Endothermic processes defined

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) weight (b) potential energy (c) kinetic energy (d) endothermic process (e) extensive property. 

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... 

Molten gold poured into a mold solidifies at atmospheric pressure. With the gold defined as the system, is the solidification an exothermic or endothermic process ... 

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. 

Define these terms thermochemistry, exothermic process, endothermic process. 

The flammability of a polymer is an interaction of pyrolysis, ignition, combustion, flame propagation, and flame extinction processes. The processes are brought about by the heat exposure of the polymer. Pyrolysis is an endothermic process and involves softening, melting, discoloration, cracking, decompositirai, vaporization, etc. of the polymer and release of pyrolysis products. The boundary of the pyrolysis process on the surface of the polymer is defined as the pyrolysis front. Pyrolysis process is also defined as the gasification of the polymer. 

Enthalpies of phase transitions are formally defined for the endothermic process. Hence they are all positive numbers. But, because each process above occurs under the... 

DSC analysis has been defined as an analysis that determines the temperatures and the heat flow associated with transitions in materials as a function of time and temperature. This technique can provide qualitative and quantitative information on the physical and chemical changes including changes in enthalpy involving heat capacity variations, such as heat absorbed (endothermic processes) and heat release (exothermic... 

The first candidate in our search for a chanical potential might be enthalpy, which we defined in Chapter 6. Periiaps, just as a mechanical system proceeds in the direction of lowest potential energy, so a chanical system might proceed in the direction of lowest enthalpy. If this were the case, all exothermic reactions would be spontaneous and all endothermic reactions would not. However, although most spontaneous processes are exothermic, some spontaneous processes are endothermic. For example, above 0 °C, ice spontaneously melts (an endothermic process). So enthalpy must not be the sole criterion for spontaneity. 

Energy can be defined as the capacity to do work or generate heat. An exothermic process releases energy as heat. An endothermic process absorbs energy as heat. 

In order to exemplify the potential of micro-channel reactors for thermal control, consider the oxidation of citraconic anhydride, which, for a specific catalyst material, has a pseudo-homogeneous reaction rate of 1.62 s at a temperature of 300 °C, corresponding to a reaction time-scale of 0.61 s. In a micro channel of 300 pm diameter filled with a mixture composed of N2/02/anhydride (79.9 20 0.1), the characteristic time-scale for heat exchange is 1.4 lO" s. In spite of an adiabatic temperature rise of 60 K related to such a reaction, the temperature increases by less than 0.5 K in the micro channel. Examples such as this show that micro reactors allow one to define temperature conditions very precisely due to fast removal and, in the case of endothermic reactions, addition of heat. On the one hand, this results in an increase in process safety, as discussed above. On the other hand, it allows a better definition of reaction conditions than with macroscopic equipment, thus allowing for a higher selectivity in chemical processes. 

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