Selectivity ratio definition

You don t need to memorize selectivity ratios, but you should understand the concepts Involved and the order of reactivity and selectivity for halogens. Definitely know the two reactions Combustion and hatogenatian. They ere both radical and exothermic. 

We quantify by-product formation with selectivity. There are various definitions for selectivity. One definition is based on yields it is the overall selectivity and is the ratio of product yield to by-product yield. Mathematically... 

Model parameters can also be used to compute indices, which reflect the relative importance of the predictors in the definition of the model itself. In particular, two indices, the variable importance in projection (VIP) [43] and the selectivity ratio (SR) [44] are often used in the ambit of latent variable-based calibration. VIP is a measure of how much the individual variables contribute to the definition of both the X- and the Y-spaces in PLS-modelling. 

FIGURE 10 Variable selection signal-like representation of variable importance in projection (A) or selectivity ratio (B), allowing to identify the portions of the profile most relevant for the definition of the model. 

Let us then consider an arbitrarily selected point in a pipe in winch gas and solid particles are flowing. The flow of the mixture of gas and solid parti cles need not be homogeneous, i.e., the concentration of particles may vary across the cross-section of the pipe. This means that the mixture ratio p. should generally be regarded as a function of position in the pipe, and therefore the definition, Eq. (14.1), should be replaced by... 

If, for the purpose of comparison of substrate reactivities, we use the method of competitive reactions we are faced with the problem of whether the reactivities in a certain series of reactants (i.e. selectivities) should be characterized by the ratio of their rates measured separately [relations (12) and (13)], or whether they should be expressed by the rates measured during simultaneous transformation of two compounds which thus compete in adsorption for the free surface of the catalyst [relations (14) and (15)]. How these two definitions of reactivity may differ from one another will be shown later by the example of competitive hydrogenation of alkylphenols (Section IV.E, p. 42). This may also be demonstrated by the classical example of hydrogenation of aromatic hydrocarbons on Raney nickel (48). In this case, the constants obtained by separate measurements of reaction rates for individual compounds lead to the reactivity order which is different from the order found on the basis of factor S, determined by the method of competitive reactions (Table II). Other examples of the change of reactivity, which may even result in the selective reaction of a strongly adsorbed reactant in competitive reactions (49, 50) have already been discussed (see p. 12). 

Attempts to determine how the activity of the catalyst (or the selectivity which is, in a rough approximation, the ratio of reaction rates) depends upon the metal particle size have been undertaken for many decades. In 1962, one of the most important figures in catalysis research, M. Boudart, proposed a definition for structure sensitivity [4,5]. A heterogeneously catalyzed reaction is considered to be structure sensitive if its rate, referred to the number of active sites and, thus, expressed as turnover-frequency (TOF), depends on the particle size of the active component or a specific crystallographic orientation of the exposed catalyst surface. Boudart later expanded this model proposing that structure sensitivity is related to the number of (metal surface) atoms to which a crucial reaction intermediate is bound [6]. 

The emission index in general is defined as the mass of pollutant emitted per unit mass of fuel consumed. In quasi-steady diffusion flames, this is the ratio of the mass flux of pollutant out of the flame to the mass rate of consumption of fuel per unit flame area. Depending on the application, it may be more desirable to consider only the flux of pollutant to the air or the sum of the pollutant flux to both air and fuel. The latter definition is selected here, and a pollutant balance for the flame then enables the emission index to be expressed as the ratio of the mass rate of production of pollutant per unit area to the mass rate of consumption of fuel per unit area. In terms of the mass rate of production of species i per unit volume cDj, the mixture fraction, and the magnitude of its gradient VZ, the mass rate of production of species i per unit area is... 

This is the definition of the enantiomeric ratio E, which indicates the selectivity of the enzyme for the fast reacting enantiomer (A ) relative to the slowly reacting enantiomer... 

Although the term selectivity is often used, there is no widespread agreement yet on an exact definition. If two competing reactions are unselective , a 50 50 product ratio would be obtained from an unbiased competition between the two. It might then be considered to have no selectivity. To convert this product ratio of unity into a numerical value of selectivity equal to zero, we take the logarithm of unity [40]. There are various other definitions of selectivity, and caution is needed when obtaining data from the published literature often, a logarithmic term is not used [41 ]. 

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