The Thermochemistry of Inorganic Solids IV. Enthalpies of Formation of Compounds of the Formula MX a Y b

It is found that the standard enthalpies of formation Δf H ○ 298 of double salts of the type MX a Y b are related by a simple additivity relation to Δf H ○ 298 of their binary salts MX c and MY d . For divalent metals M this relation takes the form, Δf H ○ 298(MXY) = 1/2  Δf H ○ 298(MX2)+ 1/2  Δf H...

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Veröffentlicht in:Journal of physical and chemical reference data 1987-07, Vol.16 (3), p.467-470
Hauptverfasser: Hisham, Mohamed W. M., Benson, Sidney W.
Format: Artikel
Sprache:eng
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Zusammenfassung:It is found that the standard enthalpies of formation Δf H ○ 298 of double salts of the type MX a Y b are related by a simple additivity relation to Δf H ○ 298 of their binary salts MX c and MY d . For divalent metals M this relation takes the form, Δf H ○ 298(MXY) = 1/2  Δf H ○ 298(MX2)+ 1/2  Δf H ○ 298(MY2)+C, with C=−13.4 or −17.6 kJ/mol giving equally good fits to the data. From a lesser number of data for trivalent and tetravalent metals M, one finds again a simple additivity relation of the form Δf H ○ 298(MX a Y b ) =(a x/z)Δf H ○ 298(MX z/x ) +(b y/z)Δf H ○ 298(MY z/ y )+C, where x, y, and z are the formal valences of X, Y, and M, respectively, so that z=a x+b y, and C=0. For 16 divalent metal compounds average deviations are 5.5 kJ/mol with a maximum deviation of 10.7 kJ/mol. For eight trivalent metal compounds the average deviations are 13.9 kJ/mol with a maximum of 50.6 kJ/mol. For five tetravalent compounds, the average deviations are 3.5 kJ/mol with a maximum of 6.3 kJ/mol.
ISSN:0047-2689
1529-7845
DOI:10.1063/1.555801