The kinetics of the homogeneous reduction of mercuric salts by-molecular hydrogen in aqueous solution have been examined over a wide range of solution composition, temperature and hydrogen partial pressure.
In perchlorate solutions, where Hg⁺⁺and Hg₂⁺⁺ are uncomplexed the kinetic results can be expressed by the equation:
-d[H₂]J/dt = k₁[H₂][Hg⁺⁺] + k₂[H₂][Hg₂⁺⁺] where k₁ = 4.2 x 10¹⁰ exp [-18100/RT] 1.mole⁻¹ sec.⁻¹ and k₂ = 1.2 x 10¹¹ exp [-20400/RT] 1.mole⁻¹ sec.⁻¹
It was concluded that the rate-determining process of the reaction involves the bimolecular interaction of one H₂ molecule with either Hg⁺⁺ or Hg₂⁺⁺ , i.e.,
Hg⁺⁺ + H₂ [symobal omitted] Hg + 2H⁺
Hg₂⁺⁺ + H₂ [symbol omitted] 2Hg + 2H⁺
The Hg atoms thus formed undergo further rapid reactions to yield the observed products (Hg₂⁺⁺ or metallic mercury) the nature of which is determined by •' thermodynamic considerations.
Mercuric complexes also reacted homogeneously with hydrogen but in most cases more slowly than the simple Hg⁺⁺ ions. The order of decreasing reactivity of the complexes, HgAc₂ > HgCl₂ > HgBr₂ > Hg(ethylenediamine)₂⁺⁺, is the same as the order of their increasing stability. This is attributed to the reduction of the electron affinity of Hg⁺⁺ through electron donation from the complexing ligand. The reactivity of mercuric complexes such as HgAc₂ and Hg(ethylenediamine)₂⁺⁺ is increased by anions such as 0H⁻, CO₃⁼, Ac⁻, etc., the influence of which increases in the same order as their basicity. This is attributed to stabilization, by the anions, of the H⁺ ions which are released in the rate-determining step of the reaction.
Some conclusions are drawn concerning the mechanism of heterogeneous activation of hydrogen by solid catalysts. / Applied Science, Faculty of / Materials Engineering, Department of / Graduate
| Identifer | oai:union.ndltd.org:UBC/oai:circle.library.ubc.ca:2429/40391 |
| Date | January 1956 |
| Creators | Korinek, George Jiri |
| Publisher | University of British Columbia |
| Source Sets | University of British Columbia |
| Language | English |
| Detected Language | English |
| Type | Text, Thesis/Dissertation |
| Rights | For non-commercial purposes only, such as research, private study and education. Additional conditions apply, see Terms of Use https://open.library.ubc.ca/terms_of_use. |
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