Thermodynamic properties of common salts in aqueous solutions

Abstract

A relationship between the activity of hydrogen ions and charge activity in an aqueous solution has been developed in a previous study. That study also revealed that the potential energy of an aqueous solution can be obtained by multiplying the charge activity with electrostatic potential of the solution. In this study, negative potential energy equalling Gibbs energy of four common salt (NaCl, KCl, NaNO3 and KNO3) solutions were quantified using the charge activity. Then the entropies of those salt solutions were computed using the Gibbs energy, enthalpy, and the charge activity. Charge activities were computed using the pH of those solutions at room temperature. It was found that potential energy, Gibbs energy, enthalpy and entropy of a solution is related to the charge activity of a solution, not the ionic charge number as previously thought. When the concentrations of NaCl, KCl, NaNO3 and KNO3 increased in single solutions the entropies of those solutions tend to decrease allowing them to achieve orderly states leading the salt particles to crystalise. The findings of this study will lead to better understanding and utilization of thermodynamic properties during crystallization which is vital important in brine recovery.