AbstractEquilibria involving gaseous species over liquid or solid Au‐Dy and Ag‐Dy mixtures were investigated by high temperature mass spectrometry using Knudsen cells. The enthalpy changes of the reactions\documentclass{article}\pagestyle{empty}\begin{document}$$\begin{array}{*{20}c} {{\rm{MDy}}\;({\rm{g)}}\; \mathbin{\lower.3ex\hbox{$\buildrel\textstyle\rightarrow\over {\smash{\leftarrow}\vphantom{_{\vbox to.5ex{\vss}}}}$}} \;{\rm{M(g)}}\;{\rm{ + }}\;{\rm{Dy(g)}}\;{\rm{and}}} & {(1)} \\ {{\rm{MDy(g)}}\;{\rm{ + }}\;{\rm{M(g)}}\; \mathbin{\lower.3ex\hbox{$\buildrel\textstyle\rightarrow\over {\smash{\leftarrow}\vphantom{_{\vbox to.5ex{\vss}}}}$}} \;{\rm{M}}_2 ({\rm{g}})\; + \;{\rm{Dy(g)}}\;{\rm{(M}}\; = \;{\rm{Au,}}\;{\rm{Ag)}}} & {(2)} \\ \end{array}$$\end{document}could be obtained by applying the third law method. The following dissociation energies were computed (reactions (1)):\documentclass{article}\pagestyle{empty}\begin{document}$$\begin{array}{*{20}c} {\Delta H_0^0 ({\rm{AuDy)}}\;{\rm{ = }}\;{\rm{254}}\; \pm \;{\rm{20}}\;{\rm{kJ}}\;{\rm{mol}}^{ - 1} } \\ {\Delta H_0^0 ({\rm{AuDy)}}\;{\rm{ = }}\;{\rm{124}}\; \pm \;{\rm{19}}\;{\rm{kJ}}\;{\rm{mol}}^{ - 1}.} \\ \end{array}$$\end{document}The standard heats of formation, ΔH0f.298, of AuDy(g) and AgDy(g) have been derived as 402 ± 21 and 448 ± 19 kJ mol−1. The enthalpy changes of the reactions (2) are\documentclass{article}\pagestyle{empty}\begin{document}$$\begin{array}{*{20}c} {\Delta H_0^0 \;{\rm{ = }}\;{\rm{33}}{\rm{.9}}\; \pm \;18.8\;{\rm{kJ}}\;{\rm{mol}}^{ - 1} \;({\rm{M}}\; = \;{\rm{AU)}}\;{\rm{and}}} \\ {\Delta H_0^0 \;{\rm{ = }}\;{\rm{34}}{\rm{.3}}\; \pm \;{\rm{17}}{\rm{.4}}\;{\rm{kJ}}\;{\rm{mol}}^{ - 1} \;({\rm{M}}\;{\rm{ = }}\;{\rm{Ag)}}..} \\ \end{array}$$\end{document}The experimental values of the dissociation energies of AuDy(g) and AgDy(g) are compared to the values predicted by the Pauling model of a po