Difference between revisions of "Entropy"

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<div class="definition"><div class="short_definition">A thermodynamic [[state variable]] denoted by ''S'' (''s'' denotes [[specific entropy]], entropy per  unit mass).</div><br/> <div class="paragraph">The rate of change of entropy of a thermodynamic system is defined as  <div class="display-formula"><blockquote>[[File:ams2001glos-Ee30.gif|link=|center|ams2001glos-Ee30]]</blockquote></div> where ''Q'' is the heating rate in a [[reversible process]] and ''T'' is [[absolute]] temperature. Integration  of this equation yields the entropy difference between two states. The entropy of an [[isolated  system]] cannot decrease in any real physical process, which is one statement of the [[second law  of thermodynamics]]. The [[specific entropy]] of an [[ideal gas]], ''s''<sub>''g''</sub>, may be expressed as  <div class="display-formula"><blockquote>[[File:ams2001glos-Ee31.gif|link=|center|ams2001glos-Ee31]]</blockquote></div> where ''c''<sub>''pg''</sub> is the [[specific heat]] at constant pressure of that gas, ''R''<sub>''g''</sub> is its [[gas constant]], and ''T'' and  ''p''<sub>''g''</sub> are its [[temperature]] and [[pressure]]. The entropy of a liquid, ''s''<sub>''l''</sub>;t7, is  <div class="display-formula"><blockquote>[[File:ams2001glos-Ee32.gif|link=|center|ams2001glos-Ee32]]</blockquote></div> where ''c''<sub>''l''</sub> is the specific heat of the liquid.</div><br/> </div>
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<div class="definition"><div class="short_definition">A thermodynamic [[state variable]] denoted by ''S'' (''s'' denotes [[specific entropy]], entropy per  unit mass).</div><br/> <div class="paragraph">The rate of change of entropy of a thermodynamic system is defined as  <div class="display-formula"><blockquote>[[File:ams2001glos-Ee30.gif|link=|center|ams2001glos-Ee30]]</blockquote></div> where ''Q'' is the heating rate in a [[reversible process]] and ''T'' is [[absolute]] temperature. Integration  of this equation yields the entropy difference between two states. The entropy of an [[isolated system|isolated  system]] cannot decrease in any real physical process, which is one statement of the [[second law of thermodynamics|second law  of thermodynamics]]. The [[specific entropy]] of an [[ideal gas]], ''s''<sub>''g''</sub>, may be expressed as  <div class="display-formula"><blockquote>[[File:ams2001glos-Ee31.gif|link=|center|ams2001glos-Ee31]]</blockquote></div> where ''c''<sub>''pg''</sub> is the [[specific heat]] at constant pressure of that gas, ''R''<sub>''g''</sub> is its [[gas constant]], and ''T'' and  ''p''<sub>''g''</sub> are its [[temperature]] and [[pressure]]. The entropy of a liquid, ''s''<sub>''l''</sub>;t7, is  <div class="display-formula"><blockquote>[[File:ams2001glos-Ee32.gif|link=|center|ams2001glos-Ee32]]</blockquote></div> where ''c''<sub>''l''</sub> is the specific heat of the liquid.</div><br/> </div>
 
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Revision as of 16:54, 25 April 2012



entropy

A thermodynamic state variable denoted by S (s denotes specific entropy, entropy per unit mass).

The rate of change of entropy of a thermodynamic system is defined as
ams2001glos-Ee30
where Q is the heating rate in a reversible process and T is absolute temperature. Integration of this equation yields the entropy difference between two states. The entropy of an isolated system cannot decrease in any real physical process, which is one statement of the second law of thermodynamics. The specific entropy of an ideal gas, sg, may be expressed as
ams2001glos-Ee31
where cpg is the specific heat at constant pressure of that gas, Rg is its gas constant, and T and pg are its temperature and pressure. The entropy of a liquid, sl;t7, is
ams2001glos-Ee32
where cl is the specific heat of the liquid.