Equilibrium distribution between

Substitution on a cyclohexane ring does not greatly affect the rate of conformational inversion but does change the equilibrium distribution between alternative chair forms. All substituents that are axial in one chair conformation become equatorial on ring inversion, and vice versa. For methylcyclohexane, AG for the equilibrium... 

The isopiestic method is based upon the equality of the solvent chemical potentials and fugacities when solutions of different solutes, but the same solvent, are allowed to come to equilibrium together. A method in which a solute is allowed to establish an equilibrium distribution between two solvents has also been developed to determine activities of the solute, usually based on the Henry s law standard state. In this case, one brings together two immiscible solvents, A and B, adds a solute, and shakes the mixture to obtain two phases that are in equilibrium, a solution of the solute in A with composition. vA, and a solution of the solute in B with composition, a . 

The equilibrium distribution between the native conformation and the self-associating conformation ... 

When an aquifer is contaminated by a toxic, sparingly soluble, organic chemical that is readily attenuated, the acceptable concentration is usually determined to be in the low ppm to ppb range. The concentration of contaminant dissolved in groundwater is always related to the equilibrium distribution between the chemical retained on the... 

Contaminant volatilization from subsurface solid and aqueous phases may lead, on the one hand, to pollution of the atmosphere and, on the other hand, to contamination (by vapor transport) of the vadose zone and groundwater. Potential volatihty of a contaminant is related to its inherent vapor pressure, but actual vaporization rates depend on the environmental conditions and other factors that control behavior of chemicals at the solid-gas-water interface. For surface deposits, the actual rate of loss, or the pro-portionahty constant relating vapor pressure to volatilization rates, depends on external conditions (such as turbulence, surface roughness, and wind speed) that affect movement away from the evaporating surface. Close to the evaporating surface, there is relatively little movement of air and the vaporized substance is transported from the surface through the stagnant air layer only by molecular diffusion. The rate of contaminant volatilization from the subsurface is a function of the equilibrium distribution between the gas, water, and solid phases, as related to vapor pressure solubility and adsorption, as well as of the rate of contaminant movement to the soil surface. 

The concentration profile for a reactant A which must migrate from a drop or bubble into the continuous phase to react might be as shown in Figure 12-10. There is a concentration drop around the spherical drop or bubble because it is migrating outward, but, as with a planar gas-liquid interface in the falling film reactor, there should be a discontinuity in at the interface due to the solubility of species A and a consequent equilibrium distribution between phases. 

Let us consider the reaction between a typical hydrocarbon, C Hm, and D2. As a result of the exchange reaction, two kinds of equilibria will be established. There will firstly be an equilibrium distribution between the total amount of deuterium in the hydrocarbon and the total amount of deuterium in the hydrogen. Secondly, the relative amounts of the different isotopic species of hydrocarbon will be in equilibrium, and the same will apply to the different isotopic species of the hydrogen. In other words, the following interconversion equilibria for the hydrocarbon will be established,... 

The experimental determination of the film coefficients kL and kc is very difficult. When the equilibrium distribution between the two phases is linear, over-all coefficients, which are more easily determined by experiment, can be used. Over-all coefficients can be defined from the standpoint of either the liquid phase or gas phase. Each coefficient is based on a calculated over-all driving force Ac, defined as the difference between the bulk concentration of one phase (cL or cc) and the equilibrium concentration (cL or cc ) corresponding to the bulk concentration of the other phase. When the controlling resistance is in the liquid phase, the over-all mass transfer coefficient KLa is generally used ... 

Fast exchange, maintaining the singlet-oxygen equilibrium distribution between both compartments. The singlet oxygen will follow, in the... 

Analytical HPLC is based on the elution development, which means that a small volume of the sample to be analysed is introduced into the flowing mobile phase — eluent — at the top of the chromatographic column. Various sample compounds have different equilibrium distributions between the stationary and the mobile phases, so that each compound spends a different time in the stationary phase and zones containing individual sample components move along the column at different velocities. This leads to the separation of the sample components in the chromatographic column and eventually the individual compounds are eluted from the column at different times from the introduction (injection) of the sample. 

Contraiy to the above treatment it may be argued that it would he more correct to express the equilibrium distribution between the inner and outside particle surface by... 

Fig. 1 Expected equilibrium distribution between saliva or rumen contents and plasma of acids and bases of differing pKa. Concentration ratio is the ratio of the salivary or ruminal concentration to concentration free in the plasma, calculated separately for acids and bases, for saliva of pH 8.2 and rumen contents over a range of pH 5.5-6.5, assuming plasma is pH 7.4. (From Ref. f)...

According to Scheme 5 cis and trans products are formed direct photolysis produces I8a and 18b in a ratio 10 1, whereas triplet sensitization yields a product ratio of 1.4 1, which is nearly equal to what would be expected for an equilibrium distribution between the different rotameric biradicals. A biradical such as this, which gives different products depending upon its multiplicity, is said to exhibit a spin-correlation effect. 

In the ternary complex Fd (red) passes an electron to FNR forming FNR (sq). A proton is taken up from the solvent for the formation of the neutral semiquinone. The redox potential of the individual, isolated components [i.e., -430 mV for FNR(sq)/FNR and -420 mV for Fd(red)/Fd(ox)] would suggest a nearly equilibrium distribution between the respective redox states, but in actuality, the redox potential ofFd is shifted to between -440 to -500 mV, thus facilitating the transfer. In the absence ofFd (ox), transfer is very fast, being complete within 3 ms. 

For the actual user, the desire is to obtain well-resolved peaks in a short time period. How this might be done requires an understanding of how column properties, analyte equilibrium properties, and resolution are interrelated. To do this, first we will introduce a new term, a or the selectivity factor, which represents the equilibrium distribution between two analytes, A and B. 

This is essentially the same as the distribution coefficient and the chromatographic process consists essentially of thousands of dynamic equilibria. However, there is not sufficient time for the sample to reach fully its equilibrium distribution between the two phases. The sample remaining in the mobile phase is carried down to a fresh portion of the column where it moves onto the stationary phase from the mobile phase. As concentration of the solute in the mobile phase from this first portion decreases, solute in this region of the column moves back from stationary phase to mobile phase, in keeping with the distribution coefficient, and is carried down to the second portion of the column where once again equilibrium is (nearly) achieved. This does not take place as a series of discrete steps but as a continuous dynamic process (Fig. 6). 

Potential-Determining Ions. These are by definition (11) those species of ions which by virtue of their equilibrium distribution between the two phases (or by their equilibrium with electrons in one of the phases) determine the interfacial potential difference, that is, the difference in galvanic potential between these phases. 

This may be related to 50 per cent of the administered dose appearing in the urine at 6 hours which would lower the plasma concentration following establishment of an equilibrium distribution between the brain and the plasma. The influx and efflux of the drug from the brain appear to proceed at the same rate over 10 hours [177]. Plasma concentrations in excess of 01 tg/ml result in a decrease of the net tubular secretion of the drug, and a decreased urinary excretion may result in an increased biliary secretion. The distribution and excretion of the drug is strongly influenced by pH [177]. 

Some environmental phase distributions closely resemble distributions involving pure or chemically well-defined phases. For example, the equilibrium distribution between the gas and aqueous phase is a well-defined characteristic of a chemical, described by Henry s law constant or the air-water partition coefficient Kaw- Further, the influence of properties of the water phase such as the... 

Radon 222 is shaken out of the water and the discharge of an electroscope is measured in the gas phase following the establishment of equilibrium distribution between the aqueous and the gas phase. This simple, long-practised method is still proving its worth today. 

Retention of the solute is determined by the overall equilibrium distribution between the stationary and... 

Lipophilicity is an important physicochemical parameter for organic substances, related to their biological activity. According to 1993 International Union of Pure and Applied Chemistry (lUPAC) recommendations, the partition coefficient Po/w or Ko/v, is a measure of lipophilicity by determination of the equilibrium distribution between octan-l-ol and water, as used in pharmacological studies and in the assessment of environmental fate and transport of organic chemicals ... 

The separation of components in gas chromatographic processes is the result of equilibrium distribution between a mobile gas phase and a liquid or solid stationary phase. The partition of a component between two phases is described by the Nernst distribution law. 

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