Standard Molar Entropy - Chemistry

Chemistry

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

• The heat capacity of one mole of the solid from 0 K to the melting point (including heat absorbed in any changes between different crystal structures)
• 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 products to find the standard entropy of reaction:

ΔS°_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:

ΔS_total = ΔS_system + ΔS_{surroundings > 0}