Spontaneous processes prediction

Spontaneous processes result in the dispersal of matter and energy, hi many cases, however, the spontaneous direction of a process may not be obvious. Can we use energy changes to predict spontaneity To answer that question, consider two everyday events, the melting of ice at room temperature and the formation of ice in a freezer. 

Fig. 25 The monoclonal antibody 26D9, generated to the jV-oxide hapten [67], catalysed the 6-exo-tet ring closure of [65] regioselectively to yield the disfavoured tetrahydropyran product [68]. This is a formal violation of Baldwin s rules, which predicts a 5-exo-tet spontaneous process to generate tetrahydrofuran derivative [66].

Thermodynamics deals with the interconversion of heat and other forms of energy and allows us to predict the direction and extent of chemical reactions and other spontaneous processes. A spontaneous process proceeds on its own without any external influence. All spontaneous reactions move toward equilibrium. 

By itself, ASmix is incapable of predicting spontaneity and randomness this is demonstrated in crystallization and helix formation that anomalously result in a high degree of order (-AS), but are nevertheless spontaneous processes more significantly driven by a loss of latent heat ( — AH). 

Therefore, unlike internal energy and enthalpy, entropy is easily used to predict the direction of a spontaneous process. Thus... 

Would you predict the formation of a dinucleotide from two nucleotides to be a spontaneous process ... 

What determines whether a process under consideration will be spontaneous Where does a spontaneous process end How are energy, volume, and matter partitioned between the system and surroundings at equilibrium What is the nature of the final equilibrium state These questions cannot be answered by the first law. Their answers require the second law and properties of the entropy, and a few developments are necessary before we can address these questions. We define entropy by molecular motions in Section 13.2 and by macroscopic process variables in Section 13.3. Finally, we present the methods for calculating entropy changes and for predicting spontaneity in Section 13.5. 

Would you predict the formation of a dinucleotide from two nucleotides to be a spontaneous process How can you justify the existence of nucleic acids in light of the second law of thermodynamics ... 

How can we predict what reactions will happen in living cells In a spontaneous process, the free energy decreases (AGis negative). In a nonspontaneous process, the free energy increases. 

The total entropy of a system and its surroundings always increases for a spontaneous process —this is the formal statement of the second law. The law provides a way of gaining an indication of the disorder or randomness of a system this is the entropy S. It also provides a means of predicting whether a process will occur spontaneously. Thus the change in entropy AS associated with a change in a system in terms of the heat absorbed by the system at constant temperature T is given by... 

How can we use the fact that any spontaneous process is irreversible to make predictions about the spontaneity of an unfamiliar process Understanding spontaneity requires us to examine the thermodynamic quantity called entropy, which was first mentioned in Section 13.1. In general, entropy is associated either with the extent of randomness in a system or with the extent to which energy is distributed among the various motions of the molecules of the system. In this section we consider how we can relate entropy changes to heat transfer and temperature. Our analysis will bring us to a profound statement about spontaneity that we call the second law of thermodynamics. 

When AH is negative, the reaction is exothermic, whereas a positive value of AH points to an endothermic reaction. What can we say about a reaction s spontaneity based on its enthalpy change If we were to stop and list spontaneous processes that we observe around us and then determine whether those processes are exothermic or endothermic, chances are that a majority would be exothermic. This implies that there is some relationship between enthalpy and spontaneity. The relationship is not exclusive, however. If you think for a moment you should be able to point out some endothermic reactions that obviously occur spontaneously. The melting of an ice cube at room temperature is one simple example. So at this point we might conclude that exothermic reactions seem to be preferred in some way. But clearly there must be things other than energy or enthalpy at work in determining whether or not a process is spontaneous. To develop a way to predict the spontaneity of a reaction, we must first introduce an additional thermodynamic state function—entropy. 

Gibbs free energy (G) (10.6) A thermodynamic state function that can be used to predict the direction of spontaneous change at constant temperature and pressure. AG = AH - TAS, and AG < 0 for any spontaneous process. 

Thus our definition of the second law has led to a function, G, which will always decrease to a minimum in spontaneous processes in systems having specified values of T and P. It is an extremely useful thermodynamic potential. All we have to do is to find a way to get measurable values of this function for all pure compounds and solutes, and to find how they change with T, P, and concentration, and we will then be able to predict the equilibrium configuration of any system by minimizing G. 

Laws of Thermodynamics The laws of thermodynamics have been successfully applied to the study of chemical and physical processes. The first law of thermodynamics is based on the law of conservation of energy. The second law of thermodynamics deals with natural or spontaneous processes. The function that predicts the spontaneity of a reaction is entropy. The second law states that for a spontaneous process, the change in the entropy of the universe must be positive. The third law enables us to determine absolute entropy values. 

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