Isobaric heat capacity in non-reacting and in reacting systems

The isobaric heat capacity in non-reacting and in reacting systems has been analysed. The isobaric heat capacity C-p in non-reacting systems depends o n continuous distribution of enthalpy levels, according to the statistical thermodynamic model. The heat capacity in non-reacting systems is measured by supplying heat to the system and is related to the distribution of molec ules either among enthalpy levels or among entropy configurations without a ny possibility of distinction. The isobaric heat capacity DeltaC(p,app) in reacting systems is related to changes in distribution of molecules among e nthalpy levels separated by well defined large differences DeltaH as assign ed by the model. Therefore, the isobaric heat capacity is apparent because it depends also on the heat intrinsically produced by the reaction inside t he system. The heat capacity DeltaC(p,app) produced by changes of temperatu re in differential scanning calorimetry experiments is bound to changes of association fraction alpha ((T)) inside the system. It is shown how the den aturation heat determined by integration of the experimental curve can be r eproduced by integration of the function of the association fractions in a two-state denaturation process. The treatment has been extended to macromol ecules constituted by different domains giving origin to more complex profi les at the denaturation.