The output of heat flow and heat compensation calorimeters is proportional to the rate of all physical and chemical processes taking place.  The large sample size associated with microcalorimeters makes it feasible to study reactions in dilute solutions (1-10 mg/ml MW ~ 300) as well as in the solid state.  This is a powerful and rapid way to screen reactivity of compounds at different conditions including pH, oxidizing agents, cosolvent effects, etc. In the example shown note that under basic conditions the reaction was endothermic while it was exothermic in acid buffer.  This gives the chemist insight into what drives the degradation reaction (entropy versus enthalpy driven).
The same data can be plotted as the log of heat flow versus 1/T to obtain the apparent activation energy.  Note that at pH 10 there were multiple activation energies associated with the decomposition (i.e., non Arrhenius).