Standard Molar Entropy
Get Standard Molar Entropy essential facts below. View Videos or join the Standard Molar Entropy discussion. Add Standard Molar Entropy to your PopFlock.com topic list for future reference or share this resource on social media.
Standard Molar Entropy

In chemistry, the standard molar entropy is the entropy content of one mole of substance under a standard state (not STP).

The standard molar entropy is usually given the symbol S°, and has units of joules per mole kelvin (J mol-1 K-1). Unlike standard enthalpies of formation, the value of S° is absolute. That is, an element in its standard state has a definite, nonzero value of S at room temperature. The entropy of a pure crystalline structure can be 0 J mol-1 K-1 only at 0K, according to the third law of thermodynamics. However, this presupposes that the material forms a 'perfect crystal' without any frozen in entropy (defects, dislocations), which is never completely true because crystals always grow at a finite temperature. However this residual entropy is often quite negligible.

Thermodynamics

If a mole of substance were at 0 K, then warmed by its surroundings to 298 K, its total molar entropy would be the addition of all N individual contributions:

Here, dqk/T represents a very small exchange of heat energy at temperature T. The total molar entropy is the sum of many small changes in molar entropy, where each small change can be considered a reversible process.

Chemistry

The standard molar entropy of a gas at STP includes contributions from:[1]

Changes in entropy are associated with phase transitions and chemical reactions. Chemical equations make use of the standard molar entropy of reactants and products to find the standard entropy of reaction:[2]

?S°rxn = S°products - S°reactants

The standard entropy of reaction helps determine whether the reaction will take place 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:

?Stotal = ?Ssystem + ?Ssurroundings > 0

Molar entropy is not same for all gases. Under identical conditions, it is greater for heavier gas.

See also

References

  1. ^ Kosanke, K. (2004). "Chemical Thermodynamics". Pyrotechnic chemistry. Journal of Pyrotechnics. p. 29. ISBN 1-889526-15-0.
  2. ^ Chang, Raymond; Brandon Cruickshank (2005). "Entropy, Free Energy and Equilibrium". Chemistry. McGraw-Hill Higher Education. p. 765. ISBN 0-07-251264-4.

External links


  This article uses material from the Wikipedia page available here. It is released under the Creative Commons Attribution-Share-Alike License 3.0.

Standard_molar_entropy
 



 



 
Music Scenes