Eine neue Methode zur Messung von temperaturabhängigen Partialdrücken in geschlossenen Systemen. Die Bestimmung der Bildungsenthalpie und -entropie von PtI2(s)

Determination of Temperature Dependent Partial Pressures in Closed Systems – a New Method. The Heat of Formation for PtI₂(s) A new method to determine temperature dependent partial pressures of gaseous species in equilibria with condensed phases in closed systems (silica ampoules) at temperatures up to 1000 °C and pressures p_i 0.01 < p_i < 10 bar is presented. It is based on the determination of the change of mass in the gasphase caused by solid-gas transition at higher temperatures of substances which are deposited at one end of the ampoule. The results of the measurements give informations about reaction mechanisms, enthalpies and entropies. The reliability of the method is demonstrated at the example of the system Pt/I₂. The heat of formation and the entropy of PtI₂(s) (δ_BH°(PtI₂(s), 298) = –51.4 kJ · mol^–1, S°(PtI₂(s), 298) = 119.3 J · K^–1 · mol^–1) are computed from experimental results. The heat of thermal decomposition of PtI₂(s) was reconsidered by Knudsen Mass Spectrometry.