Equilibrium ionisation constants

Different equilibrium dissociation constant and equilibrium ionisation constant equations may then be derived with reference to the kinetic scheme (Scheme 8.16) on the basis of stasis, such as Equation (8.93), which dehnes an equilibrium dissociation constant acidic functional group 1, or 8.95 that defines the equilibrium ionisation constant K di for basic functional group 2 ... 

In contrast, equilibrium properties have been successfully discussed in terms of the field effect. Notable instances are those of the ionisation constants of saturated dibasic acids, - and of carboxyl groups held in... 

When substances ionise their neutral species produce positive and negative species. The ionisation constants are those constant values (equilibrium constants) for the equilibria between the charged species and the neutral species, or species with a larger number of charges (e.g. between mono and dications), l ese ionisation constants are given as pK values where pK = -log K and K is the dissociation constant for the equilibrium between the species [Albert and Serjeant The Determination of Ionisation Constants, A Laboratory Manual, 3rd Edition, Chapman Hall, New York, London, 1984, ISBN 0412242907]. 

K is the equilibrium constant at a particular temperature and is usually known as the ionisation constant or dissociation constant. If 1 mole of the electrolyte is dissolved in Vlitres of solution (V = l/c, where c is the concentration in moles per litre), and if a is the degree of ionisation at equilibrium, then the amount of un-ionised electrolyte will be (1 — a) moles, and the amount of each of the ions will be a moles. The concentration of un-ionised acetic acid will therefore be (1 — a)/ V, and the concentration of each of the ions cl/V. Substituting in the equilibrium equation, we obtain the expression ... 

Metzler and Snell (22) have reported the UV absorption spectra and ionisation constants of vitamin Bg group. The authors have calculated the equilibrium constants between dipolar ionic and uncharged neutral forms of the 3-hydroxy-pyridines investigated. 

AG° can also, of course, be defined in terms of Ka, the equilibrium constant written in terms of activities, a. [Note This symbol should not be confused with that for the acid ionisation constant, also Ka], In this present case the standard state defined for A G° is that associated with unit activities (a = 1) rather than with unit pressure ( P° = 1 bar), or in the case where gases are involved, with unit fugacities (/ = 1). We can then write that ... 

Ill] A. Albert and E. P. Serjeant The Determination of Ionisation Constants - A Laboratory Manual, 3rd ed., Chapman and Hall, London, New York, 1984. [112] D. D. Perrin, B. Dempsey, and E. P. Serjeant pK -Prediction for Organic Acids and Bases, Chapman and Hall, London, 1981. [113] A. Streitwieser, E. Juaristi, and L. L. Nebenzahl Equilibrium Carbon Acidities in Solution, in E. Buncel and T. Durst (eds.) Comprehensive Carbanion Chemistry, Part A, p. 323ff., Elsevier, Amsterdam, 1980. [114] J. H. Futrell Gaseous Ion Chemistry and Mass Spectrometry, Wiley-lnterscience, New York, 1986. [115] R. T. Mclver Chemical Reactions without Solvation, Scientific... 

In the case of an acid dissociation, the equilibrium constant for the reaction is termed Ka, and is called the ionisation constant, the dissociation constant or, sometimes, the acidity constant. The above equation can now be rewritten as... 

Scm moP, what is the fraction ionised at this concentration From this calculate the equilibrium concentrations of H30" (aq), CI2CHCOO (aq) and Cl2CHCOOH(aq), and from these calculate the ionisation constant for Cl2CHCOOH(aq). 

Let us consider the proton transfer from acetone to a series of bases [3] and compare the logarithm of the rate constant with the pK of the conjugate acid of the base. A linear relationship is observed (Fig. 1) which is an example of a Bronsted correlation. If we had plotted log kf (a measure of the free-energy difference between ground and transition state) versus log k /kf (a measure of the free energy of the reaction) it is clear intuitively that the transition state would be product-like for a slope of unity and reactant-like for zero slope. It is difficult to measure equilibrium constants such as in Eqn. 1 but ionisation constants are easily estimated (using pH-titration equipment for example) so that the majority of comparisons are with these. Inspection of Eqns. 1 and 2 shows that the only identities are the base and the acid comparison of oxonium ion with acetone and water with the conjugate base of acetone is doubtful. 

The self-ionisation constant of a molten carbonate is characterised by the equilibrium ... 

The ionisation constant cannot be measured experimentally since it is not possible to measure concentrations of ionised species in the reaction mass. Because of difficulties in experimentally distinguishing these species from the molecular ones, the ionisation reactions in Eq. (3.7.12) are ignored and K is calculated by considering the equilibrium of the amino-carboxylic reaction only. This K would be some combination of iT,- and K -, it is defined by the following equation. 

So far the four metal ions have been compared with respect to their effect on (1) the equilibrium constant for complexation to 2.4c, (2) the rate constant of the Diels-Alder reaction of the complexes with 2.5 and (3) the substituent effect on processes (1) and (2). We have tried to correlate these data with some physical parameters of the respective metal-ions. The second ionisation potential of the metal should, in principle, reflect its Lewis acidity. Furthermore the values for Iq i might be strongly influenced by the Lewis-acidity of the metal. A quantitative correlation between these two parameters... 

ApA < 1. In Fig. 2 the region of curvature is much broader and extends beyond — 4 < ApA < + 4. One explanation for the poor agreement between the predictions in Fig. 3 and the behaviour observed for ionisation of acetic acid is that in the region around ApA = 0, the proton-transfer step in mechanism (8) is kinetically significant. In order to test this hypothesis and attempt to fit (9) and (10) to experimental data, it is necessary to assume values for the rate coefficients for the formation and breakdown of the hydrogen-bonded complexes in mechanism (8) and to propose a suitable relationship between the rate coefficients of the proton-transfer step and the equilibrium constant for the reaction. There are various ways in which the latter can be achieved. Experimental data for proton-transfer reactions are usually fitted quite well by the Bronsted relation (17). In (17), GB is a... 

These systems were fully characterised in terms of the rates of the ionisations and the equilibrium constants the BIE work has been summarised more recently [51]. 

Since the reverse of the reaction Nl is the ionisation of the ester, the equilibrium position for any one system depends critically on the nature, especially the polarity, of the solvent, which determines the AHS terms. The accumulation of the necessary thermochemical data is essential to a rationalisation of the relation between cationic and pseudocationic polymerisations but the prevalence of the former at low temperatures and of the latter at high temperatures is surely related to the fact that the dielectric constant, and with it solvation energies, increases as the temperature of a polar solvent is reduced, so that decreasing temperature favours ionisation. 

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