Editing Standard molar entropy (section)

==Chemistry==
The standard molar entropy of a gas at [[Standard temperature and pressure|STP]] includes contributions from:<ref>{{cite book|last=Kosanke|first=K.|title=Pyrotechnic chemistry|publisher=Journal of Pyrotechnics|year=2004|isbn=1-889526-15-0|chapter=Chemical Thermodynamics|page=29}}</ref>

* The [[heat capacity]] of one mole of the solid from 0{{nbsp}}K to the [[melting point]] (including heat absorbed in any changes between different [[crystal structure]]s).
* The [[latent heat of fusion]] of the solid.
* The heat capacity of the liquid from the melting point to the [[boiling point]].
* The [[latent heat of vaporization]] of the liquid.
* The heat capacity of the gas from the boiling point to room temperature.

Changes in entropy are associated with [[phase transitions]] and [[chemical reactions]]. [[Chemical equations]] make use of the standard molar entropy of [[reactants]] and [[Product (chemistry)|products]] to find the standard entropy of reaction:<ref>{{cite book|last1=Chang|first1=Raymond|last2=Cruickshank|first2=Brandon|title=Chemistry|publisher=[[McGraw-Hill Higher Education]]|year=2005|isbn=0-07-251264-4|chapter=Entropy, Free Energy and Equilibrium|page=765}}</ref>
:<math>{\Delta S^\circ}_{rxn} = S^\circ_{products} - S^\circ_{reactants}</math>

The standard entropy of reaction helps determine whether the reaction will take place [[spontaneous process|spontaneously]]. According to the [[second law of thermodynamics]], a spontaneous reaction always results in an increase in total entropy of the system and its surroundings:
:<math>(\Delta S_{total} = \Delta S_{system} + \Delta S_{surroundings})>0</math>
Molar entropy is not the same for all gases. Under identical conditions, it is greater for a heavier gas.