Comment
Figure shows first heating and cooling cycle.@
Sulfidation reaction starts often during the process of evacuation of ampoule. Exothermic reaction ranges from 45 to 310Ž. First step of reaction, peak at 119Žioverlapping with mp. point of S). Second peak at 197Ž. Peritectic decomposition of CuS occurs at 507Ž(onset)@127.65J/g. In cooling stage, corresponding peak at 481Ž,@-126.3J/g.
The enthalpy of formation
@Product is hexagonal CuS.
Apparent enthalpy, ƒ’Hf= 4.8Kcal/mol. This is considerably low compared to other references. There is the possiblity that the reaction had started before DSC runs were carried out.