effective laminar forced-convective heat transfer rate between a hot wall and a heated fluid in which a positive heat of reaction is absorbed due to an endothermic reaction related to decompositions of the fluid molecules into numerous species. To avoid not only complicacies of such phenomena due to multiple variables and properties but also non-linearities of property variations due to reaction advancement, the problem is divided into two idealized processes of state change based on a classical thermodynamic viewpoint in which the non-atomic continuum approach is validated. The proposed method derives a simple but meaningful relation for the augmentation ratio of the effective Nusselt number as a result. (C) 2010 Elsevier Ltd. All rights reserved.