Standard molar entropy

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, dq_k/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]

• The heat capacity of one mole of the solid from 0 K to the crystal structures)
• The latent heat of fusion of the solid.
• The heat capacity of 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 Chemical equations make use of the standard molar entropy of reactants and products to find the standard entropy of reaction:

^[2]

ΔS°_rxn = S^o(products) - S^o (reactants)

The standard entropy of reaction helps determine whether the reaction will take place second law of thermodynamics, a spontaneous reaction always results in an increase in total entropy of the system and its surroundings:

ΔS_total = ΔS_system + ΔS_{surroundings > 0}

See also

• Entropy
• Heat
• Gibbs free energy
• Third law of thermodynamics

References