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[a] While processes in isolated systems are never reversible, [3] cyclical processes can be reversible or irreversible. [4] Reversible processes are hypothetical or idealized but central to the second law of thermodynamics. [3] Melting or freezing of ice in water is an example of a realistic process that is nearly reversible.
A process is said to be physically reversible if it results in no increase in physical entropy; it is isentropic. There is a style of circuit design ideally exhibiting this property that is referred to as charge recovery logic , adiabatic circuits , or adiabatic computing (see Adiabatic process ).
For any irreversible process, since entropy is a state function, we can always connect the initial and terminal states with an imaginary reversible process and integrating on that path to calculate the difference in entropy. Now reverse the reversible process and combine it with the said irreversible process.
where a reversible path is chosen from absolute zero to the final state, so that for an isothermal reversible process Δ S = Q r e v T {\displaystyle \Delta S={Q_{rev} \over T}} . In general, for any cyclic process the state points can be connected by reversible paths, so that
Often, when analysing a dynamic thermodynamic process, the simplifying assumption is made that each intermediate state in the process is at equilibrium, producing thermodynamic processes which develop so slowly as to allow each intermediate step to be an equilibrium state and are said to be reversible processes.
The first part of the book starts by presenting the problem thermodynamics is trying to solve, and provides the postulates on which thermodynamics is founded. It then develops upon this foundation to discuss reversible processes, heat engines, thermodynamics potentials, Maxwell's relations, stability of thermodynamics systems, and first-order phase transitions.
For a particular reversible process in general, the work done reversibly on the system, ,, and the heat transferred reversibly to the system, , are not required to occur respectively adiabatically or adynamically, but they must belong to the same particular process defined by its particular reversible path, , through the space of thermodynamic ...
For reversible (ideal) processes, the area under the T–s curve of a process is the heat transferred to the system during that process. [1] Working fluids are often categorized on the basis of the shape of their T–s diagram. An isentropic process is depicted as a vertical line on a T–s diagram, whereas an isothermal process is a horizontal ...