Spontaneous process exothermic processes

Magnetic PANI/Fe O nanocomposites were prepared via emulsion polymerization to remove nitrate ions, [41] which gave linear correlation to Freimdlich isotherm with a pseudo-second-order kinetic mechanism. The optimum sorption condition was found to be a 4.0 g/L sorbent solution with a contact time of 10 min at pH = 7.0. PANI-doped ZnCl and CuCl were used for sodium dodecyl benzene sulfonate (SDBS) removal in a spontaneous and exothermic process [42]. Toxic metallic cations, such... 

The first visible sign of combustion is the ignition. It may arise from self-ignition when the combustible system is ignited by virtue of the spontaneous internal exothermic processes. In the other case, forced ignition occurs when the combustible system is ignited by an external ignition source. 

Explain why low temperatures are needed to make spontaneous an exothermic process that decreases... 

Fresh charcoal is a strong absorbent for gases, and this is an exothermic process. The heat generated can be enough to cause spontaneous ignition in some cases. Hence it is customaiy to age charcoal by exposure to air and thus cover the absorption sites with a layer of nitrogen gas. Larger molecules will desorb and replace smaller molecules, so the charcoal will still be effective as a decolorant or deodorizer. 

We see that the total change in entropy is a positive quantity for both these spontaneous processes, even though one process is exothermic and the other is endothermic. When this type of calculation is carried out for other processes, the same result is always obtained. For any spontaneous process, the total change of entropy is a positive quantity. Thus, this new state function of entropy provides a thermod3mamic criterion for spontaneity, which is summarized in the second law of thermodynamics ... 

Vinyl acetate is normally inhibited with hydroquinone to prevent polymerisation. A combination of too low a level of inhibitor and warm, moist storage conditions may lead to spontaneous polymerisation. This process involves autoxidation of acetaldehyde (a normal impurity produced by hy droly sis of the monomer) to a peroxide which initiates exothermic polymerisation as it decomposes. In bulk, this may accelerate to a dangerous extent. Other peroxides or radical sources will initiate the exothermic polymerisation. 

The equilibria of all reactions under such conditions are displaced toward exothermic processes, even those that lead to the formation of highly ordered systems. Furthermore, one should bear in mind the possibility of a kind of autoregulation of the predominant direction of such spontaneous reactions processes with a relatively small heat release (closer to resonance processes ) could proceed with higher probability and, as the complexity of the molecules formed increases, the probability of the dissipation of the evolved energy among the intramolecular degrees of freedom becomes more pronounced. Therefore it seems possible that at very low temperatures under the conditions of initiation by cosmic rays, even most complex molecules can be formed with a small, but still measurable, rate, and that slow exothermic low-temperature reactions can play some part in the processes of chemical and biological evolution. 

Self-Test 7.15A Can a nonspontaneous exothermic process with a negative AS become spontaneous if the temperature is increased ... 

G decreases for a spontaneous process, like the energy of a mechanical system. Since AG incorporates both driving forces for spontaneity—enthalpy (energy) decrease and entropy (disorder) increase—an endothermic process may be spontaneous if the increase in disorder is big enough to counteract the unfavorable enthalpy change, and a process that leads to increased order (negative AS) may be spontaneous if the process is sufficiently exothermic (negative AH). 

Fig. 11.5. Regimes for exothermic, endothermic, spontaneous, and non-spontaneous processes in exergy-enthalpy diagrams.

Chemical reactions, like the metathesis reaction that produces lead (II) iodide, can occur spontaneously, just like physical processes. It was once believed that only exothermic processes occurred spontaneously however, it has been shown that many endothermic reactions can occur spontaneously as well. Another factor that must be considered when determining the spontaneity of a reaction is entropy. 

B) The amounts are really meaningless in this problem. The key pieces of information are the words dissolved and that the temperature increases. Because the temperature of the system increases, the dissolving must be an exothermic process, meaning that AH < 0. The sodium hydroxide dissolves in solution, meaning that the crystalline lattice breaks apart into solvated ions. This is a much less orderly formation, which means the entropy has increased. Therefore, AS > 0 in this process. Because the dissolving occurs spontaneously, AG must be negative. 

Do you notice a correlation Iron rusting and methane burning are exothermic and spontaneous. The reverse reactions are endothermic and nonspontaneous. Based upon reactions such as these, some nineteenth-century scientists concluded that all exothermic processes are spontaneous and all endothermic processes are nonspontaneous. However, you need not look far for evidence that this conclusion is incorrect. For example, you know that ice melts at room temperature. That s a spontaneous, endothermic process. 

Exothermic process or reaction (A// < 0) with A5 > 0 —> Enthalpy and entropy favor spontaneity. 

Adsorption is a surface phenomenon. When a multi-component fluid mixture is contacted with a solid adsorbent, certain components of the mixture (adsorbates) are preferentially concentrated (selectively adsorbed) near the solid surface creating an adsorbed phase. This is because of the differences in the fluid-solid molecular forces of attraction between the components of the mixture. The difference in the compositions of the adsorbed and the bulk fluid phases forms the basis of separation by adsorption. It is a thermodynamically spontaneous process, which is exothermic in nature. The reverse process by which the adsorbed molecules are removed from the solid surface to the bulk fluid phase is called desorption. Energy must be supplied to carry out the endothermic desorption process. Both adsorption and desorption form two vital and integral steps of a practical adsorptive separation process where the adsorbent is repeatedly used. This concept of regenerative use of the adsorbent is key to the commercial and economic viability of this technology. 

If we assume that spontaneous processes occur so as to decrease the energy of a system, we can explain why a ball rolls downhill and why springs in a clock unwind. Similarly, a large number of exothermic reactions are spontaneous. An example is the combustion of methane ... 

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