Exothermic processes defined

The scale-up of exothermic processes is greatly enhanced through the use of the coefficient of thermal stability. Kafarov [2] defined this as the ratio of the slope (tan ttj) of the line representing the heat removal (due to the heat transfer medium and changes in enthalpy) to the slope (tan ttj) of the line representing heat generation (by the reaction) at the intersection of the two lines when plotted on the T versus Q coordinates. This is expressed as... 

The coupling of SR with POX is termed autothermal reforming (ATR). The exact definition varies. Some define ATR as an SR reaction and a POX reaction that take place over microscopic distances at the same catalytic site thus avoiding complex heat exchanging (16). Others have the less restrictive definition that ATR occurs when there is no wall between a combined SR reaction and catalytic POX reaction. ATR is carried out in the presence of a catalyst that controls the reaction pathways and thereby determines the relative extents of the POX and SR reactions. The SR reaction absorbs part of the heat generated by the POX process reaction, limiting the maximum temperature in the reactor. The net result is a slightly exothermic process. 

Energy added to a system is defined as positive, and energy released from a system is defined as negative. A process in which energy is added to a system is said to be an endothermic process. A process in which energy is released from a system is said to be an exothermic process. 

Define the following terms, and illustrate each with a specific example (a) matter (b) energy (c) mass (d) exothermic process (e) intensive property. 

For endothermic reactions the problem can be solved by dividing the reactor into multiple stages, with intermediate heat exchangers, defining a multi-bed reactor. In exothermic processes, the intermediate cooling may be achieved by mean of heat exchangers or by injection of cold feed. A schematic illustration of a multi-bed reactor is shown in Fig 11.2. 

Thermal analysis methods are defined as those techniques in which a property of the analyte is determined as a function of an externally applied temperature. The sample temperature is increased in a linear fashion, while the property in question is evaluated on a continuous basis. This technology is used to characterize compound purity, polymorphism, solvation, degradation, and excipient compatibility. Thermal analysis methods are normally used to monitor endothermic processes (melting, boiling, sublimation, vaporization, desolvation, solid-solid phase transitions, and chemical degradation) as well as exothermic processes (crystallization and oxidative decomposition). Access... 

Figure IB. The DSC profile, on the other hand, shows two well-defined endothermic stages (i.e. 124 and ca. 216 °C) and two weak exothermic processes at 275 and ca. 384 °C. This indicates, in line with the thermal behaviour of Ni-Mo catalysts [3], that the partial thermal decomposition overlapped the combustion reaction because of an overstoichiometric excess of... 

SECTIONS 5.3 AND 5.4 When a gas is produced or consumed in a chemical reaction occurring at constant pressure, the system may perform pressure-volume (P-1/) work against the prevailing pressure of the surroundings. For this reason, we define a new state function called enthalpy, El, which is related to energy H = E + PV. In systems where only pressure-volume work is involved, the change in the enthalpy of a system, API, equals the heat gained or lost by the system at constant pressure AH = q, (the subscript p denotes constant pressure). For an endothermic process, AH > 0 for an exothermic process, AH < 0. 

Exothermic processes should supply all the heat requirements for the process. Related topic thermal pinch, Section 1.11. Based on the conservation of energy, the heat acquired/lost by a stream = the heat transferred to/from the stream. For sensible heat, q = mass flowrate (F) X heat capacity per unit mass (Cp) X AT = heat transferred = UA MTD. This is sometimes rearranged to define a thermal heat transfer unit, THTU, = AT/MTD = UA/F c. ... 

Define these terms thermochemistry, exothermic process, endothermic process. 

The general influence of temperature on chromatographic retention can be explained as follows. In order to be retained on the stationary phase, molecules need to transform from a state of very little order while floating in the mobile phase to a much more ordered immobilized state in the stationary phase. This is a process that implies a reduction in entropy. In order to make retention still an energetically favorable process, thermodynamics defines that it must release heat. Thus, retention in chromatography is typically an exothermic process. If the temperature is increased, exothermic processes escape from this constraint by shifting the equilibrium to the original side. This implies that temperature increase is accompanied by a shift to the desorbed state of the molecules and thus a lower retention. There are some rare exemptions to this rule (as always), but those are based on secondary equilibria that overrule the effect described earlier. 

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