In this book, the incidence of the second law of thermodynamics on heat capacity is examined with respect to heat flux taking place in a thermodynamically irreversible manner, as well as with respect to irreversible heat capacity (CIR = QIR/T). In another study, the heat capacities of aqueous mixtures of monoethanolamine with piperazine were measured from (303.15 to 353.15) K with a micro-reaction calorimeter (µRC) at an interval of 5 K. The authors discuss how heat capacity is a significant thermodynamic quality because of its intrinsic significance and its connection with other thermodynamic properties like enthalpy, entropy and Gibbs energy. The closing study explores ho the excess partial molar heat capacity of the water in binary aqueous-solvent mixtures (W + S), CPWE, provides insight into water structure enhancement, if present.