Entropy and Irreversible Processes

Entropy and Irreversible Processes

1. In origin entropy is a magnitude of thermodynamics such as temperature, density, mass or volume. It is represented by the letter S and serves to explain why some physical processes happen in a certain way by measuring the degree of disorder of a system at the molecular level.

   • In any thermodynamic equilibrium system, different energy microstates coexist at a molecular level compatible with the general state of the system. Entropy, in essence, is a measure that calculates the probability of changes in the system as a function of the probability of its microstates.
     • Applied to a dynamic system, entropy is the measure that explains why, if we put a hot object next to a cold one, the cold gets hot and the hot gets cold. There is a possibility that it may happen the other way around (that the hot object gets even hotter and the cold gets even colder), but it is so small that it simply never happens because the energy tends to expand.
       • Additionally, the concept of entropy is also used to measure the probability of receiving a set of messages in an information environment.
         • Presentado por: Gustavo Adolfo Hoyos - William Fonseca

2. The processes can be classified as reversible and irreversible. The concept of reversible process allows us to recognize, evaluate and reduce irreversibilities in real processes in engineering.

   • The Second Law tells us that any process that reduces the entropy of the isolated system is impossible. Suppose that a process occurs within the isolated system and that we will call in the forward direction. If the change in the state of the system is such that the entropy increases for the process we call forward, then for the backward process (that is, for the change in reverse to the initial state) the entropy would decrease. This process in reverse is impossible for the isolated system, and therefore we say that the forward process is irreversible.
     • If a process occurs, however, in which entropy does not change (isentropic process) by the forward process, then also the backward process remains unchanged. Such a process can go in any direction without violating The Second Law. Processes of this type are called reversible. The fundamental idea of ​​a reversible process is that it does not produce entropy.
       • Entropy occurs in irreversible processes. All true processes (with the possible exception of current flow in superconductors) present a certain irreversible measure, although many processes can be adequately analyzed if they are assumed to be reversible. Some processes that are clearly irreversible are: the mixture of two gases, spontaneous combustion, friction, and the transfer of energy as heat from a body with higher temperature to a body with a lower temperature.
         • The recognition of irreversibilities in a true process is especially important in engineering. Irreversibility, or moving away from the ideal condition of reversibility, reflects an increase in the amount of unorganized energy at the expense of better organized energy. Organized energy (such as that of a lifted weight) is easily put into practical use; Disorganized energy (such as the random movements of molecules in a gas) requires `` forcing or restraining '' before it can be used effectively. The engineer constantly strives to reduce the irreversibilities of the systems to obtain a better performance of these.
           • Bibliography. http://www.sc.ehu.es/sbweb/fisica_/estadistica/termodinamica/segundo/segundo1.html http://www.profesorenlinea.cl/Ciencias/entropia.htm http://www.cie.unam.mx/~ojs/pub/Termodinamica/node82.html