ENDOTHERMIC AND EXOTHERMIC REACTIONS

Heat exchanger-like, multi-tube reactors are used for both exothermic and endothermic reactions. Some have as much as 10,000 tubes in a shell installed between tube sheets on both ends. The tubes are filled with catalyst. The larger reactors are sensitive to transient thermal stresses that can develop during startup, thermal runaways and emergency shut downs. 

Several types of continuous discharges are easily available in the laboratory. These are radio frequency, Townsend, coronas, glows (normal and abnormal), and arcs. Each system possesses special characteristics which in effect govern the motion of charged particles between the electrodes, and apart from a few special cases the systems are too complex to lend themselves to simple analytical description for studying ion-molecule reactions. Here, two of the latter systems—namely, coronas and glows—will be treated in detail in order to demonstrate their feasibility for studying both exothermic and endothermic reactions. 

Define exothermic and endothermic reactions. What is the sign of AH for an exothermic reaction An endothermic reaction ... 

Figure 3.3 The temperature dependence of AC0, AH0, and T AS0 over large temperature ranges the behaviour (A) for negative AS0, (B) positive AS0 and (C) variation of In K with 1/7" for exothermic and endothermic reactions.

Besides this exothermic reaction, a number of other (both exothermic and endothermic) reactions also occur in the POx reactor including the cracking reaction ... 

Figure 20.23. Exothermic and endothermic reactions using a catalysed plate reactor 33)...

In this and the previous section, we have focused on the role energy plays in chemical reactions. This is an area of science known as thermodynamics, which stems from Greek words meaning movement of heat. The concepts we addressed, such as exothermic and endothermic reactions and entropy, fit neatly in the laws of thermodynamics, which are paraphrased as follows ... 

The SMART process is a good example of how industry can use catalysis to combine exothermic and endothermic reactions, and thus save on energy costs while at the same time increasing chemical productivity. Currently, five commercial plants run this process, producing over 1.3 million metric tons of styrene per year. 

Parametric Study for Coupling Highly Exothermic and Endothermic Reactions... 

Kolios et al. [106] performed an extensive study revealing that coupling of exothermic and endothermic reactions is possible under safe and stable operation conditions only in catalytic wall reactors and not in coupled packed beds. In the latter case instability and thermal runaway of the reactor may occur. Additionally, the two... 

Show that both exothermic and endothermic reactions follow Le Chatelier s principle and moderate the effect of heat added to a reactive system at equilibrium. 

The lower the activation energy the faster the rate of reaction the higher the activation energy the slower the reaction. This is true for both exothermic and endothermic reactions. 

Figure 14.1 Exothermic and endothermic reactions and the estimation of ASsurroundings-...

The major conclusions from the above-described studies are consistent in the asymmetric mode of operation the reaction zones of the exothermic and endothermic reactions inherently repel each other, leading either to an extreme maximum temperature or to poor performance. A noncontinuous heat supply and production during every other semicycle cause obviously strong fluctuations of operation. Moreover, reasonable states of operation are attainable only with an excess of gas during the exothermic semicycle. This contradicts the condition of equal heat capacities for optimal heat recovery (see Section 1.2.1.1). For example, the heat loss in the case displayed in Fig. 1.9 is equal to the heat demand of the endothermic reaction. Different strategies have been assessed with regard to their potential to reduce hotspots during the exothermic semicycle and to improve thermal efficiency. 

A bidirectional fixed-bed reactor for coupling exothermic and endothermic reactions. 

O. Yu. Podyacheva, et al., A catalytic heat-exchanging tubular reactor for combining of high-temperature exothermic and endothermic reactions. Chem. Eng J., 2001, 82, 355-360. 

Figure 11. Temperature and concentration gradients in and around a catalyst particle for exothermal and endothermal reactions.

The first three types (pellets, extrudates and granules) are primarily used in packed bed operations. Usually two factors (the diffusion resistance within the porous structure and the pressure drop over the bed) determine the size and shape of the particles. In packed bed reactors, cooled or heated through the tube wall, radial heat transfer and heat transfer from the wall to the bed becomes important too. For rapid, highly exothermic and endothermic reactions (oxidation and hydrogenation reactions, such as the ox-... 

Mal tseva et al. investigated the decomposition of Ca(AlH4)2 by DTA experiments which showed several exothermic and endothermic reactions associated with hydrogen evolution [182]. From in situ X-ray diffraction studies and DSC analysis of solvent-free Ca(AlH4)2, it is evident that the decomposition proceeds in three steps (Eqs. (5.37)-(5.39)) [76] ... 

Explain in your own words the concepts of exothermic and endothermic reactions. The terms chemical bonds and heat of reaction should appear in your explanation. 

Explain in your own words the concepts of heat of reaction exothermic and endothermic reactions heat of formation combustion heat of combustion standard heats of formation, combustion, and reaction heating value of a fuel adiabatic flame temperature ignition temperature ignition lag lower and upper flammability limits and flash point of a fuel a flame blue and yellow flames flashback and detonation. 

Exothermic and endothermic reactions.—Here is another application of equation (6), made in 1852 by Favre and Silbermann. 

The quantity of heat set free by a system which undergoes a transformation does not depend solely upon the initial and final states, page 86.-32. Example from the study of perfect gases, 37.—33. Case in which the quantity of heat set free by a system depends solely upon the initial and final states, 88.—34. Utility, in chemical calorimetry, of the preceding law, 89.-35. Exothermic and endothermic reactions, 41.—36. Heats of formation under constant pressure and at constant volume, 44.—37. Case in which the two heats of formation are equal to each other, 45.— 38. General relation between the two heats of formation, 45.—39. Case in which the compound is a perfect gas, 46.—40. The distinction between the two heats of formation has small importance in practice, 46.—41. Infiuence of temperature on the heats of formation, 47.-42. Heat of formation referred to a temperature at which the reaction considered is impossible, 48.—... 

In theory, gasification processes can be designed so that the exothermic and endothermic reactions are thermally balanced. For example, consider reactions 2 and 5. The feed rates could be controlled so that the heat released balances the heat requirement. In this hypothetical case, the amount of oxygen required is 0.27 mol/mol of carbon, the amount of steam required is 0.45 mol/ mol of carbon, and the oxygen-to-steam molar ratio is 0.6 ... 

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