Dynamic equilibrium, definition

A triple point is a point where three phase boundaries meet on a phase diagram. For water, the triple point for the solid, liquid, and vapor phases lies at 4.6 Torr and 0.01°C (see Fig. 8.6). At this triple point, all three phases (ice, liquid, and vapor) coexist in mutual dynamic equilibrium solid is in equilibrium with liquid, liquid with vapor, and vapor with solid. The location of a triple point of a substance is a fixed property of that substance and cannot be changed by changing the conditions. The triple point of water is used to define the size of the kelvin by definition, there are exactly 273.16 kelvins between absolute zero and the triple point of water. Because the normal freezing point of water is found to lie 0.01 K below the triple point, 0°C corresponds to 273.15 K. 

A second principle applying to these model systems is derived from their colloidal nature. With the usual thermodynamic parameters fixed, the systems come to a steady state in which they are either agglomerated or dispersed. No dynamic equilibrium exists between dispersed and agglomerated states. In the solid-soil systems, the particles (provided they are monodisperse, i.e., all of the same size and shape) either adhere to the substrate or separate from it. In the liquid-soil systems, the soil assumes a definite contact angle with the substrate, which may be anywhere from 0° (complete coverage of the substrate) to 180° (complete detachment). The governing thermodynamic parameters include pressure, temperature, concentration of dissolved... 

In the log—log representation of the phase diagram, the dynamic equilibrium relation 19 (/cc[R][Y] = d[I]o) or apt] = 1 appears as a straight line with slope — 1. It starts at (p, rj) = (1/a, 1), and it is practically identical to r] for p > 1/a. The trajectory must closely follow t], and hence, there is a time range where the equilibrium relation is certainly valid. With increasing 1/a, the equilibrium line shifts to the right. It will not be reached at all when 1/a becomes close to b m. Consequently, one condition for the existence of the equilibrium is a2/b 1. Further, because p < 1, one has b > 1, and this implies the third condition a 1 by combination with the first. With the definitions 41, this yields eqs 20. 

A second way of defining the distribution constant results from considering a single solute molecule. Under the conditions of dynamic equilibrium, this single molecule spends some of its time in each phase. The time spent in the stationary phase relative to the time spent in the mobile phase is also given by the distribution constant. This definition forms the basis of the chromatography theory. 

The calculation of the L and M, etc. critical absorption frequencies presents very great difl culties, for, if we suppose that an electron is removed from the second or third pair of orbits, it leaves this pair of orbits unbalanced. Just what would happen in this case is not dear, and it would require an additional assumption in order to complete the calculations. Definite general conditions of the dynamic equilibrium have not yet been found. 

The maximum absorbance signal depends on the number of free atoms in the light path. These free atoms are in dynamic equilibrium with species in the flame they are produced continuously by the flame and lost continuously in the flame. The number produced depends on the original concentration of the sample and the atomization efficiency (Table 6.2). The number lost depends on the formation of oxides, ions, or other nonatomic species. The variation of atomization efficiency with the chemical form of the sample is called chemical interference. It is the most serious interference encountered in AAS and must always be taken into account. Interferences are discussed in detail in Section 6.4. Table 6.2 can be used as a guide for choosing which flame to use for AAS determination of an element. For example, A1 will definitely give better sensitivity in a nitrous oxide-acetylene flame than in air-acetylene, where hardly any free atoms are formed the same is true of Ba. But for potassium, clearly an air-acetylene flame is a... 

By definition, the pole flows are positive quantities, so the exchange reversibility is also always positive. It ranges from zero, meaning total irreversibility in the j direction, to infinite, meaning total irreversibility in the opposite direction. The peculiar value one corresponds to an exchange in dynamic equilibrium (equal flows in both directions) and a tolerance around this value delimitates a reversible regime (or quasireversible when the tolerance is large). 

It may also occur that the multilayer adsorption begins only at a definite relative pressure, P, as has been assumed in the modifications of the BET theory. In this case, the basic dynamic equilibrium equation of the cloud (C) model, Eq. (354), should be modified as... 

Equation (21) is not strictly valid for calculating the heat of micellization because certain assumptions made in its derivation do not hold here. The equation implies that the micelle is at equilibrium near cmc in a standard state [27,54]. However, micelles are not definite stoichiometric entities but aggregates of different sizes that are in dynamic equilibrium with themselves and surfactant monomers. The aggregation number may vary with temperature. An extended mass action model describes micellization as a multiple equilibrium characterized by a series of equilibrium constants (see Section 6.2). Because these equilibrium constants cannot be determined, the micellar equilibrium is usually described by... 

The elastic and viscoelastic properties of materials are less familiar in chemistry than many other physical properties hence it is necessary to spend a fair amount of time describing the experiments and the observed response of the polymer. There are a large number of possible modes of deformation that might be considered We shall consider only elongation and shear. For each of these we consider the stress associated with a unit strain and the strain associated with a unit stress the former is called the modulus, the latter the compliance. Experiments can be time independent (equilibrium), time dependent (transient), or periodic (dynamic). Just to define and describe these basic combinations takes us into a fair amount of detail and affords some possibilities for confusion. Pay close attention to the definitions of terms and symbols. 

Electrochemical cells may be used in either active or passive modes, depending on whether or not a signal, typically a current or voltage, must be actively appHed to the cell in order to evoke an analytically usehil response. Electroanalytical techniques have also been divided into two broad categories, static and dynamic, depending on whether or not current dows in the external circuit (1). In the static case, the system is assumed to be at equilibrium. The term dynamic indicates that the system has been disturbed and is not at equilibrium when the measurement is made. These definitions are often inappropriate because active measurements can be made that hardly disturb the system and passive measurements can be made on systems that are far from equilibrium. The terms static and dynamic also imply some sort of artificial time constraints on the measurement. Active and passive are terms that nonelectrochemists seem to understand more readily than static and dynamic. 

Static system The batch-wise employment of ion-exchange resins, wherein (since ion exchange is an equilibrium reaction) a definite endpoint is reached in which a finite quantity of all the ions involved is present. Opposed to a dynamic, column-type operation. 

It should be noted that in this definition a system that ends up having a self-assembled structure may also start far from equilibrium and may be dynamic until the final structure has been reached. 

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