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Abstract  

A micro-combustion calorimeter was developed. The small energy equivalent (ca. 68 JK–1) of this calorimeter makes it possible to measure combustion energies of very small samples. The energy equivalent was determined by burning 2 mg of benzoic acid. The standard deviation of the mean energy equivalent was reduced to 0.014% in 5 experiments. The standard massic energy of combustion of salicylic acid and the standard deviation of the mean were determined to be –21871±5 J g–1, which agrees well with the literature values. The standard molar enthalpy of formation of salicylic acid was derived as –591.2±1.7 kJ mol–1.

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Abstract  

Standard enthalpies of formation of amorphous platinum hydrous oxide PtH2.76O3.89 (Adams' catalyst) and dehydrated oxide PtO2.52 at T=298.15 K were determined to be -519.61.0 and -101.3 5.2 kJ mol-1, respectively, by micro-combustion calorimetry. Standard enthalpy of formation of anhydrous PtO2 was estimated to be -80 kJ mol-1 based on the calorimetry. A meaningful linear relationship was found between the pseudo-atomization enthalpies of platinum oxides and the coordination number of oxygen surrounding platinum. This relationship indicates that the Pt-O bond dissociation energy is 246 kJ mol-1 at T=298.15 K which is surprisingly independent of both the coordination number and the valence of platinum atom. This may provide an energetic reason why platinum hydrous oxide is non-stoichiometric.

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