State function reaction profile

Figure 2.42. Relative steady-state methanation activity profiles for Ni ( ), Co (A), Fe ( ), and Ru (O) as a function of gas-phase H2S concentration. Reaction conditions 100 kPa, 400°C, 1% CO/99%H2 for Co, Fe, and Ru, 4% CO/96% H2 for Ni.131 Reprinted with permission from Academic Press.

Figure 3.1 A reaction profile, showing how the thermodynamic and kinetic quantities are related. X can be any state function (enthalpy, Gibbs energy, entropy, volume, etc.).

It is very important therefore to have information on the thermodynamic parameters, in this instance AF. These can be measured directly by diiatometry or from the relationship d nK/dP)T= - V/RTf Since AF = -3.8 cm mol-, AF5 = -0.9 + 3.8 = 2.9 cm moF, Ref. 102. We can represent the progress of this and any other reaction pic-torially by a reaction profile, using the concept of the activated complex. The reaction profile shows, often in a qualitative but useful fashion, the change of any activation parameter (AG"", A//T AS"" Ref. 110 or AF"" Ref. Ill) as a function of the extent of the reaction (termed the reaction coordinate). Since each step in a reaction will have an associated transition state, and thus a separate reaction profile, we may have a continuous series of such profiles joining the reactants to the ultimate product. 

The Sn2 reaction in solution. We saw above the application of microsolvation to Sn2 reactions ([14, 15]). Let us now look at the chloride ion-chloromethane Sn2 reaction in water, as studied by a continuum method. Figure 8.2 shows a calculated reaction profile (potential energy surface) from a continuum solvent study of the Sn2 attack of chloride ion on chloromethane (methyl chloride) in water. Calculations were by the author using B3LYP/6-31+G (plus or diffuse functions in the basis set are considered to be very important where anions are involved Section 5.3.3) with the continuum solvent method SM8 [22] as implemented in Spartan [31] some of the data for Fig. 8.2 are given in Table 8.1. Using as the reaction coordinate r the deviation from the transition state C-Cl... 

These trends can be portrayed by a simple model [49]. The reaction profile is written as the simplest polynomial function containing a minimum and a maximum, representing ground and transition state, respectively (Figure 5.16) ... 

Fig. 1.3.1 Variation of the concentration (c) of a species as a function of the disttince from the electrode surface (x) in the case of a steady-state electrode reaction. 1 True concentration profiie 2 fictitious profile of Nernst. Thickness of diffusion layer (5) depends on the rate of stirring, while c(x = 0) depends on the overpotential...

The synthesis of high-oxidation-state molybdenum alkylidenes was reported by Schrock in 1987 [121]. Due to their improved tolerance towards functional groups (table) their better reaction profile and their lower costs well-defined molybdenum based initiators are now preferred over the related systems containing tungsten [122]. 

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