Reaction energetics, determined from product

The properties of the reaction system near the transient region determine how the reactant evolves to the product side, and in a typical chemical reaction, reactions form short-lived intermediate reactive complex at the transition state region and finally decay into the final reaction products. The transition state region can be an energetic barrier, which separates the reactants from products, and in some cases after this barrier the reaction coordinate shows itself with a deep potential well, shown in Fig.4.la, which attracts the intermediate complex for a long time before it decays into the final products. The latter is always named as complex-forming reaction, and we shall not go into too much details in this kind of resonance, as recently it has been intensely reviewed by an elegant article [46]. We shall from now on only focus on the reactive resonance in direct reactions. 

When the reaction-rate constant cannot be determined from data on the reverse process, a reaction product must be observed, and its concentration related to that of the selectively energized reagent. If a spectroscopic technique can be used for this purpose, it will probably be necessary, and require little extension of the experiment, to measure the concentration of the product in each energetically accessible state. One then obtains detailed, or state-to-state, rate constants. 

In case 2, the lowest AG is that for formation of A from R, but the AG for formation of B from A is not much larger. System 2 might be governed by either kinetic or thermoifynamic factors. Conversion of R to A will be only slightly more rapid than conversion of A to B. If the reaction conditions are carefully adjusted, it will be possible for A to accumulate and not proceed to B. Under such conditions, A will be the dominant product and the reaction will be under kinetic control. Under somewhat more energetic conditions, for example, at a higher temperature, A will be transformed to B, and under these conditions the reaction will be under thermoifynamic control. A and B will equilibrate, and the product ratio will depend on the equilibriiun constant determined by AG. 

The process design of a PFR typically involves determining the size of a vessel required to achieve a specified rate of production. The size is initially determined as a volume, which must then be expressed in terms of, for example, the length and diameter of a cylindrical vessel, or length and number of tubes of a given size. Additional matters to consider are effects of temperature resulting from the energetics of the reaction,... 

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