Basic research is needed to understand the thermodynamic properties of the interactions that are occurring in binary solutions such as tetra-n-butylammonium chloride-H2O (TBAC-H2O), and KCl-H2O. Water activity studies were performed on these binary systems as a function of solute concentration at specific temperatures between 20 and 45 degrees C. These water activities were converted to osmotic coefficients, phi, and the concentration dependence of these osmotic coefficients at a specific temperature were fit using either an equation developed by Scatchard, Rush and Johnson for electrolyte solutions or one that was modified by Leifer and Wigent for electrolytes that exhibit unusual thermodynamic behavior, such as the TBAC-H2O system. An experimental study was performed to determine the thermodynamic properties such as the osmotic and activity coefficients, free energy, enthalpy and entropy of the non-ideal portion of these systems ranging from 20 to 45 degrees C. For simple electrolyte systems, such as KCl-H2O it was observed that the osmotic and activity coefficients and total non-ideal free energy stay constant as a function of temperature. Further, it was observed that total non-ideal free energy is negative at all temperatures suggesting that the interactions within the solution are spontaneous. For the KCl-H2O system, the total non-ideal free energy due to water was positive, except at 20 degrees C at 1 and 2 molal KCl. This data suggests that the negative total non-ideal free energy observed is due to the contributions of total non-ideal free energy due to KCl, rather than the total non-ideal free energy due to water. For the TBAC-H2O system, the concentration dependence of the osmotic and activity coefficients exhibits a maximum around 2 molal due to semi-clathrate formation at lower temperatures but decreases gradually with increasing temperature. total non-ideal free energy becomes more stable (more negative) with increasing temperature and the negative values of total non-ideal free energy are found to be significantly affected by the contribution of total non-ideal free energy due to TBAC. The total enthalpy and entropy of this system are found to decrease with increasing temperatures.

Temperature dependence of the solution thermodynamics of the binary TBAC-H2O and KCl-H2O systems

ACS Spring Meeting 2021

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