Spontaneous processes entropy

Entropy is a measure of disorder according to the second law of thermodynamics, the entropy of an isolated system increases in any spontaneous process. Entropy is a state function. 

Another statement of the second law is this in any spontaneous process, the entropy of the Universe increases (AS. > 0). This statement is general, and it applies to any set of conditions. It is not confined to the special case of constant temperature and pressure, as is the statement that the free energy decreases in a spontaneous process. Entropy changes are particularly important in determining the energetics of protein folding. 

Gibbs criteria of equilibrium, of course, are in agreement with the second law of thermodynamics, which gives evidence of the variation of entropy in spontaneous processes (entropy increase) but gives no explicit evidence on the state of equilibrium itself. 

The relationship between entropy change and spontaneity can be expressed through a basic principle of nature known as the second law of thermodynamics. One way to state this law is to say that in a spontaneous process, there is a net increase in entropy, taking into account both system and surroundings. That is,... 

Notice that the second law refers to the total entropy change, involving both system and surroundings. For many spontaneous processes, the entropy change for the system is a negative quantity. Consider, for example, the rusting of iron, a spontaneous process ... 

Key Terms enthalpy, H free energy of formation, AG standard entropy change, AS° entropy, S spontaneous process standard free energy change, AG° free energy, G... 

Second law of thermodynamics A basic law of nature, one form of which states that all spontaneous processes occur with an increase in entropy, 457 Second order reaction A reaction whose rate depends on the second power of reactant concentration, 289,317q gas-phase, 300t... 

Thermodynamic, second law The entropy of the universe increases in a spontaneous process and remains unchanged in a reversible process. It can never decrease. 

Equation (5.52) is the first of our criteria. The subscripts indicate that equation (5.52) applies to the condition of constant entropy, volume, and total moles, with the equality applying to the equilibrium process and the inequality to the spontaneous process. 

The change in Gibbs free energy for a process is a measure of the change in the total entropy of a system and its surroundings at constant temperature and pressure. Spontaneous processes at constant temperature and pressure are accompanied by a decrease in Gibbs free energy. 

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 ... 

In any spontaneous process, the total entropy increases A S tgta] > 0. ... 

In thermodynamics, entropy enjoys the status as an infallible criterion of spontaneity. The concept of entropy could be used to determine whether or not a given process would take place spontaneously. It has been found that in a natural or spontaneous process there would be an increase in the entropy of the system. This is the most general criterion of spontaneity that thermodynamics offers however, to use this concept one must consider the entropy change in a process under the condition of constant volume and internal energy. Though infallible, entropy is thus not a very convenient criterion. There have, therefore, been attempts to find more suitable thermodynamic functions that would be of greater practical... 

Notice that dephasing of the transverse magnetization does not affect Mz a T2 process involves no energy transfer but, being a spontaneous process, does involve an increase in the entropy of the spin system. 

Hence, for an isolated system, the entropy of the system alone must increase when a spontaneous process takes place. The second law identifies the spontaneous changes, but in terms of both the system and the surroundings. However, it is possible to consider the specific system only. This is the topic of the next section. 

The Helmholtz and Gibbs energies on the other hand involve constant temperature and volume and constant temperature and pressure, respectively. Most experiments are done at constant Tandp, and most simulations at constant Tand V. Thus, we have now defined two functions of great practical use. In a spontaneous process at constant p and T or constant p and V, the Gibbs or Helmholtz energies, respectively, of the system decrease. These are, however, only other measures of the second law and imply that the total entropy of the system and the surroundings increases. 

We now introduce the second law of thermodynamics a physicochemical process only occurs spontaneously if accompanied by an increase in the entropy S. By corollary, a non-spontaneous process - one that we can force to occur by externally adding energy - would proceed concurrently with a decrease in the energetic disorder. 

The total change in entropy is AY( 0iai), which must be positive for a spontaneous process. From Equation (4.8), we say... 

The number of moles decreases from 1.5 mol of gas to 1 mol. Assuming equivalent entropies per mole, the entropy decreases. AS will be negative, so we do not expect a spontaneous process. 

The first law of thermodynamics states that the total energy of the universe is constant. The second law of thermodynamics states, that in all spontaneous processes, the entropy of the system increases. Entropy is a measure of the dispersion of energy from a localized one to a more disperse one. It can be... 

The Second Law of Thermodynamics states that all spontaneous processes move in a way that increases the entropy (disorder) of the universe. 

For an isolated (adiabatic) system, AS > 0 for any natural (spontaneous) process from State a to State b, as was proved in Section 6.8. An alternative and probably simpler proof of this proposition can be obtained if we use a temperature-entropy diagram (Fig. 6.13) instead of Figure 6.8. In Figure 6.13, a reversible adiabatic process is represented as a vertical line because AS = 0 for this process. In terms of Figure 6.13, we can state our proposition as follows For an isolated system, a spontaneous process from a to b must lie to the right of the reversible one, because AS = Sb Sa> 0. 

Entropy is a thermodynamic quantity that is a measure of disorder or randomness in a system. When a crystalline structure breaks down and a less ordered liquid structure results, entropy increases. For example, the entropy (disorder) increases when ice melts to water. The total entropy of a system and its surroundings always increases for a spontaneous process. The standard entropies, S° are entropy values for the standard states of substances. 

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