Heat Capacity Characteristics of the Solvation of Ammonium Ions in Mixed Solvent N-Methylpyrrolidone–Water at 298.15 K

Values of standard partial molar heat capacity $${{\overline {C_{p}^{0}} }_{i}}$$ are determined along with changes $$\Delta \mathop {\text{.}}\nolimits_{{\text{solv}}} C_{{p{\text{,}}i}}^{0}$$ in heat capacity during the solvation of ammonium ions in a mixed MP–water solvent at 298.15 K. The value of $$\Delta \mathop {\text{.}}\nolimits_{{\text{solv}}} C_{{p{\text{,}}i}}^{0}$$ of ammonium ions is presented as the sum of four contributions: electrostatic, cavity formation, structural changes in the solvent, and specific ion-solvent interactions. Values of the contributions are calculated on the basis of experimental data and model representations. The dependences of the obtained values on the composition of the mixture are discussed in connection with the structure of the mixed solvent.