Spontaneous process endothermic

If you analyze the four spontaneous endothermic processes mentioned previously, you ll see that each involves an increase in the randomness of the system. When ice melts, for example, randomness increases because the highly ordered crystalline arrangement of tightly held water molecules collapses and the molecules become free to move about in the liquid. When liquid water vaporizes, randomness further increases because the molecules can now move independently in the much larger volume of the gas. In general, processes that convert a solid to a liquid or a liquid to a gas involve an increase in randomness and thus an increase in entropy (Figure 17.3). 

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. 

How does the entropy of the surroundings change during an exothermic reaction An endothermic reaction Other than the examples cited in text, describe a spontaneous endothermic process. 

A spontaneous process occurs by itself, whereas a nonspon-taneous process requires a continuous input of energy to make it happen. It is possible to cause a nonspontaneous process to occur, but the process stops once the energy source is removed. A reaction that is nonspontaneous under one set of conditions may be spontaneous under a different set of conditions. 20.5 The transition from liquid to gas involves a greater increase in dispersal of energy and freedom of motion than does the transition from solid to liquid. 20.6 In an exothermic reaction, A5 r,. > 0. In an endothermic reaction, A5, rr < 0. A chemical cold pack for injuries is an example of an application using a spontaneous endothermic process. 20.8(a), (b), and (c) 20.10(a) positive... 

The formation of rust on iron is an exothermic and spontaneous reaction. The reverse reaction is endothermic and nonspontaneous. You might conclude that all exothermic processes are spontaneous and all endothermic processes are nonspontaneous. But remember that ice melting at room temperature is a spontaneous, endothermic process. Something other than AH plays a role in determining whether a chemical process occurs spontaneously under a given set of conditions. That something is called entropy. 

We have seen examples of endothermic processes that are spontaneous, such as the dissolution of ammonium nitrate in water (Section 13.1). We learned in our discussion of the solution process that the driving force for a spontaneous, endothermic process is an increase in disorder, or entropy, of the system. However, we have also encountered processes that are spontaneous and yet proceed with a decrease in the entropy of the system, such as the highly exo ermic formation of sodium chloride from its constituent elements. (Section 8.2) Spon-... 

When we look closely at the previous examples of spontaneous endothermic processes, they have one major feature in common in every case, the chemical entities— atoms, molecules, or ions—have more freedom of motion after the change. Put another way, after the change, the particles have a wider range of energy of motion... 

In each of the three spontaneous endothermic processes discussed here, the increase in entropy (AS > 0) outweighs the fact that heat must be absorbed (AH > 0), and each process is spontaneous. 

Self-Test 7.15B Can a nonspontaneous endothermic process with a positive 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). 

B All reactions that are both exothermic and cause an increase in entropy will be spontaneous, but the converse (choice A) is not true. Some spontaneous reactions are exothermic but decrease entropy and some are endothermic and increase entropy. Choice B is correct. The reverse reaction of a non-spontaneous reaction (choice C) will be spontaneous. Melting snow (choice D) requires heat. Therefore it is an endothermic process... 

A) The ice cube will not melt unless heat is added. Therefore, AH is positive, denoting an endothermic process. Liquid water has more freedom of movement and therefore will possess a greater entropy, so AS will be positive. This process occurs spontaneously, so AG must be negative. The temperature increases during this transformation. 

Endothermic process or reaction (A// > 0) with A5 > 0 -> Only entropy favors spontaneity. 

The system (consisting of the water, the solid NH4NO3, and the resulting hydrated NH4+ and N03 ions) absorbs heat from the surroundings as the endothermic process occurs. Nevertheless, the process is spontaneous because the system becomes more disordered as the regularly arranged ions of crystalline ammonium nitrate become more randomly distributed hydrated ions in solution (Figure 15-10). An increase in disorder in the system favors the spontaneity of a reaction. In this particular case, the increase in disorder overrides the effect of endothermicity. 

The spontaneous exchange of lowcharge cations on clays is an endothermic process. 

Frequently, when salts dissolve in water, the solution becomes warm. Such a process is exothermic. When other salts, such as ammonium chloride, dissolve in water, the solution becomes cold, indicating an endothermic process. Because endothermic processes are usually not spontaneous, why does the latter process proceed ... 

When the tension is removed, the stretched rubber band spontaneously snaps back to its original shape that is, AG is negative and -AG is positive. The cooling effect means that it is an endothermic process (AH > 0), so that TAS is positive. Thus the entropy of the rubber band increases when it goes from the stretched state to the natural state. 

However, in many other cases, the sign of AH is no help. An exothermic process occurs spontaneously under certain conditions, whereas the opposite, endothermic, process occurs spontaneously under other conditions. Consider the following examples of phase changes, dissolving salts, and chemical changes. 

What features common to the previous endothermic processes can help us see why they occur spontaneously In each case, the particles that make up the matter have more freedom of motion after the change occurs. And this means that their energy of motion becomes more dispersed. As we ll see below, dispersed means spread over more quantized energy levels. 

The endothermic process of forming a solution of salt (NaCl) and water is spontaneous at room temperature. Explain how this is possible in terms of the higher entropy of the ions in solution compared to that of ions in the solid. 

Memon G.Z. ef al. (2008) Watermelon peel Methyl parathion pesticide 60 min 24 pmol.g physic-sorption process, pseudo-first kinetic model spontaneous and endothermic process, possible regeneration and reuse of sorbents by methanol wash... 

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