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lecture 4

# lecture 4 - Reversibility A path is reversible if changes...

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Reversibility A path is reversible if changes from A to B and then back to A leave bothsystem and surround- ings unchanged. A natural or spontaneous or possible process will always lead to changes toward equilibrium and is thus irreversible. An unnatural or non-spontaneous or impos- sible process (away from equilibrium) will not hap- pen without external influence. For a process to be reversible it must be per- formed at equilibrium . At equilibrium the system does maximum work , and the minimum of work is needed to re- turn the system to the initial state. example problem Handout 9 1

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The Second Law and entropy, S Clausius “Heat cannot by itself flow from a cooler to a warmer body”. “The thermodynamic state function S measures ran- domness. For an isolated system , for any spon- taneous process, S increases” S (isolated system) increases. Examination of the “Carnot cycle” leads to the def- inition of the new state function, entropy dS = dq rev T (1) The second law gives criteria for spontaneity, or the direction a process will go.
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