Estimation of thermodynamic functions of the thermal dehydration of nickel and cobalt chloride hydrates by differential thermal analysis (DTA) method

Abstract

Thermodynamic functions of the thermal dehydration of nickel and cobalt chloride hydrates have been estimated by quantitative differential thermal analysis method. Both the salts undergo melting at temperatures below 100 degrees C, followed by stepwise dehydration in rapid succession within a relatively small range of temperature. The heats of dehydration of different steps have been estimated from the area covered by the corresponding endothermic DTA peaks, which, however, requires careful consideration as two consecutive steps sometimes tend to overlap. The enthalpy (Delta H) and entropy (Delta S) of dehydration have also been estimated either from evaporation of free water released from molten salt or from icelike structure of the water of hydration. The calculated and experimental values of these two functions agree well within the limits of experimental error. Using the experimental values of enthalpy and entropy changes, free energy changes (Delta G) for different steps of dehydration at the peak temperatures have been calculated.