Study of the Vaporization of Amalgams with a New Knudsen Cell — Mass Spectrometer System. Part II: The Compounds Mg5Hg3, Mg2Hg, Mg5Hg2, and Mg3Hg and the Formation Enthalpies of All Compounds of the Mg — Hg System

Abstract

AbstractEvaporation of the compounds Mg5Hg3(s), Mg2Hg(s), Mg5Hg2(s), and Mg3Hg(s) was studied using a Knudsen cell‐mass spectrometer system. They evaporate according to the equations2 Mg5Hg3(s) ⇄ Hg(g) + 5 Mg2Hg(s), (1)5 Mg5Hg(s) ⇄ Hg(g) + 2 Mg5Hg2(s), (2)3 Mg5Hg2(s) ⇄ Hg(g) + 5 Mg3Hg(s), and (3) Mg3Hg(s) ⇄ Hg(g) + 3 MgHg(s) (4)The Hg partial pressures of Eqs. (1) to (4) arelog(pPa) = (4973.1 ± 60.3) K/T + (9.886 ± 0.12) (440 ‐ 540 K),log(pPa) = (6605.6 ± 69.1) K/T + (10.91 ± 0.11) (499 ‐ 7110 K),log(pPa) = (7118.3 ± 116.5) K/T + (10.91 ± 0.19) (548 ‐ 9890 K), andlog(pPa) = (7502.3 ± 58.8) K/T + (11.29 ± 0.10) (525 ‐ 695 K).The enthalpy changes of reactions Eqs. (1) to (4) were determined by the second and third law method. Formation enthalpies in kJ mol−1 at 298 K were obtained as –60.5 ± 4.3 (MgHg2), –56.4 ± 1.7 (MgHg), –217.1 ± 7.3 (Mg5Hg3), –79.8 ± 2.8 (Mg2Hg), –166.0 ± 6.8 (Mg5Hg2), and –84.2 ± 4.0 (Mg3Hg) for the compounds given in parentheses. Gibbs energies of formation of these compounds are also given. Formation entropies are discussed.