Abstract
The reversibility definition emerging from Carnot’s ‘lost-work’ notion or, equivalently, from considerations of optimal efficiency and lack of dissipation is here qualified as a rational alternative to that which based on Planck’s constant total-entropy criterion resorts to either a sequence of equilibrium states or the action of infinitesimal forces for the definition of the reversible path.
Highlights
The reversibility definition emerging from Carnot‟s „lost-work‟ notion or, equivalently, from considerations of optimal efficiency and lack of dissipation is here qualified as a rational alternative to that which based on Planck‟s constant total-entropy criterion resorts to either a sequence of equilibrium states or the action of infinitesimal forces for the definition of the reversible path
Planck‟s entropy-based criterion for determining the reversibility, or lack of it, of any given process taking a system from an initial equilibrium state A to a final equilibrium state B finds formal representation in the following expression: ∆Stot[A → B] = Stot,B − Stot,A ≥ 0, where the equality applies to reversible processes and the inequality to all others
That Carnot‟s perspective of reversibility in terms of lost-work and associated notions encompasses the whole of the process i.e. the initial and final equilibrium states in addition to the intermediate steps, can be understood by realizing that no work can be lost if none can in principle be generated, situation arising in the absence of any driving force, i.e. at equilibrium
Summary
A process which can in no way be completely reversed is termed irreversible, all other processes reversible. Since the decision as to whether a particular process is irreversible or reversible depends only on whether the process can in any manner whatsoever be completely reversed or not, the nature of the initial and final states, and not the intermediate steps of the process settle it...Every physical or chemical process in nature takes place in such a way as to increase the sum of the entropies of all the bodies taking any part in the process. I.e. for reversible processes, the sum of the entropies remains unchanged This is the most general statement of the second law of thermodynamics. In reversible changes the total entropy at any given point along the process is identical in magnitude to that of the initial state. In irreversible changes the total entropy increases along the process acquiring a maximum value at the final equilibrium state
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