Arsenic compounds, thermochemical

There are no other reported thermochemical data for zirconium arsenate compounds. 

Thermochemical measurements have been made on a number of arsenic compounds. The heats of formation of trimethyl- and triphenylarsine have been used to calculate the mean dissociation energy of the As—C bonds in these compounds. The values found, 51.5 kcal/mole for the methyl compound and 60.3 kcal/mole for the other, are significantly different (506,507). 

We have essentially exhausted all of the directly measured enthalpies of formation of compounds containing carbon-arsenic, -antimony and -bismuth bonds. However, let us now make use of other thermochemical data and see what can be derived using some plausible estimates. And barring that, let us see what new enthalpies of formation would become available if only some new measurement were made. 

The Barin tables are far more complete in coverage than any of the sources described above. All of the natural elements and their compounds are included. In addition to the substance types listed in USBM Bull 677, the Barin tables include a large number of ternary oxides - aluminates, arsenates, borates, chromates, molybdates, nitrates, oxy-halides, phosphates, titanates, tungstates, selenates, vanadates, zirconates, etc. - as well as cyanides, hydroxides, complex silicates and inter-metallic compounds. The only substances not included by Barin, for which tables can be found elsewhere, are the ionized-gas species and a limited number of gas species important only at very high temperatures, which are listed in the JANAF tables. For each table Dr. Barin gives references for each of the major thermochemical values employed (enthalpy of formation and entropy at 298 K, and heat capacity). Like the USBM Bulletins, no attempt is made to discuss the choice between conflicting data sources. 

Many analytes may form volatile species with other elements in the sample, for example, halides, or be present in compounds that exhibit high-vapor pressures at relatively low temperatures (mercury, arsenic, selenium, organometallics). Such compounds may be volatilized and swept from the tube, in molecular form, prior to the atomization step. These losses can be dealt with by adding a large excess of a reagent (a modifier) to change, in situ, the thermochemical behavior of the analyte and the matrix. 

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