Mercury thermodynamic parameters

Tables I and II contain electrochemical kinetic and related thermodynamic parameters for several transition-metal redox couples gathered at the mercury-aqueous interface. These systems were selected since the kinetics can be measured accurately under experimental conditions where the diffuse-layer potentials, , are small and/or could be estimated with confi-...

Much has been written about solid metal electrodes, which have now largely displaced liquid mercury. Those most often used as redox ( inert ) electrodes for studying electron transfer kinetics and mechanism, and determining thermodynamic parameters are platinum, gold, and silver. However, it should be remembered that their inertness is relative at certain values of applied potential bonds are formed between the metal and oxygen or hydrogen in aqueous and some non-aqueous solutions. Platinum also exhibits catalytic properties. 

The separation of solvent effects on reactivities into constituent initial-state and transition-state effects by the use of appropriate kinetic and thermodynamic data has been successfully carried out for several organic reactions. Thus, for example, the solvolysis of t-butyl chloride and the Menschutkin reaction were treated in this manner some time ago a recent organic example is afforded by the solvolysis of isopropyl bromide in aqueous ethanol. For inorganic reactions, this approach was early used for reactions of tetra-alkyltin(iv) compounds with mercury(ii) halides. A more recent analysis of reactions of low-spin iron(n) complexes with hydroxide and with cyanide in binary aqueous mixtures was complicated by the need to make assumptions about single-ion values in such ion+ion reactions. Recent estimates of thermodynamic parameters for solvation of complexes of the [Fe(phen)3] + type are helpful in this connection. However, it is more satisfactory to work with uncharged reactants when trying to undertake this type of analysis of reactivity trends. A suitable system is provided by the reaction of [PtClaCbipy)] with thiourea. In dioxan-and tetrahydrofuran-water solvent mixtures, reactivity is controlled almost entirely... 

Bigoli, R, Deplano, R, Mercuri, M.L. et al. (1996) Evaluation of thermodynamic parameters for highly correlated chemical systems a spectrophotometric study of the 1 1 and 2 1 equilibria between E and l,l -methylenebis(3-methyl-4-imidazoline-2-thione) (mbit) and Ll -ethylenebis(3-methyl-4-imidazoline-2-thione) (ebit). Crystal and molecular structures of mbit-2l2 and ebit-2l2. J. Chem. Soc., Dalton Trans., 3583-3589. 

Two experimental systems have been used to illustrate the theory for two-step surface electrode mechanism. O Dea et al. [90] studied the reduction of Dimethyl Yellow (4-(dimethylamino)azobenzene) adsorbed on a mercury electrode using the theory for two-step surface process in which the second redox step is totally irreversible. The thermodynamic and kinetic parameters have been derived from a pool of 11 experimental voltammograms with the aid of COOL algorithm for nonlinear least-squares analysis. In Britton-Robinson buffer at pH 6.0 and for a surface concentration of 1.73 X 10 molcm, the parameters of the two-step reduction of Dimethyl Yellow are iff = —0.397 0.001 V vs. SCE, Oc,i = 0.43 0.02, A sur,i =... 

Figure 9. Plots of 0 vs.. cj (o o o and —) and (AG a)/RT vs., ( and —) due to ethylene glycol adsorption on a Hg electrode at concentrations 2, 1.6, 1.2, 1.0, 0.7, 0,5 and 0.2 mol dm (from top to bottom). Points are experimental data reprinted from J. Electroanal. them., 28, S, Trasatti, Effect of the Nature of the Supporting Electrolyte on the Thermodynamic Analysis of the Adsorption of Organic Substances on Mercury. Adsorption of Ethylene Glycol form 0.1 m Aqueous Solutions of Halides, p. 257, Copyright 1970, with permission from Elsevier Science. Curves were calculated from Eqs. (16), (21), and (23) using the parameters given in text.

The mechanisms of decomposition of zinc and mercury oxides were further studied in [18]. The rates of vaporization of ZnO and HgO in a vacuum were measured with the aim of subsequent thermochemical analysis of the decomposition products by the third-law method. The thermodynamic functions required for the calculation are given in Table 16.6, and the conditions and results of the experiments, in Table 16.7. In this book, as compared to [18], the refined calculation scheme was used the condition of congruent vaporization was taken into account and the molar enthalpy (parameter E) was calculated using Eq. 4.14. 

This section will survey adsorption phenomena of ions and neutral molecules on the surface of mercury in contact with aqueous solutions at equilibrium. We shall assume throughout that no electrochemical reaction takes place at the interphase under discussion and, therefore, use thermodynamic methods for the calculation of the desired parameters. The parameters that are of interest in the study of adsorption are the surface excess T and its dependence on the electrode potential and concentration of adsorbate in the bulk the dependence of the charge of the electrode on its potential is also of interest. We shall, therefore proceed to discuss that part of thermodynamics which is relevant to adsorption on electrodes and then consider adsorption of ions first and of neutral molecules second. 

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