Equilibrium constants, chemical

Chemical reactions involving gases carried out in closed containers resemble in many ways the H20(/)-H20(g) system. The reactions are reversible reactants are not completely consumed. Instead, an equilibrium mixture containing both products and reactants is obtained. At equilibrium, forward and reverse reactions take place at the same rate. As a result, the amounts of all species at equilibrium remain constant with time. 

If we compare (8) with equation (2) of 148, putting const. = il in the latter, we see that the indeterminate constant of the equilibrium equation is now completely determined as the sum of the chemical constants of the interacting gases ... 

Sorption is defined as the bonding of a solute to a plastic. It is a physicochemical phenomenon related to the properties of the plastic and the chemical structure of the drug or other soluble components of the preparation. Interactions of this type can be determined by measuring the loss of the solute to the plastic at equilibrium under constant temperature conditions [11]. 

The Heisenberg Uncertainty Principle, describing a dispersion in location and momentum of material particles that depends inversely on their mass, gives rise to vibrational zero-point energy differences between molecules that differ only isotopically. These zero-point energy differences are the main origin of equilibrium chemical isotope effects, i.e., non-unit isotopic ratios of equilibrium constants such as K /Kj) for a reaction of molecules bearing a protium (H) atom or a deuterium (D) atom. 

At equilibrium at constant temperature and pressure, the chemical potential of each component must be the same in both phases. That is... 

Although these chemical effects are important in deciphering the genesis of ore minerals, it must be emphasized that the differences in the 8 8 values among coexisting condensed phases (hence the fractionation factor) at equilibrium are constant in each case because they depend only on T. 

One frequently encounters the case where the equilibrium dissociation constant (iQ, see above) is defined by microconstants with Tast rates on and off the receptor. However, any change in potency in a chemical series (affinity) must represent an increase in the on (k+i) rate or a decrease in the off rate (fe i). Occasionally, either by accident or design, the off rate is altered dramatically enough to redefine the receptor kinetics of the compound such that the rates influence the actual pharmacodynam-... 

At chemical equilibrium at constant temperature and pressure the Gibbs fiee ener of the system is a niinimum and AG = 0. Therefore, we have... 

He said that the vap. press, curve of liquid nitric oxide is somewhat anomalous, and this is attributed to polymerization of the molecules at low temp. The fact that the vapour density at atmospheric press, is quite normal at these temp, indicates, however, that the dissociation of the polymerized mols. is practically complete at this pressure. The high density of the liquid at its b.p., 1 -269, is cited as evidence in support of the view that the liquid mols. are associated. W. Nernst s value for the chemical constant is about 3-7 J. R. Partington s, 1-263 F. A. Hen-glein, and A. Langen, 0-92 and A. Eucken and co-workers gave 0-03 for the integration constant of the thermodynamic vap. press, equation and A. Eucken and F. Fried, 0-95 for the constant in the equilibrium equation for 2NO=N2-j-02. 

In terms of the chemical potential, the condition for chemical equilibrium at constant temp and pressure is ... 

Chemical equilibrium is achieved when chemical is distributed among environmental media (including organisms) according to the chemical s physico-chemical partitioning behavior. Thermodynamically, an equilibrium is defined as "a condition where the chemical s potentials (also chemical activities and chemical fugacities) are equal in the environmental media." At equilibrium, chemical concentrations in static environmental media remain constant over time. 

The triplets p, q, r are known as the stoichiometric coefficients of the chemical components in the formation equation of the complex, and are often quoted as subscripts next to the symbol used for the formation constant, which in this case is (3, so that the equilibrium formation constant would be defined as... 

According to thermodynamics, when a heterogeneous system is in equilibrium, at constant pressure and temperature, the chemical potential (p) of any given component must be the same in every phase. Therefore, if there is one component in three phases x, y and z and one of these phases, say x is referred to as standard phase, then this fret may be represented in the form of two equations ... 

Tab. 4.33 Calculation of equilibrium dissociation constants based on the drug s membrane concentration. (Reprinted from Tab. 3 of ref. 95, with permission from the American Chemical Society)...

In Eq. 1.3, i A = -1 for any A and uB = +1 for any B. Since Eq. 1.3 is an overall reaction, the assumption of constant stoichiometry underlying the definition of is not trivial, as discussed in Section 1.1. For example, at high pH, Eq. 1.28 would not always be applicable because of the influence of the reactions in Eqs. 1.1 and 1.5. On the other hand, at equilibrium, when the hydration reaction is described by Eq. 1.10, the application of Eq. 1.28 is possible. This fact serves to emphasize the difference between equilibrium chemical species that figure in thermodynamic parameters (e.g., Eq. 1.11) and kinetic species that figure in the mechanism of a reaction. The set of kinetic species is in general larger than the set of equilibrium species for any overall chemical reaction. 

Hartley, F. R., C. Burgess, and R. M. Alcock, Solution Equilibria, Wiley, New York, 1980. A comprehensive survey of equilibrium chemical speciationin ionic solutions, including methods of measurement, data analysis, and stability constants. 

A mixture of electrons, ions, and atoms forms a system similar to that which we considered in Chap. X, dealing with chemical equilibrium in gases. Equilibrium is determined, as it was there, by the mass action law. This law can be derived by balancing the rates of direct and inverse collisions, but it can also be derived from thermodynamics, and the equilibrium constant can be found from the heat of reaction and the chemical constants of the various particles concerned. The heats of reaction can be found from the various ionization potentials, quantities susceptible of independent measurement, and the chemical constants are determined essentially as in Chap. VIII. Thus there are no new principles involved in studying the equilibrium of atoms, electrons, and ions, and we shall merely give a qualitative discussion in this section, the statements being equivalent to mathematical results which can be established immediately from the methods of Chap. X. 

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