entropy change in reversible and irreversible process pdf

Entropy change in reversible and irreversible process pdf

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Entropy Changes in Reversible and Irreversible Processes

Entropy of reversible and irreversible processes

Entropy and the Second Law of Thermodynamics: Disorder and the Unavailability of Energy

13.4: Entropy Changes in Reversible Processes

So far we have been considering the change of entropy only in reversible-processes. Let us turn now to the problem associated with the change of entropy in irreversible processes and, in particular, in irreversible processes proceeding in an isolated system, which are of the greatest interest.

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Entropy Changes in Reversible and Irreversible Processes

Consider a system in contact with a heat reservoir during a reversible process. If there is heat absorbed by the reservoir at temperature , the change in entropy of the reservoir is. In general, reversible processes are accompanied by heat exchanges that occur at different temperatures. To analyze these, we can visualize a sequence of heat reservoirs at different temperatures so that during any infinitesimal portion of the cycle there will not be any heat transferred over a finite temperature difference. During any infinitesimal portion, heat will be transferred between the system and one of the reservoirs which is at.

You are expected to be able to define and explain the significance of terms identified in bold. A change is said to occur reversibly when it can be carried out in a series of infinitesimal steps, each one of which can be undone by making a similarly minute change to the conditions that bring the change about. For example, the reversible expansion of a gas can be achieved by reducing the external pressure in a series of infinitesimal steps; reversing any step will restore the system and the surroundings to their previous state. Similarly, heat can be transferred reversibly between two bodies by changing the temperature difference between them in infinitesimal steps each of which can be undone by reversing the temperature difference. The most widely cited example of an irreversible change is the free expansion of a gas into a vacuum. Although the system can always be restored to its original state by recompressing the gas, this would require that the surroundings perform work on the gas. Another example of irreversible change is the conversion of mechanical work into frictional heat; there is no way, by reversing the motion of a weight along a surface, that the heat released due to friction can be restored to the system.

In science, a process that is not reversible is called irreversible. This concept arises frequently in thermodynamics. In thermodynamics, a change in the thermodynamic state of a system and all of its surroundings cannot be precisely restored to its initial state by infinitesimal changes in some property of the system without expenditure of energy. A system that undergoes an irreversible process may still be capable of returning to its initial state. However, the impossibility occurs in restoring the environment to its own initial conditions. An irreversible process increases the entropy of the universe. Because entropy is a state function , the change in entropy of the system is the same, whether the process is reversible or irreversible.

Entropy of reversible and irreversible processes

Figure 1. The ice in this drink is slowly melting. Eventually the liquid will reach thermal equilibrium, as predicted by the second law of thermodynamics. There is yet another way of expressing the second law of thermodynamics. This version relates to a concept called entropy.

Entropy and the Second Law of Thermodynamics: Disorder and the Unavailability of Energy

Let a system change from state 1 to state 2 by a reversible process A and return to state 1 by another reversible process B. Then 1A2B1 is a reversible cycle. Therefore, the Clausius inequality gives:. If the system is restored to the initial state from 1 to state 2 by an irreversible process C, then 1A2C1 is an irreversible cycle.

Physics Stack Exchange is a question and answer site for active researchers, academics and students of physics. It only takes a minute to sign up. What difference between the two processes in molecular level is responsible for this change? It means an infinitesimal change in something as it undergoes a process. The something of interest here is a thermodynamic state function of a system, its surroundings, or the universe.

In order to calculate the change in entropywhen a system goes from one state a , to another b , we have to find a reversible path from a to b, and then calculate the integral:. Since we are at liberty choosing the reversible path, it is convinient to choose a path that gives an easy integration. From the isothermal expansion for an ideal gas from V 1 to V 2 , we have:.

Irreversible process

Из него выпрыгнули двое мужчин, оба молодые, в военной форме. Они приближались к Беккеру с неумолимостью хорошо отлаженных механизмов.

13.4: Entropy Changes in Reversible Processes

Оказавшись на улице, человек в очках в тонкой металлической оправе достал крошечный прибор, закрепленный на брючном ремне, - квадратную коробочку размером с кредитную карту. Это был опытный образец нового компьютера Монокль, разработанного ВМС США для проверки напряжения аккумуляторов в труднодоступных отделениях подводных лодок - миниатюрный аппарат, совмещенный с сотовым модемом, последнее достижение микротехнологии. Его визуальный монитор - дисплей на жидких кристаллах - был вмонтирован в левую линзу очков. Монокль явился провозвестником новой эры персональных компьютеров: благодаря ему пользователь имел возможность просматривать поступающую информацию и одновременно контактировать с окружающим миром. Кардинальное отличие Монокля заключалось не в его миниатюрном дисплее, а в системе ввода информации. Пользователь вводил информацию с помощью крошечных контактов, закрепленных на пальцах.

В интересах сохранения в тайне этого успеха коммандер Стратмор немедленно организовал утечку информации о том, что проект завершился полным провалом. Вся деятельность в крыле, где размещалась шифровалка, якобы сводилась к попыткам зализать раны после своего фиаско ценой в два миллиарда долларов. Правду знала только элита АНБ - ТРАНСТЕКСТ взламывал сотни шифров ежедневно. В условиях, когда пользователи были убеждены, что закодированные с помощью компьютера сообщения не поддаются расшифровке - даже усилиями всемогущего АНБ, - секреты потекли рекой. Наркобароны, боссы, террористы и люди, занятые отмыванием криминальных денег, которым надоели перехваты и прослушивание их переговоров по сотовым телефонам, обратились к новейшему средству мгновенной передачи сообщений по всему миру - электронной почте. Теперь, считали они, им уже нечего было опасаться, представ перед Большим жюри, услышать собственный записанный на пленку голос как доказательство давно забытого телефонного разговора, перехваченного спутником АНБ.

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