# Entropy

From Glossary of Meteorology

## 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}is*c*_{l}is the specific heat of the liquid.

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