I was comparing heat of formation numbers with specific heat values, and the numbers look really weird.
Take a typical example like magnesium fluoride. Its $\Delta H$ is -1124 kJ/mol and its heat capacity is almost certainly less than 0.1 kJ/mol K. Divide and you get at least 11000 Kelvins!
So the heat of formation doesn't seem to go into raising the temperature of the product. It can't be going into the surroundings either; otherwise the reaction would vaporize anything nearby. Where does it go, or what's wrong with my reasoning?
Edit: OK so let's not use a fluorine compound. Take aluminum nitride. -318 kJ/mol. Are we really going to suggest aluminum burns in nitrogen at over 3000 K?
Edit: Si3N4: -745 kJ/mol.
Edit: Regarding the article on adiabatic flame temperature: aluminum burns in oxygen at 4000 K. The $\Delta H$ of Al2O3 is -1680 kJ/mol. 1680/(4000-298) = 0.45 kJ/mol K. This would be a fantastic heat capacity whether we're talking constant pressure or constant volume.