Exothermic reactions. See

The oxidation of the hydrocarbon to alcohol is an exothermic reaction (see Table 1.5). The heat of oxidation depends on the structure of the oxidized group. 

Truly isothermal operation of a tubular reactor may not be feasible in practice because of large enthalpies of reaction or poor heat transfer characteristics. Nor is it always desirable, as, for example, in the case of a reversible exothermic reaction (see Sect. 3.2.4). In an exothermic catalytic reaction, it may be necessary to provide adequate means for heat transfer to prevent the development of local hot-spots on which coking may occur and reduce the catalyst activity. An excessive temperature rise may also cause the catalyst particles to sinter, thereby reducing their surface area and causing an irreversible decrease in catalytic activity. 

The above model has been further explored to account for reaction efficiencies in terms of a scheme where nucleophilicities and leaving group abilities can be rationalized by a structure-reactivity pattern. Pellerite and Brau-man (1980, 1983) have proposed that the central energy barrier for an exothermic reaction (see Fig. 3) can be analysed in terms of a thermodynamic driving force, due to the exothermicity of the reaction, and an intrinsic energy barrier. The separation between these two components has been carried out by extending to SN2 reactions the theory developed by Marcus for electron transfer reactions in solutions (Marcus, 1964). While the validity of the Marcus theory to atom and group transfer is open to criticism, the basic assumption of the proposed model is that the intrinsic barrier of reaction (38)... 

How much heat must be removed for normal, or abnormally possible, exothermic reactions (see Chaps. 7,17, and 18)... 

The scanning or dynamic mode of operation ensures that the whole temperature range of interest is explored. This must be ensured also in adiabatic experiments, where it is essential to force the calorimeter to higher temperatures, in order to avoid missing an important exothermal reaction (see Exercise 2 in Chapter 4). 

This expression was established for zero-order reactions, but can also be used for other reactions, if the influence of concentration on reaction rate can be neglected. This approximation is particularly valid for fast and exothermic reactions (see Section 2.4.3). 

The amalgam emerging from the ends of the cells is converted on graphite into mercury, 50% sodium hydroxide solution and hydrogen in a strongly exothermic reaction (see Fig. 1.7-5, 1.7-6 and 1.7-7). 

The energy diagrams of an endothermic and exothermic reaction (See Skill 5.1a) are compared below. 

These compounds are built up out of formaldehyde and primary amines by condensation and trimerization in an exothermic reaction (see Fig. 24). 

It is important to note that, unlike changing the concentration or pressure, a change in temperature will also change the value of K. For endothermic reactions, an increase in temperature results in an increase in the concentration of products in the equilibrium mixture and therefore an increased fQ. The opposite will be true for exothermic reactions (see Table 7 7b). 

There is a widespread belief that exotic patterns of behaviour in chemical systems require either very complex kinetic mechanisms or non-isothermal influences. There have been many investigations of the single, irreversible, exothermic reaction [see e.g. 1 5] proceeding under well-stirred, open conditions (in a CSTR). By contrast, the isothermal systems [6] covered have tended to be rather specific enzyme rate-laws or reactions at surfaces. Models proposed for homogeneous, isothermal reactions include complicated schemes [7 58] such as the Brusselator and Oregonator . Table 1 lists some of the important historical landmarks of this subject. 

Exotbemiic Reactions. Rgure 11-3(a) shows the variation of the concentration equilitmum constant as a function of temperature for an exothermic reaction (see Appendix C). and Figure I t-3(b) shows the corresponding equilibrium conversion X, as a function of temperature. In Example 11-3. we saw that for a hrst-CHder reaction the equilibrium conversion could be calculated using Equation (El 1-3.13)... 

The difference in energy between the initial and final states is the reaction enthalpy. If the reaction is endothermic (see Figure 3.1a), the final level is higher than the initial level (A/7 > 0). For an exothermic reaction (see Figure 3.1b), the final level is lower than the initial level (A/f < 0). 

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