State exothermic changes

Changes of State Solids, liquids, and gases can undergo various changes of state. The changes shown in green are exothermic, and those shown in blue are endothermic. 

Consider a first order, exothermic reaction (aA —> products) in a CFSTR having a constant supply of new reagents, and maintained at a steady state temperature T that is uniform throughout the system volume. Assuming perfect mixing and no density change, the material balance equation based on reactants is expressed as uC g = +... 

One notes that the proportionality constant, a, depends on the reaction energy, AEy. Therefore, Eq. (1.3) is not strictly a linear relation between activation energy change and reaction energy. In the extreme limit of high exothermicity of the reaction energy a = 0, and the crossing point of the two curves is at the minimum of curve Vj. In this case the transition state is called early. Its structure is close to that of the reactant state. 

We see that the total change in entropy is a positive quantity for both these spontaneous processes, even though one process is exothermic and the other is endothermic. When this type of calculation is carried out for other processes, the same result is always obtained. For any spontaneous process, the total change of entropy is a positive quantity. Thus, this new state function of entropy provides a thermod3mamic criterion for spontaneity, which is summarized in the second law of thermodynamics ... 

---