Heats of reaction in the solid state and their relationship to Bloch-Zunger structural diagrams

We demonstrate that there is a simple relationship between the heats of solid-state reactions, $AB+CD\leftrightarrows AD+CB$ ($A,B$ from Groups I or II; $C,D$ from Groups VI and VII), and the positions of these compounds on Bloch-Zunger ($R_{\sigma },R_{\pi }$) structural sorting diagrams. The predictions of the model for these heats of reaction are far superior to those from a model based on the principal valence quantum numbers of the atoms involved.