Molar Heat Capacity of AgI: Evaluation of the Cationic and Anionic Contributions from Thermoelectric Power Data

Abstract

Thermoelectric power data provide a useful tool for the evaluation of the thermodynamic properties of ionic species of both solid and molten electrolytes in equilibrium with electrodes of thermocells; however a previous evaluation of the heat of transport of the mobile ions is necessary. This is the case of AgI. whose standard modifications have been investigated with silver electrode thermocells some years ago. The interpretation of the thermoelectric power change at the melting point allows one to recognize that the heat of transport of the silver ions in the high conductivity bcc modification is practically the same as in molten Agl. This result has been used to evaluate the molar heat of the silver ions in the bcc phase from the corresponding thermoelectric power data reported in the literature. The analysis of the thermoelectric power change at the transition point, from the wurtzitic to the bcc phase, as well as a more speculative interpretation of thermoelectric power data obtained with iodine electrode thermocells, allows one to evaluate the molar heat of the iodide ions in the bcc modification of AgI. The summation of the ionic contributions so computed reproduces rather satisfactorily the trend of AgI molar heat data obtained with adiabatic calorimetry.