# 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> | + | <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

The rate of change of entropy of a thermodynamic system is defined as where where 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*_{g}, may be expressed as*c*_{pg}is the specific heat at constant pressure of that gas,*R*_{g}is its gas constant, and*T*and*p*_{g}are its temperature and pressure. The entropy of a liquid,*s*_{l};t7, is*c*_{l}is the specific heat of the liquid.