HEAT CAPACITY OF THREE-COMPONENT SYSTEMS CONTAINING AMMONIUM IODIDE, N-METHYLPYRROLIDONE AND WATER

Demidov M.P., Novikov A.N., Kostyleva E.I.,
Arngold V.A., Selina V.A., Gubina K.P.

Novomoskovsk Institute, Mendeleev University of Chemical Technology

301665, Novomoskovsk, Druzhby st., 8

In this work, the heat capacities C_p of solutions of ammonium iоdide in a mixed solvent MP-water were measured with high accuracy over the entire range of compositions at 298.15 K. Heat capacity measurements were performed on the LKB 8700 calorimetric unit with an error of 2·10^-3 J/g·K. On the basis of the data obtained, the apparent molar heat capacities of Ф_с were calculated, extrapolating the concentration dependences of which to the state of infinite dilution the standard partial molar heat capacities of ammonium iоdide in the mixed solvent MP-water at 298.15 K were determined. To separate the values $\overline{C_{p,2}^{{^\circ}}}$ of ammonium iodide into ionic components, we used our data on the iodide ion in MP and MP-water mixtures [1] and the additivity condition of partial molar quantities. The values $\overline{C_{p,i}^{{^\circ}}}$ are shown in the table.

Standard partial molar heat capacities $\overline{C_{p,i}^{{^\circ}}}$ of ammonium iоn
in the mixed solvent MP-water at 298.15

Compared with alkali metal ions, where the values $\overline{C_{p,i}^{{^\circ}}}$ increase monotonously, the dependence on the composition of the mixed solvent for the ammonium ion is extreme: at low concentrations of MP, a minimum is observed, and at high concentrations, a maximum. In the entire range of compositions of the MP-H₂O mixture, the values $\overline{C_{p,i}^{{^\circ}}}$ of NH₄⁺ are higher than those of alkali metal ions, and the inversion of values occurs with a lower content of MP. This indicates the complex nature of intermolecular interactions in the studied solutions, which is significantly influenced not only by the properties of the MP-water binary system, but also by the structural behavior of the ammonium ion.

1. Novikov A. N. // Russ. J. Phys. Chem. A . 2011. Vol. 85, N 9. Р. 1546–1549.

The research was carried out with the financial support of the Ministry of Science and Higher Education of the Russian Federation within the framework of the scientific project of the laboratory "Laboratory of Ion Materials" (LIM), project no. FSSM-2024-0006.